@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107304, title ="Petrogenesis of the post-collisional rare-metal-bearing Ad-Dayheen granite intrusion, Central Arabian Shield", author = "Abuamarah, Bassam A. and Azer, Mokhles K.", journal = "Lithos", month = "December", year = "2020", doi = "10.1016/j.lithos.2020.105956", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20210104-164231034", note = "© 2020 Published by Elsevier. \n\nReceived 31 October 2020, Revised 16 December 2020, Accepted 18 December 2020, Available online 27 December 2020. \n\nThe authors would like to extend their appreciation and gratitude to the King Saud University for funding and supporting this work through Researchers Supporting Project number (RSP-2020/151), King Saud University, Riyadh, Saudi Arabia. PDA is supported by the US NSF award EAR-1826310.\n\nDeclaration of interests:\nThe authors declare that they have no known competing financial interests or personal relationships\nthat could have appeared to influence the work reported in this paper.", revision_no = "12", abstract = "At Hadhb't Ad-Dayheen, in the central Arabian Shield, a post-collisional igneous complex called the Ad-Dayheen intrusion is exposed. It was emplaced in the Early Ediacaran (613–625\u202fMa), during the final tectono-magmatic stage of Arabian Shield development. Despite limited and discontinuous ring-shaped outcrops due to alluvial cover and later faulting, three pulses of intrusion can be recognized in the field: an early pulse of monzogranite; a second pulse of syenogranite and alkali feldspar granite; and a final pulse of alkaline and peralkaline granite, mineralized microgranite, and pegmatite. Samples show distinctively low contents of CaO, MgO, and Sr in contrast to elevated concentrations of alkalis, Rb, Nb, Y, Ta, Hf, Ga, Zr and rare-earth elements (REE); these are common characteristics of post-collisional rare-metal-bearing A-type granites. The suite displays positive Nbsingle bondTa anomalies and pronounced negative Eu anomalies (Eu/Eu*\u202f=\u202f0.11–0.35). The alkaline/peralkaline granites and microgranite of the Ad-Dayheen intrusion feature disseminated mineralization, whereas mineralization is localized in the pegmatite. The primary magma feeding the Ad-Dayheen intrusion was mostly generated by partial melting of the juvenile crust of the Arabian Shield, with a minor mantle contribution. We argue that an episode of lithospheric delamination led to crustal uplift, erosional decompression, and generation of mantle melts that supplied heat to drive crustal melting. The anatectic deep crustal melts assimilated a F-bearing component that also added rare metals to the magma. Each pulse can be described by a fractional crystallization model, but the parental liquid of each subsequent pulse was first modified by further addition of fluorine and rare metals and loss of CaO, Sr, Ba, and Eu due to fluorite fractionation. Texture and morphology of the ore minerals indicate that mineralization (U, Th, Zr, Nb, Ta, Y, Hf and REE) took place in two stages: a magmatic stage coinciding with emplacement of the intrusion, followed by a hydrothermal stage. The magmatic process enriched the residual melt in high field strength elements (HFSE) and REE. The later hydrothermal stage further localized these elements and increased their concentrations to economic grades. The pegmatite is highly mineralized and contains high concentrations of U (81–179\u202fμg/g), Th (244–600\u202fμg/g), Zr (2397–14,927\u202fμg/g), Nb (1352–2047\u202fμg/g), Ta (96–156\u202fμg/g), Y (828–2238\u202fμg/g), Hf (131–377\u202fμg/g) and ∑REE (1969–4761\u202fμg/g).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104924, title ="Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield", author = "Mubarak, Heba S. and Azer, Mokhles K.", journal = "Lithos", volume = "374-375", pages = "Art. No. 105720", month = "November", year = "2020", doi = "10.1016/j.lithos.2020.105720", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200812-083037133", note = "© 2020 Elsevier B.V. \n\nReceived 27 June 2020, Revised 28 July 2020, Accepted 28 July 2020, Available online 12 August 2020. \n\nWe acknowledge the National Research Centre (NRC), Egypt for logistical support of this work. The present manuscript is a part of the master's thesis of Heba S. Mubarak (the first author). PDA is supported by the US NSF, award 1947616. The authors are also indebted to the editor (Prof. Michael Roden) and two reviewers (Prof. Abdel-Aal M. Abdel-Karim and anonymous reviewer) for their efforts and numerous helpful comments. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "20", abstract = "We studied rodingite and rodingite-like rocks within a serpentinized ultramafic sequence and ophiolitic mélange at Um Rashid, in the Eastern Desert of Egypt. The Um Rashid ophiolite is strongly deformed, metamorphosed, and altered by serpentinization, carbonatization, listvenitization, rodingitization and silicification. The textures, whole-rock chemistry, and composition of fresh primary mineral relics show that the serpentinite protoliths were strongly melt-depleted harzburgite and minor dunite, typical of a supra-subduction zone fore-arc setting. The light-colored rocks replacing gabbro are divided on the basis of field relations, mineral assemblages and geochemical characteristics into typical rodingite and rodingite-like rock. Typical rodingite, found as blocks with chloritite blackwall rims within ophiolitic mélange, contains garnet, vesuvianite, diopside and chlorite with minor prehnite and opaque minerals. Rodingite-like rock, found as dykes in serpentinite, consists of hercynite, preiswerkite, margarite, corundum, prehnite, ferropargasite, albite, andesine, clinozoisite and diaspore. Some rodingite-like rock samples preserve relict gabbroic minerals and texture, whereas typical rodingite is fully replaced. Rodingite is highly enriched in CaO, Fe₂O₃, MgO, and compatible trace elements, whereas rodingite-like rock is strongly enriched in Al₂O₃ and incompatible trace elements. Based on geochemistry and petrographic evidence, both types of rodingitic rocks likely developed from mafic protoliths in immediate proximity to serpentinite but were affected by interaction with different fluids, most likely at different times. Typical rodingite development likely accompanied serpentinization and shows mineral assemblages characteristic of low-Si, high-Ca fluid infiltration at about 300 °C. Rodingite-like rock, on the other hand, likely developed from seawater infiltration.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106452, title ="Shock synthesis of Al-Fe-Cr-Cu-Ni icosahedral quasicrystal", author = "Hu, Jinping and Asimow, Paul D.", number = "2272", pages = "Art. No. 100013", month = "November", year = "2020", doi = "10.1063/12.0001005", isbn = "978-0-7354-4000-5", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201105-130517528", note = "© 2020 Author(s). Published by AIP Publishing. \n\nPublished Online: 04 November 2020. \n\nWe thank NASA Solar System Workings grant 80NSSC18K0532 for supporting this research. The Lindhurst Laboratory for Experimental Geophysics at Caltech is also supported by NSF awards EAR-1725349 and 1829277. We gratefully thank Jeff Nguyen from LLNL for providing the GDI. Constructive comments from the anonymous reviewer are appreciated.", revision_no = "9", abstract = "Al-alloy quasicrystals (QC) are of great interest because of their unique physical properties and natural occurrence in a meteorite. Considerable effort has been invested to explore the compositional fields of stable QC and quenchable metastable QC. In this light, shock recovery experiments, originally aimed at proving the planetary impact origin of natural quasicrystalline phases, also offer a novel strategy for synthesizing novel QC compositions and exploring expanded regions of the QC stability field. In this study, we shocked an Al-Cu-W graded density target (originally manufactured for use as a ramp-generating impactor but here used as target) to sample interactions between 304 stainless steel and the full range of Al/Cu starting ratios. This experiment synthesized an icosahedral quasicrystal of new composition Al₆₈Fe₂₀Cr₆Cu₄Ni₂. No previous reports of Al-Fe-Cr QCs have reached such high Fe/Cr ratio or low Al content. The Cr+Ni content is at the upper bound of this low-Cu quinary icosahedral QC according the Hume-Rothery rules for stability. Our synthesis suggests that the presence of Cu promotes the incorporation of Cr+Ni in the Al-rich icosahedral QC phase, enabling the high Fe/Cr ratio observed.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104355, title ="Petrogenesis of gold-bearing listvenites from the carbonatized mantle section of the Neoproterozoic Ess ophiolite, Western Arabian Shield, Saudi Arabia", author = "Gahlan, Hisham A. and Azer, Mokhles K.", journal = "Lithos", volume = "372-373", pages = "Art. No. 105679", month = "November", year = "2020", doi = "10.1016/j.lithos.2020.105679", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200713-122453085", note = "© 2020 Published by Elsevier B.V. \n\nReceived 12 June 2020, Revised 2 July 2020, Accepted 3 July 2020, Available online 12 July 2020. \n\nSpecial thanks are paid to King Saud University, Deanship of Scientific Research, Research Group No. RG-1436-036, for their support. PDA acknowledges support from the US NSF, award EAR-1947616. The authors are also indebted to the editor (Prof. Michael Roden) and two anonymous reviewers for their efforts and numerous helpful comments.\n\nDeclaration of Competing Interest:\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "22", abstract = "The variably serpentinized mantle peridotites of the Late Neoproterozoic Ess ophiolite (Western Saudi Arabia) are highly altered along shear zones and thrust planes to form erosion-resistant listvenites. The listvenites are distinguished petrographically and geochemically into three types: carbonate, silica-carbonate and silica (birbirite) listvenites. Geochemical analyses are consistent with expectations from petrography: carbonate listvenite is low in SiO₂ content but high in MgO, Fe₂O₃, and CaO relative to silica-carbonate and birbirite, which is remarkably high in SiO₂ at the expense of all other components. The total REE contents are low in silica-carbonate and carbonate listvenites but highly enriched in birbirite, with a large positive Eu anomaly. The host serpentinites have all the characteristics typically associated with highly depleted mantle harzburgite protoliths in supra-subduction fore-arc settings: bulk compositions are low in Al₂O₃ and CaO with high Mg# [molar Mg/(Mg + Fe)], relict Cr-spinel has high Cr# [molar Cr/(Cr + Al)] and low TiO₂, and relict olivine has high Mg# and NiO content. The Cr-spinel relics are also found in the listvenites; those in serpentinite and carbonate listvenites have significantly higher Mg# than those in silica-carbonate and birbirite, suggesting re-equilibration of Cr-spinel in the later phases of listvenitization. The varieties of listvenite capture successive stages of fluid-mediated replacement reactions. The carbonate listvenite appears to have developed syn-contemporaneously with serpentinization, whereas silica-carbonate listvenite and birbirite formed later. The listvenite formation resulted in leaching and removal of some components accompanied by deposition of others in the solid products, notably CO₃, SiO₂, REE (especially Eu), Au, Zn, As, Sb and K. Our data show that listvenitization concentrated gold at sub-economic to economic grades; measured gold concentrations in the host serpentinite are 0.5–1.7 ng/g, versus 4–2569 ng/g in carbonate listvenite, 43–3117 ng/g in silica-carbonate listvenite and 5–281 ng/g in birbirite. The listvenite deposits in the Jabal Ess area merit further exploration for gold.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105834, title ="The effects of solid-solid phase equilibria on the oxygen fugacity of the upper mantle", author = "Stolper, Edward M. and Shorttle, Oliver", journal = "American Mineralogist", volume = "105", number = "10", pages = "1445-1471", month = "October", year = "2020", doi = "10.2138/am-2020-7162", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201006-074914516", note = "© 2020 Mineralogical Society of America. \n\nManuscript received June 19, 2019; Manuscript accepted March 17, 2020; Manuscript handled by Maxim Ballmer. \n\nWe thank M.B. Baker, J.D. Blundy, E. Cottrell, J.M. Eiler, and B.J. Wood for helpful discussions and suggestions, and E. Cottrell, F. Davis, and B. Scaillet for helpful reviews. O.S. was supported at Caltech by a geology option postdoctoral fellowship and by a fellowship from Trinity College, Cambridge. P.D.A. and P.M.A. acknowledge support from NSF via award EAR-1550934. This manuscript was based on the first author’s 2017 Roebling Medal lecture.", revision_no = "10", abstract = "Decades of study have documented several orders of magnitude variation in the oxygen fugacity (fO₂) of terrestrial magmas and of mantle peridotites. This variability has commonly been attributed either to differences in the redox state of multivalent elements (e.g., Fe³⁺/Fe²⁺) in mantle sources or to processes acting on melts after segregation from their sources (e.g., crystallization or degassing). We show here that the phase equilibria of plagioclase, spinel, and garnet lherzolites of constant bulk composition (including whole-rock Fe³⁺/Fe²⁺) can also lead to systematic variations in fO₂ in the shallowest ~100 km of the mantle.\nTwo different thermodynamic models were used to calculate fO₂ vs. pressure and temperature for a representative, slightly depleted peridotite of constant composition (including total oxygen). Under subsolidus conditions, increasing pressure in the plagioclase-lherzolite facies from 1 bar up to the disappearance of plagioclase at the lower pressure limit of the spinel-lherzolite facies leads to an fO₂ decrease (normalized to a metastable plagioclase-free peridotite of the same composition at the same pressure and temperature) of ~1.25 orders of magnitude. The spinel-lherzolite facies defines a minimum in fO₂ and increasing pressure in this facies has little influence on fO₂ (normalized to a metastable spinel-free peridotite of the same composition at the same pressure and temperature) up to the appearance of garnet in the stable assemblage. Increasing pressure across the garnet-lherzolite facies leads to increases in fO₂ (normalized to a metastable garnet-free peridotite of the same composition at the same pressure and temperature) of ~1 order of magnitude from the low values of the spinel-lherzolite facies. These changes in normalized fO₂ reflect primarily the indirect effects of reactions involving aluminous phases in the peridotite that either produce or consume pyroxene with increasing pressure: Reactions that produce pyroxene with increasing pressure (e.g., forsterite + anorthite ⇄ Mg-Tschermak + diopside in plagioclase lherzolite) lead to dilution of Fe³⁺-bearing components in pyroxene and therefore to decreases in normalized fO₂, whereas pyroxene-consuming reactions (e.g., in the garnet stability field) lead initially to enrichment of Fe³⁺-bearing components in pyroxene and to increases in normalized fO₂ (although this is counteracted to some degree by progressive partitioning of Fe³⁺ from the pyroxene into the garnet with increasing pressure). Thus, the variations in normalized fO₂ inferred from thermodynamic modeling of upper mantle peridotite of constant composition are primarily passive consequences of the same phase changes that produce the transitions from plagioclase → spinel → garnet lherzolite and the variations in Al content in pyroxenes within each of these facies. Because these variations are largely driven by phase changes among Al-rich phases, they are predicted to diminish with the decrease in bulk Al content that results from melt extraction from peridotite, and this is consistent with our calculations.\nObserved variations in FMQ-normalized fO₂ of primitive mantle-derived basalts and peridotites within and across different tectonic environments probably mostly reflect variations in the chemical compositions (e.g., Fe³⁺/Fe²⁺ or bulk O₂ content) of their sources (e.g., produced by subduction of oxidizing fluids, sediments, and altered oceanic crust or of reducing organic material; by equilibration with graphite- or diamond-saturated fluids; or by the effects of partial melting). However, we conclude that in nature the predicted effects of pressure- and temperature-dependent phase equilibria on the fO₂ of peridotites of constant composition are likely to be superimposed on variations in fO₂ that reflect differences in the whole-rock Fe³⁺/Fe²⁺ ratios of peridotites and therefore that the effects of phase equilibria should also be considered in efforts to understand observed variations in the oxygen fugacities of magmas and their mantle sources.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105780, title ="Petrogenetic Evolution of the Neoproterozoic Igneous Rocks of Egypt", author = "Azer, Mokhles K. and Asimow, Paul D.", pages = "343-382", month = "September", year = "2020", doi = "10.1007/978-3-030-49771-2_13", issn = "2364-6438", isbn = "978-3-030-49770-5", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201005-095755660", note = "© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021. \n\nFirst Online: 30 September 2020. \n\nThe authors would like to thank the Main Editor Zakaria Hamimi for expert handling of the manuscript, as well as reviewers Jean-Paul Liégeois, Arild Andresen, and an anonymous reviewer. PDA’s work on the petrology of Egypt is supported by the US National Science Foundation, award 1947616.", revision_no = "7", abstract = "The Late Neoproterozoic basement exposures in the Sinai Peninsula and Eastern Desert of Egypt represent the northern part of the Nubian Shield, which was contiguous with the Arabian shield before the opening of the Red Sea. These two Shields together form the Arabian-Nubian Shield (ANS). The ANS, formed during the Neoproterozoic Pan-African orogeny due to collision between East and West Gondwana, is the best-preserved juvenile continental crust of Neoproterozoic age on Earth. The Nubian shield evolved through a series of stages that can be characterized as (1) supercontinent rift and drift (1000–900 Ma), (2) subduction and consumption of intervening ocean basins (870–750 Ma), (3) continental collision and orogeny (750–630 Ma), and (4) post-orogenic extension and collapse (620–580 Ma plus minor later activity extending to 540 Ma). The Neoproterozoic (870–580 Ma) development of the juvenile continental crust specifically of the Egyptian Nubian Shield segment of the ANS, however, is most logically discussed in three main stages: pre-collisional, collisional, and post-collisional. The pre-collisional phase (~870–700 Ma) produced complete oceanic ophiolite assemblages coexisting with intra-oceanic island arcs. All the Egyptian Eastern Desert ophiolites are strongly deformed, metamorphosed, and affected by several types of alteration. They occur as dismembered, tectonized bodies and mélanges of pillowed metabasalt, gabbro, and variably altered ultramafic rocks. Along shear zones, the ophiolitic ultramafics are highly altered into talc-carbonates, magnesite, and listvenite. The collisional stage (670–630 Ma) includes a subduction period that produced volcano-sedimentary island arc successions and calc-alkaline gabbro–diorite complexes, followed by development of Cordilleran-style calc-alkaline gabbros and granodiorites and their extrusive equivalents, ending with the merger of West and East Gondwana. All the units of the collisional stage are weakly deformed and experienced only low-grade metamorphism. The post-collisional phase (~620–580 Ma) was characterized by intracrustal melting that first generated calc-alkaline granitoids and then gradually shifted to a terminal stage that produced relatively small volumes of alkaline magma, preserved as both plutonic and volcanic units. Temporally, the later stages of post-collisional calc-alkaline magmatism and the alkaline magmatism overlapped. This chapter discusses the evolution of the Nubian from an igneous petrology perspective, including the plutonic (granitoid and mafic–ultramafic) and volcanic records. Granitoids were emplaced in Egypt during each phase of evolution of the Nubian Shield: pre-collisional granitoids include highly deformed trondhjemite, tonalite, and granodiorite; syn-collisional granitoids are weakly deformed granodiorite and less commonly granite; post-collisional granitoids include undeformed calc-alkaline and alkaline monzogranite, syenogranite, alkali feldspar granite, and alkaline/peralkaline granites. The Neoproterozoic mafic–ultramafic complexes in the Egyptian Nubian Shield include older and younger complexes. The older mafic–ultramafic complexes either form an integral part of obducted ophiolite sequences or constitute members of subduction-related, calc-alkaline gabbro–diorite complexes. The younger mafic–ultramafic complexes are mostly fresh, undeformed, and unmetamorphosed, and were emplaced in post-orogenic settings. Four major volcanic episodes have been recognized in the Neoproterozoic crust of Egypt, including ophiolitic metavolcanic rocks, island arc metavolcanic rocks, the Dokhan volcanic series, and post-collisional alkaline volcanics (Katherina Volcanics).", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105805, title ="The Mantle Section of Neoproterozoic Ophiolites from the Pan-African Belt, Eastern Desert, Egypt: Tectonomagmatic Evolution, Metamorphism, and Mineralization", author = "Gahlan, Hisham A. and Azer, Mokhles K.", pages = "309-341", month = "September", year = "2020", doi = "10.1007/978-3-030-49771-2_12", issn = "2364-6438", isbn = "978-3-030-49770-5", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201005-130234882", note = "© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021. \n\nFirst Online: 30 September 2020. \n\nHisham A. Gahlan owes the debt of gratitude to Assiut University, as well as King Saud University, Deanship of Scientific Research for their support.", revision_no = "7", abstract = "The Eastern Desert (ED) Neoproterozoic ophiolites are tectonically important elements of the Arabian–Nubian Shield. Although affected by various degrees of dismemberment, metamorphism, and alteration, almost all of the diagnostic Penrose-type ophiolite components can be found, namely, lower units of serpentinized peridotite tectonite and cumulate ultramafics and upper units of layered and isotropic gabbros, plagiogranites, sheeted dykes and pillow lavas. The contacts between the lower unit (mantle section) and the upper unit (crustal section) were originally magmatic, but in all cases are now disrupted by tectonism. The mantle sections of the ED ophiolites are exposed as folded thrust sheets bearing important and distinctive lithologies of serpentinized peridotites of harzburgite and dunite protoliths with occasional podiform chromitites. The ED ophiolites show a spatial and temporal association with suture zones that indicate fossil subduction zone locations. Multiple episodes of regional metamorphism mostly reached greenschist facies with less common amphibolite facies localities. CO₂-metasomatism resulted in the development of talc–carbonate, listvenite, magnesite, and other carbonate-bearing meta-ultramafic rocks. Geochemical data from the ED serpentinites, despite some confounding effects of hydration and alteration, resemble modern oceanic peridotites. The ED serpentinites show high LOI (≤20 wt%); Mg# mostly higher than 0.89; enrichment of Ni, Cr, and Co; depletion of Al₂O₃ and CaO; and nearly flat, depleted, and unfractionated chondrite-normalized REE patterns. The modal abundance of clinopyroxene is very low if it is present at all. Chromian spinel survived metamorphism and is widely used as the most reliable petrogenetic and geotectonic indicator in the ED ophiolite mantle sections. The high-Cr# (mostly\u2009~0.7) and low-TiO₂ (mostly\u2009≤\u20090.1 wt%) characters of chromian spinel indicate a high degree of partial melt extraction (≥30%), which is commonly associated with fore-arc settings and equilibration with boninite-like or high-Mg tholeiite melts. Based on the general petrological characteristics, the ED ophiolitic chromitites are largely similar to Phanerozoic examples that have been attributed to melt–peridotite interaction and subsequent melt mixing in fore-arc settings. The comparison between the ED Neoproterozoic mantle peridotites and Phanerozoic equivalents indicates considerable similarity in tectonomagmatic processes and does not support any major changes in the geothermal regime of subduction zones on Earth since the Neoproterozoic era. The mantle sections of ED ophiolites are worthy targets for mining and exploration, hosting a variety of ores (chromite, gold, and iron/nickel laterites) and industrial minerals (talc, asbestos, and serpentine).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105096, title ="Configurational entropy of basaltic melts in Earth’s mantle", author = "Lee, Sung Keun and Mosenfelder, Jed L.", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "117", number = "36", pages = "21938-21944", month = "September", year = "2020", doi = "10.1073/pnas.2014519117", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200825-084943976", note = "© 2020 National Academy of Sciences. Published under the PNAS license. \n\nEdited by W. G. Ernst, Stanford University, Stanford, CA, and approved August 5, 2020 (received for review July 10, 2020). PNAS first published August 24, 2020. \n\nThis study was supported by a grant from the National Research Foundation, Korea (2017R1A2A1A17069511 and 2020R1A3B2079815), to S.K.L. We appreciate reviewers’ constructive comments, which greatly improved the quality and clarity of the manuscript. \n\nData Availability: All study data are included in the article and SI Appendix. \n\nAuthor contributions: S.K.L. designed research; S.K.L., J.L.M., and S.Y.P. performed research; S.K.L., J.L.M., S.Y.P., and P.D.A. contributed new reagents/analytic tools; S.K.L., S.Y.P., and A.C.L. analyzed data; and S.K.L., J.L.M., and P.D.A. wrote the paper. \n\nThe authors declare no competing interest. \n\nThis article is a PNAS Direct Submission. \n\nThis article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2014519117/-/DCSupplemental.", revision_no = "20", abstract = "Although geophysical observations of mantle regions that suggest the presence of partial melt have often been interpreted in light of the properties of basaltic liquids erupted at the surface, the seismic and rheological consequences of partial melting in the upper mantle depend instead on the properties of interstitial basaltic melt at elevated pressure. In particular, basaltic melts and glasses display anomalous mechanical softening upon compression up to several GPa, suggesting that the relevant properties of melt are strongly pressure-dependent. A full understanding of such a softening requires study, under compression, of the atomic structure of primitive small-degree basaltic melts at their formation depth, which has proven to be difficult. Here we report multiNMR spectra for a simplified basaltic glass quenched at pressures up to 5 GPa (corresponding to depths down to ∼150 km). These data allow quantification of short-range structural parameters such as the populations of coordination numbers of Al and Si cations and the cation pairs bonded to oxygen atoms. In the model basaltic glass, the fraction of ^([5,6])Al is ∼40% at 5 GPa and decreases to ∼3% at 1 atm. The estimated fraction of nonbridging oxygens at 5 GPa is ∼84% of that at ambient pressure. Together with data on variable glass compositions at 1 atm, these results allow us to quantify how such structural changes increase the configurational entropy of melts with increasing density. We explore how configurational entropy can be used to explain the anomalous mechanical softening of basaltic melts and glasses.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103162, title ="Atud Gabbro-Diorite Complex: Glimpse of the Cryogenian Mixing, Assimilation, Storage, and Homogenization Zone beneath the Eastern Desert of Egypt", author = "Stern, Robert J. and Ali, Kamal", journal = "Journal of the Geological Society", volume = "117", number = "5", pages = "965-980", month = "September", year = "2020", doi = "10.1144/jgs2019-199", issn = "0016-7649", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200513-071910901", note = "© 2020 The Author(s). Published by The Geological Society of London. \n\nReceived 2 December 2019; Revised 28 April 2020; Accepted 30 April 2020. \n\nWe appreciate thoughtful and constructive reviews by J.-P. Liégeois and R. A. Terentiev. K. Lindén and H. Jeon are thanked for assistance with the SIMS analyses. The Nordsim laboratory operates as a Swedish Research Council infrastructure under grant 2017-00671; this is Nordsim contribution 639. This is UTD Geosciences contribution number 1353. \n\nThis work was funded by the Directorate for Geosciences (OCE-1826310). \n\nAuthor contributions: RS: conceptualization (lead), formal analysis (lead), visualization (lead), writing – original draft (lead), writing – review & editing (lead); KA: investigation (supporting), visualization (supporting), writing – review & editing (supporting); PA: formal analysis (supporting), writing – original draft (supporting); MA: investigation (supporting), writing – original draft (supporting), writing – review & editing (supporting); MIL: investigation (supporting), visualization (supporting), writing – original draft (supporting), writing – review & editing (supporting); HSM: investigation (supporting), writing – original draft (supporting); MR: investigation (supporting), visualization (supporting), writing – original draft (supporting); RLR: investigation (equal), visualization (equal), writing – review & editing (equal); MW: investigation (equal), visualization (equal), writing – review & editing (equal). \n\nData availability statement: All data generated or analysed during this study are included in this published article (and its supplementary information files).", revision_no = "21", abstract = "We analysed gabbroic and dioritic rocks from the Atud igneous complex in the Eastern Desert of Egypt to understand better the formation of juvenile continental crust of the Arabian–Nubian Shield. Our results show that the rocks are the same age (U–Pb zircon ages of 694.5\u2009±\u20092.1 Ma for two diorites and 695.3\u2009±\u20093.4 Ma for one gabbronorite). These are partial melts of the mantle and related fractionates (εNd₆₉₀\u2009=\u2009+4.2 to +7.3, ⁸⁷Sr/⁸⁶Sr_i\u2009=\u20090.70246–0.70268, zircon δ¹⁸O ∼ +5‰). Trace element patterns indicate that Atud magmas formed above a subduction zone as part of a large and long-lived (c. 60 myr) convergent margin. Atud complex igneous rocks belong to a larger metagabbro–epidiorite–diorite complex that formed as a deep crustal mush into which new pulses of mafic magma were periodically emplaced, incorporated and evolved. The petrological evolution can be explained by fractional crystallization of mafic magma plus variable plagioclase accumulation in a mid- to lower crustal MASH zone. The Atud igneous complex shows that mantle partial melting and fractional crystallization and plagioclase accumulation were important for Cryogenian crust formation in this part of the Arabian–Nubian Shield.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102699, title ="Assessment of magmatic versus post-magmatic processes in the Mueilha rare-metal granite, Eastern Desert of Egypt, Arabian-Nubian Shield", author = "Seddik, Amany M. A. and Darwish, Mahmoud H.", journal = "Lithos", volume = "366-367", pages = "Art. No. 105542", month = "August", year = "2020", doi = "10.1016/j.lithos.2020.105542", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200421-125254344", note = "© 2020 Elsevier B.V. \n\nReceived 2 March 2020, Revised 15 April 2020, Accepted 15 April 2020, Available online 21 April 2020. \n\nWe acknowledge the National Research Centre, Egypt for supporting this study as a part of the internal project (No. 12010306) of studies of the rare-metal bearing granites in the Eastern Desert of Egypt. This work is a part of the master's thesis of Amany M.A. Seddik (the first author). PDA is support by the US NSF through award 1550934. The authors highly appreciate thoughtful reviews by the two anonymous reviewers. In addition, the authors are also indebted to the editor (Prof. Michael Roden) for his efforts and numerous helpful comments. \n\nThe authors declare no competing financial interests or personal relationships that could have influenced the work presented herein.", revision_no = "30", abstract = "The Mueilha rare-metal granite, exposed in the central Eastern Desert of Egypt, is a post-collisional intrusion that formed in the final magmatic stage of the evolution of the Arabian-Nubian Shield. The Mueilha intrusion was emplaced as a high-level magmatic cupola into metamorphic country rocks. It consists of two cogenetic intrusive bodies: an early phase emplaced at shallow depth and now penetratively altered to white albite granite and a later phase of red granites emplaced at greater depth that better preserve magmatic features. The albite granite is less common and represents the upper margin of the Mueilha intrusion, the apex of the magmatic cupola. The red granites are volumetrically dominant and appears to have crystallized from the margins inward, forming a composite pluton zoned from muscovite granite to alkali feldspar granite. All parts of the Mueilha pluton appear to have been emplaced within a short time interval, before complete crystallization of the earliest phase. The geochemistry of the Mueilha granites is typical of rare-metal granites, characterized by high SiO₂, Na₂O + K₂O, Nb, Rb, Ta, Y, U, Th, Sn, and W with depletion in P, Mg, Ti, Sr and Ba. They are weakly peraluminous and highly fractionated with A-type character. The chondrite-normalized REE patterns have strongly negative Eu anomalies, typical of highly differentiated granites that evolved through a transitional magmatic–hydrothermal stage. The primary magma feeding the Mueilha intrusion was generated by partial melting of the juvenile crust of the Arabian-Nubian Shield; it subsequently underwent extensive fractional crystallization and metasomatism by late- to post-magmatic fluids. Separation of fluids from the oversaturated melt promoted both diffuse greisenization and focused segregation of pegmatite and fluorite and quartz veins. Alkalis liberated from feldspars consumed by greisenization were redeposited during albitization in the uppermost part of the magma chamber. Despite penetration of the intrusion boundary by discrete dikes, veins, and aphophyses, diffuse alteration of the metamorphic country rocks is not apparent. Primary columbite-series minerals crystallized from the melt and were later partly replaced by secondary Nb and Ta minerals (fluorcalciomicrolite and wodginite) during hydrothermal alteration.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104769, title ="Toward an international practical pressure scale: A proposal for an IPPS ruby gauge (IPPS-Ruby2020)", author = "Shen, Guoyin and Wang, Yanbin", journal = "High Pressure Research", volume = "40", number = "3", pages = "299-314", month = "July", year = "2020", doi = "10.1080/08957959.2020.1791107", issn = "0895-7959", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200806-065909934", note = "© 2020 Taylor and Francis. \n\nReceived 27 Jun 2020, Accepted 30 Jun 2020, Published online: 23 Jul 2020. \n\nWe thank the AIRAPT Executive Committee for the support of the IPPS task force activities. We thank Dr. Karl Syassen for his contribution to the establishment of Ruby2020. We also thank Drs. Steven Jacobsen and Thomas Duffy for useful discussions. GS acknowledges the support of HPCAT operations by Department of Energy (DOE)-NNSA's Office of Experimental Sciences. YW acknowledges the support of GeoSoilEnviroCARS, which is supported by the National Science Foundation – Earth Sciences (EAR – 1634415) and DOE-GeoSciences (DE-FG02-94ER14466). \n\nThis work was supported by National Science Foundation: [Grant Number EAR –1634415]; Department of Energy - Department of Energy (DOE)-NNSA’s Office of Experimental Sciences; Department of Energy, Geosciences: [Grant Number DE-FG02-94ER14466]. \n\nNo potential conflict of interest was reported by the author(s).", revision_no = "16", abstract = "At the 26th AIRAPT conference in 2017, a task group was formed to work on an International Practical Pressure Scale (IPPS). This report summarizes the activities of the task group toward an IPPS ruby gauge. We have selected three different approaches to establishing the relation between pressure (P) and ruby R1-line shift (Δλ) with three groups of optimal reference materials for applying these approaches. Using a polynomial form of the second order, the recommended ruby gauge (referred as Ruby2020) is expressed by: P[GPa] = 1.87(±0.01) × 10³ (Δλ/λ₀)[1+5.63(±0.03)(Δλ/λ₀)], where λ₀ is the wavelength of the R1-line near 694.25 nm at ambient condition. In June of 2020, the Executive Committee of AIRAPT endorsed the proposed Ruby2020. We encourage high-pressure practitioners to utilize Ruby2020 within its applicable pressure range (up to 150 GPa), so that pressure data can be directly compared across laboratories and amended consistently as better scales emerge in the future.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102464, title ="Identifying high potential zones of gold mineralization in a sub-tropical region using Landsat-8 and ASTER remote sensing data: a case study of the Ngoura-Colomines goldfield, Eastern Cameroon", author = "Wambo, Jonas Didero Takodjou and Pour, Amin Beiranvand", journal = "Ore Geology Reviews", volume = "122", pages = "Art. No. 103530", month = "July", year = "2020", doi = "10.1016/j.oregeorev.2020.103530", issn = "0169-1368", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200409-142455588", note = "© 2020 Elsevier B.V. \n\nReceived 19 February 2019, Revised 14 February 2020, Accepted 7 April 2020, Available online 8 April 2020.", revision_no = "9", abstract = "Climatic conditions and vegetation constrain the use of optical satellite imagery as an exploration tool for hydrothermal ore mineralization in tropical and subtropical regions. In this investigation, Landsat-8 and ASTER satellite imagery were used to detect hydrothermal alteration zones associated with gold mineralization in the Ngoura-Colomines region, Eastern Cameroon. The study area contains several gold-bearing quartz veins associated with zones of pyritization, muscovite/sericite, iron oxides, and silicification. Principal Component Analysis (PCA), Independent Component Analysis (ICA), and specialized spectral band ratios were used to extract spectral information related to vegetation, iron oxide/hydroxide minerals, Al–OH, Fe-Mg–OH, carbonate group minerals, and silicification using Landsat-8 data at regional scale. Linear Spectral Unmixing (LSU) algorithm was implemented to ASTER VNIR+SWIR bands for detailed discrimination of hematite, jarosite, kaolinite, muscovite, chlorite and epidote at district scale. The Automated Spectral Hourglass (ASH) technique was employed to extract reference spectra directly from the ASTER bands for producing fraction images of end-members using the LSU. A comprehensive field survey was used to verify the remote sensing results. Petrographic study, X-ray diffraction analysis and reflectance spectroscopy indicated the presence of quartz, goethite and sericite, as well as the absorption features of Fe³⁺/Fe²⁺, Al–OH, OH/H2O and SiO₂ in the alteration zones. Several hydrothermal alteration zones of iron oxide/hydroxide, clay, carbonate minerals and silicification zones were identified, which are spatially associated with known mining areas and gold occurrences in the study area. High potential prospects were also delineated, including the Ngoura-Colomines prospects and the newly discovered Yangamo-Ndatanga and Taparé-Tapondo prospects in the southwestern and southeastern parts of the study area. Consequently, satellite-based mineral prospectivity maps at regional and district scales were generated for the study area by implementing the fuzzy logic model to the most informative thematic layers derived from image processing results. The satellite-based prospectivity maps are reliable for exploration of new gold prospective zones in the Ngoura-Colomines goldfield.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102355, title ="Water-in-olivine magma ascent chronometry: Every crystal is a clock", author = "Newcombe, Megan E. and Plank, Terry", journal = "Journal of Volcanology and Geothermal Research", volume = "398", pages = "Art. No. 106872", month = "June", year = "2020", doi = "10.1016/j.jvolgeores.2020.106872", issn = "0377-0273", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200406-131646410", note = "© 2020 Published by Elsevier B.V. \n\nReceived 18 September 2019, Revised 25 March 2020, Accepted 31 March 2020, Available online 4 April 2020.", revision_no = "13", abstract = "The syneruptive decompression rate of basaltic magma in volcanic conduits is thought to be a critical control on eruptive vigor. Recent efforts have constrained decompression rates using models of diffusive water loss from melt embayments, olivine-hosted melt inclusions and clinopyroxene phenocrysts; however, these techniques are difficult to apply because of the rarity of pyroxene crystals or melt embayments suitable for analysis and the complexities associated with modeling water loss from melt inclusions. We have developed a new magma ascent chronometer based on syneruptive diffusive water loss from olivine phenocrysts. \n\nWe have found water zonation in every olivine phenocryst we have measured, from explosive eruptions of Seguam, Fuego, Kilauea and Cerro Negro volcanoes. The majority of the olivine phenocrysts were polished to expose a central plane normal to the crystallographic ‘b’ axis and volatile concentration profiles were measured along ‘a’ and ‘c’ axes by secondary ion mass spectrometry (SIMS). Profiles are compared to 1D and 3D finite-element models of diffusive water loss from olivine, whose boundaries are in equilibrium with a melt undergoing closed-system degassing.\n\nLeast-squares fitting of measured water concentration gradients in olivine to a 1D Monte Carlo model produces constraints on magma decompression rates that are in good agreement with independent constraints from melt embayment studies and modeling of water loss from olivine-hosted melt inclusions at Fuego, Seguam, Kilauea, and Cerro Negro. Such agreement confirms the accuracy and sensitivity of the water-in-olivine chronometer over a range of decompression rates (dP/dt) spanning ~2 orders of magnitude (from 0.007 to 0.45 MPa/s). We find that the assumption of a zero-water boundary condition (in which the water concentration at the edges of the olivine phenocrysts is fixed at 0 ppm throughout their ascent) leads to an overestimation of the decompression rate by an order of magnitude compared to the closed-system degassing boundary condition assumed in our model, thereby highlighting the sensitivity of the water-in-olivine chronometer to the host magma degassing path.\n\nAt Seguam, a wide range of best-fit values of dP/dt is obtained both from the water-in-olivine chronometer (0.04–0.23 MPa/s) and from melt embayments (0.02–0.13 MPa/s). We find systematically higher dP/dt values in the melt embayments that appear to have stalled or crystallized at the shallowest depths. Together, these observations are suggestive of magma acceleration during ascent.\n\nA strength of the water-in-olivine chronometer is the prevalence of olivine in mafic to intermediate magmas. This new technique yields many values of dP/dt from a single eruption, providing insight into the diversity of ascent records carried by the crystal cargo and possibly defining changes in dP/dt through time and space. This data density offers a more detailed window into syneruptive conduit processes than has been possible using other techniques for constraining dP/dt. In theory, each crystal is a clock, with the potential to record variable ascent in the conduit, over the course of an eruption, between eruptions, and among volcanic systems.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102019, title ="Shoshonitic enclaves in the high Sr/Y Nyemo pluton, southern Tibet: Implications for Oligocene magma mixing and the onset of extension of the southern Lhasa terrane", author = "Wang, Zhenzhen and Zhao, Zhidan", journal = "Lithos", volume = "362-363", pages = "Art. No. 105490", month = "June", year = "2020", doi = "10.1016/j.lithos.2020.105490", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200320-085750658", note = "© 2020 Published by Elsevier B.V. \n\nReceived 4 December 2019, Revised 17 March 2020, Accepted 18 March 2020, Available online 20 March 2020. \n\nWe thank editor Xian-Hua Li for handling this manuscript and two anonymous reviewers for constructive comments. We are grateful to Liyuan Xing and Yan Tang for assistance of fieldwork in Tibet and geochemical analyses. This research was supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (grant 2019QZKK0702), the National Key Research and Development Project of China (project 2016YFC0600304), the Natural Science Foundation of China (grant 41802058), the Fundamental Research Funds for the Central Universities (grants 2652018122 and QZ05201902), and the 111 Project of the Ministry of Science and Technology of China (projects BP0719021 and B18048). ZW acknowledges a fellowship from the China Scholarship Council (CSC No. 201806400019). \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "24", abstract = "Post-collisional potassic and high Sr/Y magmatism in the Lhasa terrane provides critical constraints on the timing and mechanism of subduction of Indian lithosphere and its role in the uplift of the Tibetan Plateau. Here, we report whole-rock geochemistry, mineral geochemistry, zircon U Pb ages, and in situ zircon Hf isotope ratios for the Nyemo pluton, a representative example of such magmatism. The Nyemo pluton is composed of high Sr/Y host rocks and coeval shoshonitic mafic microgranular enclaves (MMEs). Whole-rock compositions of the host rocks and MMEs form linear trends in Harker diagrams, consistent with modification of both end-members by magma mixing. Although the main high Sr/Y phase of the pluton formed by partial melting of the lower crust of the thickened Lhasa terrane, the MMEs display abnormally enriched light rare earth elements, low whole-rock ε_(Nd)(t) and low zircon ε_(Hf)(t) that suggest derivation from low degree melting of hydrous and enriched mantle. Based on the occurrence of shoshonitic magma and high La/Yb and high Sr/Y with adakitic affinity host rocks around 30 Ma, the Nyemo pluton is best explained as a record of onset of extension that resulted from convective removal of the mantle lithosphere beneath Tibet in the Oligocene.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100198, title ="Tracking the transition from subduction‐related to post‐collisional magmatism in the north Arabian–Nubian Shield: A case study from the Homrit Waggat area of the Eastern Desert of Egypt", author = "Azer, Mokhles K. and Abdelfadil, Khaled M.", journal = "Geological Journal", volume = "55", number = "6", pages = "4426-4452", month = "June", year = "2020", doi = "10.1002/gj.3643", issn = "0072-1050", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191205-091824321", note = "© 2019 John Wiley & Sons, Ltd. \n\nVersion of Record online: 18 November 2019; Manuscript accepted: 08 August 2019; Manuscript revised: 23 May 2019; Manuscript received: 27 December 2017. \n\nFunding Information: U.S. National Science Foundation. Grant Number: EAR‐1550934.", revision_no = "14", abstract = "Field and geochemical observations of the granitoids of the Homrit Waggat area in the central Eastern Desert of Egypt reveal two magmatic phases. The early phase of weakly deformed subduction‐related calc‐alkaline rocks includes tonalite and granodiorite. We name the later phase the Homrit Waggat Pluton (HWP); it includes undeformed syenogranite, alkali feldspar granite, and minor albitized granite. The tonalite and granodiorite have distinct negative Nb–Ta anomalies and lower alkalis, REE, Nb, Zr, and Hf than the HWP. The early magmatic pulse is a subduction‐related suite, likely generated by underplating of mantle‐derived magmas that triggered partial melting of mafic lower crust; mixing of these melts led to intermediate magma that further fractionated to tonalite and granodiorite. The HWP granites of the late magmatic pulse are transitional from a subduction‐related to an anorogenic within‐plate environment, plausibly generated by post‐collisional lithosphere delamination. Although the parent magma of the HWP was I‐type, extensive fractional crystallization produced residual liquids with A₂‐type character. Albitized granites are found only along the outer margin of the HWP, and contacts with the alkali feldspar granite are gradational, suggesting fluid interactions at a late stage of crystallization. The original textures of the albitized granites are preserved, but their bulk composition was modified by the production of Na‐rich minerals and the removal of K, REE, and some trace elements by fluids.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103098, title ="First synthesis of a unique icosahedral phase from the Khatyrka meteorite by shock-recovery experiment", author = "Hu, Jinping and Asimow, Paul D.", journal = "International Union of Crystallography Journal", volume = "7", number = "3", pages = "434-444", month = "May", year = "2020", doi = "10.1107/s2052252520002729", issn = "2052-2525", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200511-101653760", note = "© 2020 International Union of Crystallography. This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited. \n\nReceived 19 December 2019; Accepted 26 February 2020. \n\nWe are grateful to Jeffrey Nguyen from Lawrence Livermore National Lab for providing the GDI. We thank Matthias Ebert and two anonymous reviewers for their constructive comments. \n\nWe thank NASA Solar System Workings grant 80NSSC18K0532 for supporting JH and this research. The Lindhurst Laboratory for Experimental Geophysics at Caltech is also supported by NSF awards EAR-1725349 and 1829277. LB is funded by MIUR-PRIN2017, project 'TEOREM - deciphering geological processes using terrestrial and extraterrestrial ORE minerals', prot. 2017AK8C32 (PI: Luca Bindi). Analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065.", revision_no = "17", abstract = "Icosahedral quasicrystals (i-phases) in the Al–Cu–Fe system are of great interest because of their perfect quasicrystalline structure and natural occurrences in the Khatyrka meteorite. The natural quasicrystal of composition Al₆₂Cu₃₁Fe₇, referred to as i-phase II, is unique because it deviates significantly from the stability field of i-phase and has not been synthesized in a laboratory setting to date. Synthetic i-phases formed in shock-recovery experiments present a novel strategy for exploring the stability of new quasicrystal compositions and prove the impact origin of natural quasicrystals. In this study, an Al–Cu–W graded density impactor (GDI, originally manufactured as a ramp-generating impactor but here used as a target) disk was shocked to sample a full range of Al/Cu starting ratios in an Fe-bearing 304 stainless-steel target chamber. In a strongly deformed region of the recovered sample, reactions between the GDI and the steel produced an assemblage of co-existing Al_(61.5)Cu_(30.3)Fe_(6.8)Cr_(1.4) i-phase II + stolperite (β, AlCu) + khatyrkite (θ, Al₂Cu), an exact match to the natural i-phase II assemblage in the meteorite. In a second experiment, the continuous interface between the GDI and steel formed another more Fe-rich quinary i-phase (Al_(68.6)Fe_(14.5)Cu_(11.2)Cr₄Ni_(1.8)), together with stolperite and hollisterite (λ, Al₁₃Fe₄), which is the expected assemblage at phase equilibrium. This study is the first laboratory reproduction of i-phase II with its natural assemblage. It suggests that the field of thermodynamically stable icosahedrite (Al₆₃Cu₂₄Fe₁₃) could separate into two disconnected fields under shock pressure above 20 GPa, leading to the co-existence of Fe-rich and Fe-poor i-phases like the case in Khatyrka. In light of this, shock-recovery experiments do indeed offer an efficient method of constraining the impact conditions recorded by quasicrystal-bearing meteorite, and exploring formation conditions and mechanisms leading to quasicrystals.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/101416, title ="Suprasubduction-zone origin of the podiform chromitites of the Bir Tuluhah ophiolite, Saudi Arabia, during Neoproterozoic assembly of the Arabian Shield", author = "Abuamarah, Bassam A. and Asimow, Paul D.", journal = "Lithos", volume = "360-361", pages = "Art. No. 105439", month = "May", year = "2020", doi = "10.1016/j.lithos.2020.105439", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200220-092957322", note = "© 2020 Published by Elsevier B.V. \n\nReceived 10 January 2020, Revised 16 February 2020, Accepted 17 February 2020, Available online 20 February 2020. \n\nThe authors would like to extend their appreciation and gratitude to the King Saud University for funding and supporting this work through Researchers Supporting Project number (RSP-2019/151), King Saud University, Riyadh, Saudi Arabia. PDA is supported by the US NSF award EAR-1826310. In addition, the authors highly appreciate thoughtful reviews by Prof. Hilmy E. Moussa and an anonymous reviewer. The authors are also indebted to the editor (Prof. Michael Roden) for his efforts and numerous helpful comments. \n\nDeclaration of Competing Interest: None.", revision_no = "25", abstract = "The ultramafic section of a dismembered ophiolite is exposed at Bir Tuluhah, in the north-central part of the Arabian Shield. It is penetratively serpentinized and locally carbonate-altered to talc‑carbonate and quartz‑carbonate rocks (listvenite) along shear zones and fault planes. Despite the high degree of mineral replacement, preserved mesh and bastite textures and fresh relics of primary Cr-spinel and olivine show that the protoliths were mainly harzburgite with minor dunite, with sparse massive chromitite bodies of various forms and sizes. Olivine inclusions in the chromitite lenses have higher forsterite content and NiO concentrations than fresh olivine relics in the host harzburgites and dunites, due to subsolidus re-equilibration. Cr-spinels in the chromitites have higher Cr# (0.74–0.82) than those hosted in dunite (0.72–0.76) or harzburgite (0.55–0.66). The scarce Cr-spinel crystals in harzburgite that have Cr# < 0.6 are interpreted to represent the population least affected by melt-rock interaction. The chromitite bodies are interpreted to have formed just below the contact between the oceanic crust and mantle sections (i.e., the petrologic Moho). The primary olivine (high Fo and Ni content) and Cr-spinel core compositions (high Cr# and low TiO2 content) of the Bir Tuluhah serpentinized peridotite are typical of modern supra-subduction zone (SSZ) fore-arc peridotites and consistent with crystallization from boninitic magma. The multistage petrogenesis leading to the chromitite bodies begins with moderate to high degrees of melt extraction from the protoliths of the serpentinized harzburgites, followed by reaction with melt compositions that evolved from tholeiite to boninite and left dunite residues. The massive Cr-rich chromitites in the Bir Tuluhah ophiolite are most probably the residues of such interaction between depleted harzburgite and ascending melts; mixtures of the reacted melts formed boninites, which became saturated with chrome-rich spinel and crystallized chromite pods before ascending past the Moho. We offer a novel thermodynamic model of this mixing and reaction process that quantifies the yield of Cr-spinel.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105968, title ="Genesis and geodynamic evolution of serpentinized ultramafics and associated magnesite deposits in the Al-Wask ophiolite, Arabian Shield, Saudi Arabia", author = "Gahlan, Hisham A. and Azer, Mokhles K.", journal = "American Journal of Science", volume = "320", number = "3", pages = "236-279", month = "March", year = "2020", doi = "10.2475/03.2020.02", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201009-131404911", note = "© 2020 American Journal of Science. \n\nSpecial thanks are paid to King Saud University, Deanship of Scientific Research, Research Group No. RG-1436-036, for their support. PDA acknowledges support from the US NSF, award EAR-1550934. The authors are grateful to Peter Kelemen and an anonymous reviewer for their insightful and constructive comments.", revision_no = "8", abstract = "Situated along the Yanbu Suture Zone, the Al-Wask ophiolite is one of the largest and best-preserved ophiolite sequences in the Proterozoic Arabian shield. A mantle section of serpentinized ultramafics is structurally overlain by a crustal section of gabbros and pillow lavas. The whole ophiolite sequence is capped by pelagic sedimentary cover, and tectonically emplaced over a metamorphosed island-arc volcano-sedimentary succession. The Al-Wask ultramafic rocks are strongly deformed, metamorphosed, and altered by carbonatization and silicification. Samples dominated by antigorite indicate upper greenschist to lower amphibolite facies peak metamorphic grade, whereas samples dominated by lizardite and magnesite preserve lower grade conditions that we interpret as a cooling path buffered to low CO₂ activity by the increasing stability of magnesite with decreasing temperature. Nearly all the primary silicate minerals have been replaced by serpentine minerals, leaving only relics of primary olivine and chromian spinel. Petrographic observation of relict olivine and spinel and of mesh and bastite textures in the serpentines suggest that the peridotite protoliths were mainly harzburgite with minor dunite. Whole-rock compositions of serpentinites show low CaO (<0.1 wt.%), Al₂O₃ (<1.5 wt.%), and Y (<0.4 ppm) combined with high Mg# (0.90–0.92), Ni, Co, and Cr contents; all these indicate a highly refractory mantle protolith. The mineral chemistry of relict primary spinel and olivine provides additional petrogenetic and geodynamic indicators. The high Cr# (> 60) and low TiO₂ (≤0.2 wt. %) of spinel and high forsterite contents (90–92) of associated olivine indicate residual mantle that underwent extensive partial melt extraction. The whole-rock and mineral chemistry of the serpentinized ultramafic rocks are both consistent with extracted melt fractions from ∼32 to 38 percent. This extent of melting is typical of fore-arc supra-subduction zone settings, which is the most likely tectonic environment for formation and preservation of the Al-Wask ophiolite.\nTwo types of magnesite deposits can be distinguished in the Al-Wask mantle section: an early generation of massive magnesite and a later generation of magnesite veins. Hence the Al-Wask ophiolite underwent multiple stages of carbonatization, likely involving different sources of CO₂-bearing fluids. The massive magnesite likely formed at relatively high temperature during cooling from peak metamorphic condition from CO₂-bearing fluid probably derived from decomposition of subducted carbonates. Using thermodynamic calculations in the simple MgO-SiO₂-H₂O-CO₂ system, we constrain the path of the reaction boundary where lizardite and magnesite can coexist at equilibrium. On the other hand, the cryptocrystalline magnesite veins fill tectonic fractures and likely formed at low temperature and shallow levels, after serpentinization and ophiolite obduction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100170, title ="Petrological characteristics of the Neoproterozoic Ess ophiolite mantle section, Arabian Shield, Saudi Arabia: a mineral chemistry perspective", author = "Gahlan, Hisham A. and Azer, Mokhles K.", journal = "International Journal of Earth Sciences", volume = "109", number = "1", pages = "239-251", month = "February", year = "2020", doi = "10.1007/s00531-019-01799-3", issn = "1437-3254", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191203-153418375", note = "© 2019 Geologische Vereinigung e.V. (GV). \n\nReceived 16 May 2019; Accepted 23 November 2019; First Online 03 December 2019. \n\nSpecial thanks are conveyed to King Saud University, Deanship of Scientific Research, Research Group No. RG-1436-036, for their support. PDA acknowledges support from the US NSF, award OCE-1826310. Comments by Prof. John Shervais (Utah State University, USA) and Ingo Braun improved the present version of the manuscript. Prof. Wolf-Christian Dullo (Editor-in-Chief) is acknowledged for editorial handling.", revision_no = "27", abstract = "The Ess ophiolite, one of the most important ophiolitic massifs of the Arabian Shield, consists of a lower succession of serpentinized mantle rocks overlain by an ultramafic cumulate sequence, layered and isotropic gabbros, sheeted dykes, pillow lavas and pelagic sediments. The Ess mantle section is composed mainly of serpentinized peridotites with chromitite pods, dunite, wehrlite and pyroxenite. Extensive metasomatism and alteration has transformed the ultramafic rocks to talc-carbonates, magnesite deposits and listvenite, especially along shear zones and fault planes. Nevertheless, relics of primary chromian spinel, olivine and pyroxenes are observed. Both primary and metamorphic olivines can be recognized in dunite; the latter is marked by very high forsterite content (97–98), low NiO content (<\u20090.2 wt%) and wide variations in MnO content (0.03–1.3 wt%). The mesh and bastite textures of the serpentine suggest that protoliths were mainly harzburgite with minor dunite. Some fresh cores of Cr-spinel are rimmed by ferritchromite and Cr-magnetite, indicating prograde metamorphism at lower amphibolite facies under oxidizing conditions. The high Cr# (>\u20090.6) and low TiO2 content (<\u20090.14 wt%) of fresh Cr-spinel and the high forsterite (0.90–0.93) and NiO contents (0.4–0.5 wt%) of fresh olivine are all consistent with residual mantle rocks that experienced high degrees of partial melt extraction. Orthopyroxene and clinopyroxene in the Ess peridotites have low CaO, Al₂O₃ and TiO₂ contents resembling those typically found in depleted harzburgites from fore-arcs. Consequently, we propose that the Ess mantle peridotites formed in a forearc setting during subduction initiation that developed as a result of northwest subduction due to the convergence between East and West Gondwana, leading eventually to closure of the Mozambique Ocean during the Pan-African orogeny.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100266, title ="High-pressure melt curve of shock-compressed tin measured using pyrometry and reflectance techniques", author = "La Lone, B. M. and Asimow, P. D.", journal = "Journal of Applied Physics", volume = "126", number = "22", pages = "Art. No. 225103", month = "December", year = "2019", doi = "10.1063/1.5132318", issn = "0021-8979", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191210-141558657", note = "© 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license\n(http://creativecommons.org/licenses/by/4.0/). \n\nSubmitted: 17 October 2019; Accepted: 25 November 2019; Published Online: 10 December 2019. \n\nWe are grateful for the help of Michael Burns, Russel Oliver, Ben Valencia, Mike Grover, Roy Abbott, Rick Allison, and Matthew Staska in performing the experiments. \n\nThis manuscript has been authored by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy and supported by the Site-Directed Research and Development Program, National Nuclear Security Administration, NA-10 USDOE NA Office of Defense Programs (NA-10). The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The U.S. Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or the United States Government. DOE/NV/03624–0470.", revision_no = "10", abstract = "We have developed a new technique to measure the melt curve of a shocked metal sample and have used it to measure the high-pressure solid-liquid phase boundary of tin from 10 to 30\u2009GPa and 1000 to 1800\u2009K. Tin was shock compressed by plate impact using a single-stage powder gun, and we made accurate, time-resolved radiance, reflectance, and velocimetry measurements at the interface of the tin sample and a lithium fluoride window. From these measurements, we determined temperature and pressure at the interface vs time. We then converted these data to temperature vs pressure curves and plotted them on the tin phase diagram. The tin sample was initially shocked into the high-pressure solid γ phase, and a subsequent release wave originating from the back of the impactor lowered the pressure at the interface along a constant entropy path (release isentrope). When the release isentrope reaches the solid-liquid phase boundary, melt begins and the isentrope follows the phase boundary to low pressure. The onset of melt is identified by a significant change in the slope of the temperature-pressure release isentrope. Following the onset of melt, we obtain a continuous and highly accurate melt curve measurement. The technique allows a measurement along the melt curve with a single radiance and reflectance experiment. The measured temperature data are compared to the published equation of state calculations. Our data agree well with some but not all of the published melt curve calculations, demonstrating that this technique has sufficient accuracy to assess the validity of a given equation of state model.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95382, title ="The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths", author = "Baziotis, I. and Xydous, S.", journal = "Geochimica et Cosmochimica Acta", volume = "266", pages = "307-331", month = "December", year = "2019", doi = "10.1016/j.gca.2019.04.024", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190509-151839952", note = "© 2019 Elsevier Ltd. \n\nReceived 8 December 2018, Revised 24 April 2019, Accepted 24 April 2019, Available online 9 May 2019. \n\nWe thank the constructive comments raised by Dr. Anne Peslier, Dr. Emily J. Chin and an anonymous reviewer. Also, we are grateful to the associate editor Dr. James Day for his editorial handling and fruitful review. I.B. obtained funds for this research from the Action «Supporting Postdoctoral Researchers» of the Operational Program “Education and Lifelong Learning” of the General Secretariat for Research and Technology, co-financed by the European Social Fund (ESF) and the Greek State. I.B. and S.K. acknowledge the IKYDA academic exchange program between the Greek State Foundation and the Deutscher Akademischer Austauschdienst – DAAD. PDA is supported by the US NSF through award GI-1550934. I.B. would like to thank Theo Ntaflos for support with the electron probe microanalyses. This paper is dedicated to Larry Augustus Taylor, with deep respect from all the authors for his many long-lasting contributions to the study of terrestrial, lunar, and martian rocks. I.B. wishes to express what a great honor and inspiration it was to work with Larry as a postdoc and to have learned meteoritics and mantle xenolith studies from such a distinguished scientist.", revision_no = "16", abstract = "We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/98790, title ="Mid-Neoproterozoic mafic rocks in the western Jiangnan orogen, South China: Intracontinental rifting or subduction?", author = "Wan, Le and Zeng, Zuoxun", journal = "Journal of Asian Earth Sciences", volume = "185", pages = "Art. No. 104039", month = "November", year = "2019", doi = "10.1016/j.jseaes.2019.104039", issn = "1367-9120", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190923-095416677", note = "© 2019 Elsevier Ltd. \n\nReceived 29 March 2019, Revised 15 September 2019, Accepted 22 September 2019, Available online 23 September 2019.", revision_no = "9", abstract = "Widely distributed Meso- to Neoproterozoic igneous rocks record the evolution of the Jiangnan orogen. We present integrated geochemical and geochronological data for basalts from the Gaoqiao area, northwestern Hunan Province. U-Pb dating of zircons indicates that the formation of Gaoqiao basalts occurred in the Neoproterozoic, no earlier than 757 ± 16 Ma. Like the contemporaneous mafic rocks in neighboring areas, the Gaoqiao basalts show trace element characteristics suggesting derivation from a source similar to ocean-island basalts (OIBs), including strong enrichment in large-ion lithophile elements (LILEs), high-field strength elements (HFSEs) and TiO_2, and high Ti/Y ratios. Placed in a regional tectonic context, however, the Gaoqiao suite is most consistent with an intracontinental rift model and offers no support to the idea of ongoing subduction in middle-late Mid-Neoproterozoic time in the western Jiangnan orogen. Despite the coincidence between the age of this rift and the separation of East Antarctica-Australia from Laurentia, we argue that the rift recorded in the South China Block (SCB) was an independent and probably unrelated event during the break-up of the Rodinia supercontinent.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99087, title ="Geochemistry and Petrogenesis of Late Ediacaran Rare-metal Albite Granites of the Arabian-Nubian Shield", author = "Abu Amarah, Bassam A. and Azer, Mokhles K.", journal = "Acta Geologica Sinica - English Edition", month = "October", year = "2019", doi = "10.1111/1755-6724.14379", issn = "1000-9515", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191004-111939202", note = "© 2019 Wiley. \n\nAccepted manuscript online: 03 October 2019.", revision_no = "5", abstract = "The Abu Dabbab albite granite (ADAG), in the central Eastern Desert of Egypt, hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian‐Nubian Shield. Here, we report detailed field, petrographic, mineralogical and geochemical investigation of the ADAG, an isolated stock‐like granitic body with sharp intrusive contacts against metamorphic country rocks, probably emplaced at about 600 Ma. The fine‐grained porphyritic upper unit is a preserved remnant of the shallowly‐emplaced apex of the magma chamber, whereas the medium‐grained lower unit crystallized at deeper levels under subvolcanic conditions. The peraluminous leucocratic ADAG shares common geochemical characteristics with post‐collisional intraplate A‐type magmas. In addition to the conspicuous enrichment in Na_2O, the ADAG is remarkable for its anomalous concentrations of Ta, Nb, Li, Hf, Ga, Sn, Zn and heavy rare‐earth elements. Nb‐Ta minerals in the ADAG are mixed with Fe‐Mn oxides, forming black patches that increase in abundance toward of the base of the intrusion. Columbite–tantalite, cassiterite and wolframite are the most important ore minerals. Pronounced negative Eu anomalies (Eu/Eu* = 0.10–0.24) reflect extreme magmatic fractionation and perhaps the effects of late fluid‐rock interaction. The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness. Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes, late‐stage metasomatism caused limited redistribution of rare metals. Fluid‐driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen, amazonite, and quartz veins along fracture systems.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95102, title ="Geochemistry of middle-late Mesozoic mafic intrusions in the eastern North China Craton: New insights on lithospheric thinning and decratonization", author = "Wan, Le and Zeng, Zuoxun", journal = "Gondwana Research", volume = "73", pages = "153-174", month = "September", year = "2019", doi = "10.1016/j.gr.2019.04.004", issn = "1342-937X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190430-075323548", note = "© 2019 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. \n\nReceived 26 January 2019, Revised 20 March 2019, Accepted 7 April 2019, Available online 24 April 2019.", revision_no = "10", abstract = "We present detailed geochronological, geochemical and Sr-Nd-Pb isotopic data for late Mesozoic mafic intrusions in the Taili region (western Liaodong Province) of the eastern North China Craton (NCC). We obtained laser-ablation inductively-coupled plasma mass spectrometry U-Pb zircon ages from lamprophyres with ages ranging from 139 to 162\u202fMa and diorites with clusters of ages at 226\u202f±\u202f11\u202fMa, 165\u202f±\u202f5.8\u202fMa and 140\u202f±\u202f4.8\u202fMa. We interpret the Triassic zircons in diorites to be inherited from the Paleo-Asian Ocean slab. Both the lamprophyres and diorites contain abundant inherited grains (2644–2456\u202fMa) that were likely derived from the ancient NCC basement, reflecting a contribution from old lower crustal material. Like contemporaneous late Mesozoic mafic rocks in the Jiaodong and Liaodong Peninsula areas of the NCC, the Taili lamprophyres reveal a strong subduction signature in their normalized trace element patterns, including depletion of high field strength elements and enrichment of large ion lithophile elements. The rare-earth element patterns of the Taili intermediate-mafic intrusions are best explained if they were principally derived from partial melting of amphibole-bearing lherzolite in the spinel-garnet transition zone. Slab-derived melts likely contributed to the formation of late Mesozoic mafic rocks along three margins of the craton: due to accretion of the Yangtze Block along the southern margin of the craton, subduction of the Paleo-Asian Ocean along the northern margin, and subduction of the Paleo-Pacific oceanic plate along the eastern margin of NCC. We present a synthesis of the geochemical, spatial, and temporal patterns of magmatic rocks and periods of deformation that contributed to decratonization of the NCC in response to the Mesozoic tectonic evolution of adjacent plates along its northern, southern, and eastern margins.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/93200, title ="Santorini volcano as a potential Martian analogue: The Balos Cove Basalts", author = "Pantazidis, A. and Baziotis, I.", journal = "Icarus", volume = "325", pages = "128-140", month = "June", year = "2019", doi = "10.1016/j.icarus.2019.02.026", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190225-085123402", note = "© 2019 Elsevier Inc. \n\nReceived 31 October 2018, Revised 18 February 2019, Accepted 22 February 2019, Available online 25 February 2019. \n\nWe thank the constructive comments raised by two anonymous reviewers and the editor Dr. Johnson for his editorial handling. Also, we kindly thank Dr. Scott VanBommel for his great help with the handling of the PDS geosciences node data. We greatly thank Dr. G. Economou from Institute of Geology and Mineral Exploration (Athens, Greece) for access on their SEM and XRD facilities. Also, we thank Dr. C. Anagnostou for his efforts to perform the XRF analyses at the Hellenic Centre for Marine Research (HCMR). We acknowledge Dr. Jesús Martinez-Frias for his kindness to review an early version of the manuscript.", revision_no = "15", abstract = "The interpretation of geologic processes on Mars from sparse meteorite, remote sensing and rover data is influenced by knowledge gained from well-characterized terrestrial analogues. This calls for detailed study of candidate terrestrial analogues and comparison of their observable features to those encountered on the surface of Mars. We evaluated the mineralogical, geochemical, and physical properties of the Balos cove basalts (BCB) from the island of Santorini and compared them to Martian meteorites, Mars rover surface measurements, and other verified Martian analogues obtained from the International Space Analogue Rockstore (ISAR). Twenty rock samples were collected from the Balos cove area based on their freshness, integrity, and basaltic appearance in the field. Optical microscopy of BCB revealed a pilotaxitic to trachytic texture, with olivine and clinopyroxenephenocrysts in a fine groundmass of olivine, clinopyroxene, plagioclase, magnetite, and devitrified glass. All major minerals show normal zoning, including calcic plagioclase (An_(78–85) at the core and An_(60–76) at the rim), augite (En_(36-48)Wo_(41-44)Fs_(11–21)), and olivine (Fo_(74–88)). The dominant bands in the infrared-attenuated total reflectance (IR-ATR) spectra from BCB can be assigned to olivine (~875\u202fcm−1), calcic plagioclase (~1130\u202fcm^(−1)), and augite (~970\u202fcm^(−1)). The whole-rock chemical compositions and mineralogy of the BCB are similar to published analyses of typical olivine-phyric shergottites and basalts and basaltic materials analyzed in Gusev and Gale craters on Mars. BCB porosity is in the range of 7–15% and is similar to the porosities of the ISAR samples. Although no terrestrial rock is ever a perfect match to Martian compositions, the differences in mineralogy and geochemistry between BCB and some classes of Martian samples are relatively subtle and the basalts of Santorini are as close a match as other accepted Mars basalt analogues. The Santorini site offers excellent field logistics that, together with the petrology of the outcrop, makes it a valuable locality for testing and calibration deployments, field training, and other activities related to current and future Mars exploration.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94659, title ="Application of Al-Cu-W-Ta graded density impactors in dynamic ramp compression experiments", author = "Kelly, James P. and Nguyen, Jeffrey H.", journal = "Journal of Applied Physics", volume = "125", number = "14", pages = "Art. No. 145902", month = "April", year = "2019", doi = "10.1063/1.5055398", issn = "0021-8979", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190411-120804967", note = "© 2019 Author(s). Published under license by AIP Publishing. \n\nSubmitted: 7 September 2018 · Accepted: 26 March 2019 ·\nPublished Online: 11 April 2019 \n\nThis work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. The authors would also like to thank Ernest Bianchi at Maryland Ceramic & Steatite Company, Inc., for tape casting services, Renee Posadas, J. Castellanos, Joshua Ruelas, and Paul Benevento at the Lawrence Livermore National Laboratory for assistance with characterization and fabrication of the impactors, Sharon Torres and James Embree for assistance with metallography, Bob Nafzinger for target fabrication, and Michael J. Burns and Russel Oliver for assistance with the Light Gas Gun experiment. Collaboration with the Caltech Lindhurst Laboratory for Experimental Geophysics is supported by LLNL subcontract B621015.", revision_no = "10", abstract = "Graded density impactors (GDIs) are used to dynamically compress materials to extreme conditions. Two modifications to a previously developed Mg-Cu-W GDI are made in this work before using it in a dynamic compression experiment: Mg is replaced with Al and a Ta disk is glued to the back. The Mg phase is replaced by Al because FCC Al remains solid to higher pressure along its Hugoniot compared to Mg. The addition of the Ta disk creates a constant particle velocity regime and facilitates a definition of peak pressure states. Microstructure analysis, profilometry, and ultrasonic C-scans of the Al-Cu-W GDI all confirm excellent uniformity. We evaluated signal variation in the radial direction of a dynamically compressed Al-LiF bilayer target to evaluate the contribution of spatial nonuniformity to errors. Velocity traces from five photon Doppler velocimetry (PDV) probes located at different radial distances from the center of the target varied at most by 1.1% with a root mean square of 0.3% during the compression ramp, demonstrating low PDV measurement error over a relatively large experimental area. The experimental PDV data also agrees well with 1D simulations that use inputs from predictive characterization models developed for the material properties resulting from tape casting, laminating, and powder consolidation processes. Low measurement error during quasi-isentropic compression, leading to better precision, ensures a robust platform to reach extreme compression and low-temperature recovery states and facilitates discovery via synthesis, quenching, and preservation of new high-pressure phases.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95169, title ="Tantalum sound velocity under shock compression", author = "Akin, Minta C. and Nguyen, Jeffrey H.", journal = "Journal of Applied Physics", volume = "125", number = "14", pages = "Art. No. 145903", month = "April", year = "2019", doi = "10.1063/1.5054332", issn = "0021-8979", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190502-102042764", note = "© 2019 Published under license by AIP Publishing. \n\nSubmitted: 30 August 2018; Accepted: 21 March 2019; Published Online: 11 April 2019. \n\nWe thank P. Rigg, P. Söderlind, and J. Klepeis for useful discussions, and the editors and reviewers for their work to improve this paper. We thank Papo Gelle, Mike Long, Russ Oliver, Mike Burns, Toni Bulai, Bob Nafzinger, Paul Benevento, Sam Weaver, and Cory McLean for their excellent and dedicated work. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract No. DE-AC52-07NA27344.", revision_no = "12", abstract = "We used several variations of the shock compression method to measure the longitudinal sound velocity of shocked tantalum over the pressure range 37–363\u2009GPa with a typical uncertainty of 1.0%%. These data are consistent with Ta remaining in the bcc phase along the principal Hugoniot from ambient pressure to ≈300\u2009GPa, at which pressure melting occurs. These data also do not support the putative melting phenomena reported below 100\u2009GPa in some static compression experiments.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94393, title ="Crystal size distribution of amphibole grown from hydrous basaltic melt at 0.6–2.6 GPa and 860–970 °C", author = "Zhang, Bo and Hu, Xianxu", journal = "American Mineralogist", volume = "104", number = "4", pages = "525-535", month = "April", year = "2019", doi = "10.2138/am-2019-6759", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190403-085027141", note = "© 2019 Mineralogical Society of America.\n\nFunding:\nThis work benefited from the financial support of the National Natural Science Foundation of China (Grant No. 41772043 and 41802043), the Joint Research Fund in Huge Scientific Equipment (U1632112) under cooperative agreement between NSFC and CAS, the Chinese Academy of Sciences “Light of West China” Program (Dawei Fan, 2017), Youth Innovation Promotion Association CAS (Dawei Fan, 2018434), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB 18010401), the CPSF-CAS Joint Foundation for Excellent Postdoctoral Fellows (Grant No. 2017LH014), and China Postdoctoral Science Foundation (Grant No. 2018M631104). Experiments in the Caltech lab and participation of PDA in this work were supported by the U.S. NSF through award EAR-1550934.\n\nThe authors thank Michael Zieg and Michael Higgins for their very insightful and thorough reviews, and sincere thanks are extended to Associate Editor Erik Klemetti. We thank Hongfeng Tang for providing the important diorite sample, Neng Jiang for his assistance during EMP analyses. We warmly thank Yijin Yang and Wei Mao for their linguistic assistance during the preparation of this manuscript.", revision_no = "12", abstract = "We carried out three series of amphibole crystallization experiments from hydrous basaltic melt to calibrate the dependence of crystal growth rate on temperature and pressure in amphibole-bearing igneous rocks. One series of 100 h duration multi-anvil experiments were carried out at a constant pressure of 0.6 GPa and variable temperatures from 860 to 970 °C. The second series was conducted at a constant temperature of 970 °C and variable pressures from 0.6 to 2.6 GPa. The third series examined the time dependence at 970 °C and 0.6 GPa, with durations from 1 to 100 h. A verification experiment showing both reproducibility and the ability of these three series to predict behavior at novel conditions was performed in a piston cylinder at 1.0 GPa and 900 °C for 63 h. All experiments yielded mostly amphibole in a quenched glass of granitic to granodioritic composition. We used the two-dimensional thin section method to measure the crystal size distribution (CSD) of amphibole in the experimental products. Concave-down CSD curves at small sizes indicate a textural coarsening process during the crystallization. The CSD data were inverted using canonical CSD theory for CSD growth rate; maximum and average growth rates of amphibole were also inferred directly from the maximum and average grain size and crystallization time. The maximum growth rate is, of course, always larger than the average growth rate, which is in turn slightly larger than the CSD growth rate, suggesting that CSD growth rate is an adequate measure of the average growth rate of a mineral in magmatic rocks. The CSD growth rate increases with increasing temperature in the isobaric series and with increasing pressure at constant temperature. However, the growth rate is negatively correlated with crystallization time at constant temperature and pressure. Based on the experimental results, a functional form for evaluating growth rate at known pressure and temperature from an observed amphibole CSD was developed and applied to a diorite collected from the eastern Tianshan Mountains, Xinjiang Uygur autonomous region, NW China. The estimated growth rate of amphibole is between 1.6 × 10^(–9) mm/s and 5.6 × 10^(–7) mm/s, and combined with petrological constraints on pressure and temperature, the corresponding crystallization time was between 0.1 and 4.3 yr in the natural diorite.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/92406, title ="Hydrothermal scavenging of ^(230)Th on the Southern East Pacific Rise during the last deglaciation", author = "Lund, David C. and Pavia, Frank J.", journal = "Earth and Planetary Science Letters", volume = "510", pages = "64-72", month = "March", year = "2019", doi = "10.1016/j.epsl.2018.12.037", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190123-072432500", note = "© 2019 Elsevier B.V. \n\nReceived 28 August 2018, Revised 23 December 2018, Accepted 28 December 2018, Available online 18 January 2019. \n\nDCL, EIS, and SM were supported by NSF award OCE-1558641 and the UCONN Research Excellence Program. We are grateful to David Cady at UCONN for assistance with ICP-MS analyses, Jean Lynch-Stieglitz at Georgia Tech for assistance with stable isotope analyses, and Martin Fleisher at LDEO for assistance with ^(230)Th and ^(231)Pa analyses. We are also indebted to the Oregon State University Core Repository for the curation of core OC73-3-20. The OSU Repository is supported by NSF award OCE-1558679. PDA was supported by NSF awards OCE-1558372 and EAR-1551433. FJP was supported by an NSF-GRFP(DGE-16-44869). All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials.", revision_no = "24", abstract = "Thorium-230 (^(230)Th) is a fundamental tool for estimating sediment fluxes in the open ocean. Because ^(230)Th is rapidly scavenged by particles falling through the water column, the flux of ^(230)Th to underlying sediments is typically equal to its water column production rate. However, recent surveys suggest hydrothermal plumes are unusually efficient scavengers of ^(230)Th. Here we show that hydrothermal scavenging on the Southern East Pacific Rise (SEPR) resulted in ^(230)Th fluxes several times higher than the water column production rate during the last deglaciation. Elevated fluxes likely require diffusive transport of dissolved ^(230)Th from the ridge flanks towards the ridge crest. Depending on the length-scale of ^(230)Th transport, the resulting deficits in ^(230)Th may yield overestimates of sediment flux to ridge flank sediments. We also show that Fe fluxes at 19°S on the SEPR lag those at 11°S and 6°S by several thousand years, inconsistent with a signal driven by changes in deep water pH and oxygen levels. Instead, variable hydrothermal activity is the simplest explanation of the observed signals in the Pacific, Indian, and Atlantic basins.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/92335, title ="Multiple Stages of Carbonation and Element Redistribution during Formation of Ultramafic-Hosted Magnesite in Neoproterozoic Ophiolites of the Arabian-Nubian Shield, Egypt", author = "Azer, Mokhles K. and Gahlan, Hisham A.", journal = "Journal of Geology", volume = "127", number = "1", pages = "81-107", month = "January", year = "2019", doi = "10.1086/700652", issn = "0022-1376", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190117-083853716", note = "© 2018 by The University of Chicago. \n\nManuscript received April 14, 2018; accepted September 13, 2018; electronically published December 7, 2018. \n\nWe acknowledge the logistical support provided by the Geological Sciences Department–National Research Centre, Egypt. P. D. Asimow acknowledges support from the US National Science Foundation, award EAR-1551433. We extend our appreciation to the Deanship of Scientific Research, King Saud University, for supporting this work through research group RG-1436-036. Special thanks to C. Ma for his help with the microprobe analyses.", revision_no = "12", abstract = "We present a study of the serpentinized peridotites of the Ghadir-Mohagar-Ambaut area, Egypt. They represent the mantle section of a dismembered ophiolite, tectonically emplaced over a volcanosedimentary succession of island arc assemblages. The serpentinites are variably metamorphosed from greenschist to lower-amphibolite facies, metasomatized, and altered, including development of talc-carbonate and quartz-carbonate rocks, especially along shear zones and fault planes. Nevertheless, some samples contain relics of primary chromian spinel, olivine, and pyroxenes. Relict textures and whole-rock compositions (Mg#[molar Mg/(Mg+Fe^(2+))]=0.92–0.93, with low Al_2O_3 and CaO contents) both suggest harzburgite protoliths. The high Mg# and Ni contents of relict olivine and the high Cr# (molar Cr/(Cr+Al)molar Cr/(Cr+Al)) of fresh chromian spinel cores indicate that the protoliths experienced high degrees of partial melt extraction (∼34%–39%), well beyond the limit for exhaustion of clinopyroxene from the residue and consistent with formation in a forearc suprasubduction zone environment. The serpentinized ultramafic rocks in the study area are divided into massive serpentinite, serpentinite-hosted magnesite masses, and magnesite-filled veins. The carbonation and formation of magnesite ores took place through two metasomatic stages; the first is represented by the magnesite masses and associated with deep-seated metasomatism and alteration during serpentinization, whereas the second, vein-forming stage postdates serpentinization and occurred during obduction of the ophiolite. The differences in chemical composition between massive serpentinite and serpentinite-hosted magnesite masses suggest leaching of some elements and enrichment of others during carbonation; MgO, Cr, and Ni are depleted, whereas Fe_2O_3, CaO, MnO, Nb, Ba, Cu, Pb, Sr, and Zn are enriched in the serpentinite-hosted magnesite masses, relative to the host massive serpentinite.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91882, title ="The common origin and alteration history of the hypabyssal and volcanic phases of the Wadi Tarr albitite complex, southern Sinai, Egypt", author = "Azer, Mokhles K. and Gahlan, Hisham A.", journal = "Lithos", volume = "324-325", pages = "821-841", month = "January", year = "2019", doi = "10.1016/j.lithos.2018.12.015", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181218-082623531", note = "© 2018 Published by Elsevier B.V. \n\nReceived 5 August 2018, Accepted 14 December 2018, Available online 18 December 2018. \n\nPDA and the development of the alphaMELTS2 interface to rhyoliteMELTS were funded by the US National Science Foundation through award EAR-1550934. The authors extend their appreciation to the Deanship of Scientific Research, King Saud University, for supporting this work through research group no. (RG-1436-036). We thank Craig Lundstrom for an exceptionally thoughtful review. We are also indebted to Prof. Nelson Eby (Editor in Chief) for numerous helpful comments.", revision_no = "18", abstract = "New data and interpretations are presented for the igneous albitites of the Wadi Tarr area, southern Sinai, Egypt. The albitite masses are isolated in outcrop from any granitic intrusions and have intrusive contacts against the country rocks without any structural control. They have marginal zones of breccias with jigsaw-fit angular clasts suggesting explosive, in-situ formation. The albitites are of two types: the western, medium-grained, hypabyssal albitite and the eastern, fine-grained porphyritic albitite. The field relations suggest emplacement at different levels in a magmatic cupola: the hypabyssal texture and steeply dipping slope of the upper contact of the western albitite imply deeper emplacement whereas the gently dipping contacts and porphyritic texture of the eastern albitite masses indicate that they define the probable location of the cupola apex. Both types of albitites consist of albite (92–97%) with minor amounts of quartz, K-feldspar and biotite. The accessory minerals include Fe-oxides, augite, sulphides, zircon, rutile, xenotime, titanite, allanite and monazite. The whole-rock compositions of the hypabyssal and porphyritic albitites are closely related, but the porphyritic type has lower abundances of Sr, Ba, Y, Nb, Th and Zr. We show that the hypabyssal and porphyritic albitites have a common petrogenetic origin, most likely as late-stage cumulates from a fractionating, strongly alkaline A-type magma, consistent with the compositions of the mafic minerals. The source magma was probably a tephritic liquid; we use MELTS models to show that only a sufficiently alkaline magma follows a differentiation path that both avoids quartz saturation and encounters the alkali feldspar solvus, reaching a residual liquid in equilibrium with highly sodic feldspar. Although the MELTS results show a chemically consistent means of forming igneous albitite, they are incomplete in that physical segregation mechanisms are still required to isolate the albite from mafic minerals and or a low-temperature aqueous alteration stage is needed to leach K from the feldspar. Alteration surrounding the Wadi Tarr albitites is extensive and dominated by alkali metasomatism similar to fenitization. Alteration in the marginal breccia zone of the albitite is dominated by precipitation of amphibole and carbonate in veins and in the breccia matrix, whereas the volcanic country rocks show replacement of feldspars by sericite, carbonate and epidote as well as vein carbonate. The altered volcanic country rocks show lower concentrations of Fe_2O_3, Sr, Cu, Pb, Ba and Ce, accompanied by higher concentrations of Na2O and MgO compared to unaltered equivalent samples.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/89161, title ="Seconds after impact: Insights into the thermal history of impact ejecta from diffusion between lechatelierite and host glass in tektites and experiments", author = "Macris, Catherine A. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "241", pages = "69-94", month = "November", year = "2018", doi = "10.1016/j.gca.2018.08.031", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180827-094621796", note = "© 2018 Elsevier. \n\nReceived 29 March 2017, Revised 15 August 2018, Accepted 17 August 2018, Available online 25 August 2018. \n\nThe authors would like to acknowledge NASA grants NNX12AH63G and NNX15AH37G for funding this study. J.B. acknowledges the financial support of the UnivEarthS Labex program at Sorbonne Paris Cite (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02) and the IPGP multidisciplinary program PARI, and by Paris-IdF region SESAME Grant no. 12015908. We also thank Peter Goldreich and Megan Newcombe for insightful discussions and modeling advice. Thanks to John Shukle for his coding expertise and time. Chi Ma’s help was invaluable in obtaining the electron probe data. This manuscript was greatly improved by the comments of Mathias Ebert and two anonymous reviewers.", revision_no = "18", abstract = "Tektites contain inclusions of lechatelierite, nearly pure SiO_2 glass formed by quenching of quartz grains melted during hypervelocity impacts. We report the discovery in a tektite of chemically zoned boundary layers (ca 20\u202fμm) between lechatelierite and host felsic glass. These boundary layers in tektites formed by chemical diffusion between molten silicainclusions (quenched to lechatelierite on cooling) and surrounding felsic melt. We reproduced the details of these boundary layers via experiments on mixtures of powdered natural tektite plus quartz grains heated to 1800–2400\u202f°C for 1–120\u202fs using an aerodynamic levitation laser heating furnace. The results of these experiments were used to provide quantitative constraints on possible thermal histories of the natural sample.\nThe experiments successfully reproduced all major aspects of the concentration profiles from the natural sample including diffusion length scale, strong asymmetry of the concentration profiles with respect to the Matano plane (due to the strong concentration dependence of the diffusivities of all oxides on SiO_2 content), similarities in lengths of the diffusive profiles (due to control by the diffusion of SiO_2 on the diffusivity of the other oxides), and differences in the shapes of the profiles among the oxides (including a maximum in the diffusion profile of K_2O due to uphill diffusion). The characteristic lengths of all non-alkali oxide profiles are proportional to t from which diffusivities and activation energies can be derived; these results are consistent with measurements in melts with lower SiO_2 contents and at lower temperatures reported in the literature. We also fit the experimental profiles of SiO_2 and Al_2O_3 using simple formulations of the dependence of their diffusivities on SiO_2 content and temperature, yielding results similar to those obtained from the t dependence of the characteristic profile lengths.\nThe quantitative characterization of diffusion in boundary layers based on our experiments allow us to set limits on the thermal history of the natural tektite in which the boundary layers were discovered. If the interdiffusion between the silica and felsic melts occurred at constant temperature, the duration of heating experienced by the natural tektite we studied depends on temperature; possible solutions include heating at ∼2000\u202f°C for ∼70\u202fs, −2400\u202f°C for ∼3 s. We also explored non-isothermal, asymptotic cooling histories; for a maximum temperature of 2400\u202f°C, a characteristic cooling time scale of ∼50\u202fs is implied, whereas, for 2000\u202f°C, the time scale is ∼1400\u202fs. Further, a maximum temperature of ∼2360\u202f°C yields an effective diffusive time scale of ∼5\u202fs, a cooling time scale of ∼90\u202fs, and a cooling rate at the glass transition temperature of ∼5\u202f°C/s; results that are consistent with independent estimates of cooling time scales for ∼1\u202fcm clasts (Xu and Zhang, 2002), as well as cooling rates at the glass transition temperature (Wilding et al., 1996) – thus satisfying all currently available relevant data. More complex T-t paths are possible and can also be modeled using our experimental results and compared with and used as tests of the accuracy of physical models of tektite-forming impact events.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91313, title ="Formation and Evolution of a Magmatic System in a Rifting Continental Margin: Neoproterozoic Arc- and MORB-like Dike Swarms in South China", author = "Zhao, Jun-Hong and Asimow, Paul D.", journal = "Journal of Petrology", volume = "59", number = "9", pages = "1811-1844", month = "September", year = "2018", doi = "10.1093/petrology/egy080", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181128-143703302", note = "© The Author(s) 2018. Published by Oxford University Press. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) \n\nReceived January 5, 2018; Accepted August 2, 2018. \n\nThis work was substantially supported by the National Nature Science Foundation of China (41073026, 41373016, 41573020) and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan). PDA was supported in part by the US National Science Foundation through award GI-1226270.", revision_no = "22", abstract = "Mafic magmas generated in extensional tectonic settings preserve important information about the nature of their mantle sources, interactions between crust and mantle, and the processes associated with magmatic evolution. However, careful study is needed to interpret the complex petrogenesis and diverse origins of such rock suites. A large volume of c.650\u2009Ma mafic and ultramafic dikes are found in the South Qinling Belt (SQB) along the northern margin of the Yangtze Block, South China. The dikes from the eastern SQB are composed of olivine gabbro and gabbro that have low SiO_2 (42·60 to 49·56\u2009wt %), low K_2O+Na_2O (0·98 to 4·48\u2009wt %), and high MgO (4·96 to 14·41\u2009wt %). MELTS modeling reveals that many of these dikes could have originated from a common primary magma that underwent extensive fractional crystallization of olivine + plagioclase + clinopyroxene followed by accumulation of phenocrysts in most samples. They show arc-like trace element compositions characterized by enrichment of LILE and LREE and depletion of HFSE. They have high initial ^(87)Sr/^(86)Sr (0·705192 to 0·706622), negative εNd_(650) (-7·11 to -4·45), and very low ^(206)Pb/^(204)Pb (16·71 to 16·98), ^(207)Pb/^(204)Pb (15·36 to 15·42) and ^(208)Pb/^(204)Pb (37·17 to 37·48). Their magmatic zircons preserve relatively homogeneous δ^(18)O (+4·95‰ to +6·41‰) and highly variable εHf (-0·5 to +10·0). Both chemical compositions and modeling results suggest that dikes from the eastern SQB were derived from a lithospheric mantle source that had been extensively modified by earlier subduction and further underwent strong contamination by the ancient granulite facies lower crust. In contrast, mafic dikes from the western SQB have relatively high SiO_2 (44·97 to 52·09\u2009wt %) and low MgO (4·73 to 9·40\u2009wt %). They fall into two groups that show N-MORB and E-MORB-like elemental characteristics, respectively. Both types have low initial ^(87)Sr/^(86)Sr (0·703752 to 0·706850), positive εNd_(650) (+2·75 to +5·85) and scattered ratios of ^(206)Pb/^(204)Pb (17·25 to 18·42), ^(207)Pb/^(204)Pb (15·44 to 15·55) and ^(208)Pb/^(204)Pb (37·37 to 38·74). Their zircon δ^(18)O (+3·64‰ to +5·33‰) and εHf (+10·2 to +14·8) values are also significantly different from those of the eastern SQB dikes. The chemical evidence suggests that mafic dikes from the western SQB originated from a heterogeneous asthenospheric mantle, one part of which may have been enriched by OIB/seamount subduction. These mafic dikes underwent only minor modification in the lower crust, but are contaminated by high temperature hydrothermally-altered supracrustal materials. Generation of the voluminous mafic and ultramafic dikes in the SQB occurred in a rifting continental margin after a long period of subduction. Their diverse origins and complex geodynamic setting suggest that magmatism in rifting continental margins is not only controlled by the structure of the lithosphere and upwelling of the asthenospheric mantle, but also by interaction between melts and continental crust. The mafic–ultramafic dikes in this study further indicate that an active magma plumbing system may have evolved beneath a ‘non-volcanic’ passive continental margin.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88350, title ="Geophysical source conditions for basaltic lava from Santorini volcano based on geochemical modeling", author = "Baziotis, Ioannis and Kimura, Jun-Ichi", journal = "Lithos", volume = "316-317", pages = "295-303", month = "September", year = "2018", doi = "10.1016/j.lithos.2018.07.027", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180730-095303577", note = "© 2018 Elsevier B.V. \n\nReceived 26 April 2018, Accepted 26 July 2018, Available online 30 July 2018. \n\nJ.I.-K. was funded by JSPS KAKENHI grant #JP15H02148, #JP16H01123, and #JP18H04372. PDA's participation in this study was funded by the US NSF, award EAR-1550934. We are grateful for the editorial handling by Andrew Kerr, and the fruitful comments made by two anonymous reviewers.", revision_no = "17", abstract = "Santorini volcano sits ~145\u202fkm above the Aegean Wadati-Benioff zone, where the African plate subducts northward beneath Eurasia. There are only a few localities in the whole Aegean where basaltic lavas primitive enough to constrain mantle processes beneath the Aegean arc can be found; in this work we analyzed one such locality, a basalt lava from the southern part of Santorini. We apply a suite of petrological tools (PRIMACALC2 and ABS5) in sequence to estimate magma chamber conditions, primary magma composition, mantle melting conditions, and slab dehydration conditions. Back-calculation modeling based on major-element chemistry yields shallow magma chamber conditions of P\u202f=\u202f0.02\u202fGPa, fO_2\u202f=\u202fQFM\u202f+\u202f2, and ~1\u202fwt% H_2O in the primary magma. The estimated major element composition of this primary magma then leads to estimated mantle melting conditions of 2.1\u202fGPa, 1353\u202f°C, and F\u202f=\u202f8%; whereas a more precise estimate derived from trace elementmodeling implies 1.7\u202fGPa, 1323\u202f°C, and F\u202f=\u202f18%. Furthermore, the trace element model implies a slab flux derived from 4.6\u202fGPa (~150\u202fkm slab depth). The estimated slab depth, magma segregation conditions, and magma chamber depth are all consistent with seismic observations, supporting slab dehydration in the seismically imaged steep slab interval and flux melting in a relatively hot mantle wedge.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87337, title ="Late‐Cretaceous construction of the mantle lithosphere beneath the central California coast revealed by Crystal Knob xenoliths", author = "Quinn, D. P. and Saleeby, J. B.", journal = "Geochemistry, Geophysics, Geosystems", volume = "19", number = "9", pages = "3302-3346", month = "September", year = "2018", doi = "10.1029/2017GC007260", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180626-072857286", note = "© 2018 American Geophysical Union. \n\nReceived 26 SEP 2017; Accepted 5 MAY 2018; Accepted article online 23 JUN 2018; Published online 21 SEP 2018; Corrected 21 OCT 2018. \n\nThis article was corrected on 21 OCT 2018. See the end of the full text for details. \n\nWe would like to thank M. Cosca and the USGS Argon geochronology laboratory for their assistance with dating the Crystal Knob basalt flow. J. Blundy and M. Gurnis were valuable resources on REE thermometry and geodynamic modeling, respectively. F. Sousa and J. Price encouraged consideration of the wider tectonic context. We would also like to thank A. Chapman, E. Nadin, and one anonymous reviewer for their excellent feedback, which greatly improved this contribution. This work was supported by the Caltech Tectonics Observatory and funded by the Gordon and Betty Moore Foundation through grant GBMF423.01. A PostgreSQL database containing analytical data and modeling results is archived with CaltechDATA at DOI 10.22002/D1.320. Data reduction, modeling, and graphics compilation code is at 10.22002/D1.321.", revision_no = "22", abstract = "The Pleistocene (1.65 Ma) Crystal Knob volcanic neck in the California Coast Ranges is an olivine‐plagioclase phyric basalt containing dunite and spinel peridotite xenoliths. Crystal Knob erupted through the Nacimiento belt of the Franciscan complex and adjacent to Salinian crystalline nappes. Its xenoliths sample the mantle lithosphere beneath the outboard exhumed remnants of the southern California Cretaceous subducting margin. This sample set augments previously studied xenolith suites in the Mojave Desert and Sierra Nevada, which linked the mantle lithosphere architecture and crustal structure of the western Cordillera. We examine six peridotite samples ranging from fertile lherzolites to harzburgite residues. Time‐corrected (ε_(Nd)) of 10.3–11.0 and ^(87)Sr/^(86)Sr of 0.702 are characteristic of underplated suboceanic mantle. Pyroxene exchange geothermometry shows equilibration at 950–1060 °C. Phase stability, Ca‐in‐olivine barometry, and 65‐ to 90‐mW/m^2 regional geotherms suggest entrainment at 45‐ to 75‐km depth. The samples were variably depleted by partial melting, and re‐enrichment of the hottest samples suggests deep melt‐rock interaction. We test the Crystal Knob temperature depth array against model geotherms matching potential sources for the mantle lithosphere beneath the Coast Ranges: (A) a shallow Mendocino slab window, (B) a young Monterey plate stalled slab, and (C) Farallon plate mantle nappes, underplated during the Cretaceous and reheated at depth by the Miocene slab window. Models B and C fit xenolith thermobarometry, but only model C fits the tectonic and geodynamic evolution of southern California. We conclude that the mantle lithosphere beneath the central California coast was emplaced after Cretaceous flat slab subduction and records a thermal signature of Neogene subduction of the Pacific‐Farallon ridge.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87799, title ="In situ observations of phase changes in shock compressed forsterite", author = "Newman, M. G. and Kraus, R. G.", journal = "Geophysical Research Letters", volume = "45", number = "16", pages = "8129-8135", month = "August", year = "2018", doi = "10.1029/2018GL077996", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180712-094708360", note = "© 2018 American Geophysical Union. \n\nManuscript received: 19 March 2018. Manuscript revised: 03 July 2018. Manuscript accepted: 05 July 2018. Accepted manuscript online: 11 July 2018. \n\nThis work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. MGN, MCA, and RGK acknowledge support under w under grant number 15-ERD-012. MCA, JVB, DCP, JL, and MAH acknowledge support under LLNL LDRD 16-ERD-010. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation - Earth Sciences (EAR-1634415) and Department of Energy- GeoSciences (DE-FG02-94ER14466). This publication is based upon work performed at the Dynamic Compression Sector, which is operated by Washington State University under the U.S. Department of Energy (DOE)/National Nuclear Security Administration award no. DE-NA0002442. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. JLM acknowledges support from NSF EAR-1161023. \n\nThe data used to generate this report is stored in the Caltech authors repository and can be accessed at http://resolver.caltech.edu/CaltechAUTHORS:20180520-171542198.\nThis document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes.", revision_no = "23", abstract = "Shockwave data on mineral‐forming compounds such as Mg2SiO4 are essential for understanding the interiors of Earth and other planets, but correct interpretation of these data depend on knowing the phase assemblage being probed at high pressure. Hence direct observations of the phase or phases making up the measured states along the forsterite Hugoniot are essential to assess whether kinetic factors inhibit the achievement of the expected equilibrium, phase‐separated assemblage. Previous shock recovery experiments on forsterite, which has orthorhombic space group Pbnm, show discrepant results as to whether forsterite undergoes segregation into its equilibrium phase assemblage of compositionally distinct structures upon shock compression. Here, we present the results of plate impact experiments on polycrystalline forsterite conducted at the Dynamic Compression Sector of the Advanced Photon Source. In situ x‐ray diffraction measurements were used to probe the crystal structure(s) in the shock state and to investigate potential decomposition into periclase and bridgmanite. In contrast to previous interpretations of the forsterite shock Hugoniot, we find that forsterite does not decompose, but instead reaches the forsterite III structure, which is a metastable structure of Mg_2SiO_4 with orthorhombic space group Cmc2_1.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88056, title ="Room-Temperature Pressure Synthesis of Layered Black Phosphorus–Graphene Composite for Sodium-Ion Battery Anodes", author = "Liu, Yihang and Liu, Qingzhou", journal = "ACS Nano", volume = "12", number = "8", pages = "8323-8329", month = "August", year = "2018", doi = "10.1021/acsnano.8b03615", issn = "1936-0851", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180720-103800132", note = "© 2018 American Chemical Society. \n\nReceived: May 14, 2018. Accepted: July 6, 2018. Publication Date (Web): July 20, 2018. \n\nWe acknowledge the collaboration of this research with King Abdul-Aziz City for Science and Technology (KACST) via The Center of Excellence for Nanotechnologies (CEGN). We acknowledge funding support from the University of Southern California. A portion of the images and data used in this article were acquired at The Center for Electron Microscopy and Microanalysis, University of Southern California. \n\nY.L. and Q.L. contributed equally to this work. \n\nThe authors declare no competing financial interest.", revision_no = "20", abstract = "Sodium-ion batteries offer an attractive option for grid-level energy storage due to the high natural abundance of sodium and low material cost of sodium compounds. Phosphorus (P) is a promising anode material for sodium-ion batteries, with a theoretical capacity of 2596 mAh/g. The red phosphorus (RP) form has worse electronic conductivity and lower initial Coulombic efficiency than black phosphorus (BP), but high material cost and limited production capacity have slowed the development of BP anodes. To address these challenges, we have developed a simple and scalable method to synthesize layered BP/graphene composite (BP/rGO) by pressurization at room temperature. A carbon-black-free and binder-free BP/rGO anode prepared with this method achieved specific charge capacities of 1460.1, 1401.2, 1377.6, 1339.7, 1277.8, 1123.78, and 720.8 mAh/g in a rate capability test at charge and discharge current densities of 0.1, 0.5, 1, 5, 10, 20, and 40 A/g, respectively. In a cycling performance test, after 500 deep cycles, the capacity of BP/rGO anodes stabilized at 1250 and 640 mAh/g at 1 and 40 A/g, respectively, which marks a significant performance improvement for sodium-ion battery anodes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86243, title ="Anomalous Pacific‐Antarctic Ridge volcanism precedes glacial Termination 2", author = "Lund, David C. and Seeley, Emily I.", journal = "Geochemistry, Geophysics, Geosystems", volume = "19", number = "8", pages = "2478-2491", month = "August", year = "2018", doi = "10.1029/2017GC007341", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180507-102834094", note = "© 2018 American Geophysical Union. \n\nReceived 14 NOV 2017; Accepted 18 APR 2018; Accepted article online 7 MAY 2018; Published online 16 AUG 2018. \n\nDCL and EIS were supported by NSF award OCE‐1558641 and the University of Connecticut. We are grateful to David Cady at UCONN for assistance with ICP‐MS analyses and Lora Wingate at the University of Michigan and Jean Lynch‐Stieglitz at Georgia Tech for assistance with stable isotope analyses. We are also indebted to the Oregon State University Core Repository for the curation of core OC170‐26‐159. The OSU Repository is supported by NSF award OCE‐1558679. MJL and PDA were supported by NSF awards OCE‐1558372 and EAR‐1551433. Thanks to Nathan Dalleska at Caltech for assistance with LA‐ICP‐MS analyses and to George Rossman for use of the FTIR lab. Electron probe work was carried out in the Caltech GPS Division analytical facility, which is supported in part by NSF Grants EAR‐0318518 and DMR‐0080065. Data presented in the manuscript will be available on the NOAA NGDC Paleoclimate Database and through IEDA PetDB.", revision_no = "22", abstract = "We present results from a well‐dated sediment core on the Pacific‐Antarctic Ridge (PAR) that document a ∼15 cm thick layer of basaltic ash shards that precedes the penultimate deglaciation (Termination 2). The glasses have MORB composition consistent with an axial source and their morphologies are typical of pyroclastic deposits created by submarine volcanism. The ash layer was deposited ∼7 km from the PAR axis, a distance that implies buoyant plumes lofted debris high into the water column with subsequent fallout to the core location. We infer plume rise height using grain settling velocities, the water depth at the core site, and deep ocean current speeds from ARGO floats. Rise heights of 1.5 km or less require unrealistically large current speeds to transport grains to the core site. Instead, the data are consistent with a plume rise height of at least 2 km, implying that T2 was an interval of anomalous volcanism along this segment of the PAR. The timing and duration of the ash deposit is consistent with glacial‐interglacial modulation of ridge magmatism. Volcaniclastic records from additional locations will be necessary to assess whether the PAR record is a rare find or it is representative of mid‐ocean ridge volcanism during glacial terminations.", } @experiment {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86485, title ="In situ observations of phase changes in shock compressed forsterite", author = "Newman, Matthew G. and Kraus, Richard", month = "July", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180520-171542198", note = "Plain Language Summary: \nModeling the interior structure of rocky planets requires us to understand the properties of planetary materials at the pressures and temperatures that are relevant to their interiors and formation processes. To measure the properties of the Earth's mantle at these conditions, researchers have traditionally performed hypervelocity impact experiments, launching a bullet at 10,000 mph into the sample of interest, which creates a shock wave that both heats and compresses the sample. Scientists then measure the temperature, pressure, and density of the samples using advanced diagnostics, from which they can learn how these materials would respond within the Earth or other large rocky planets. However, these impact experiments last one millionth of a second and we must ask ourselves, does an experiment that lasts one millionth of a second represent how a material responds on the tens of thousands of years timescale during mantle convection? Here we utilize a new diagnostic to measure the crystal structure of shock compressed forsterite at conditions similar to those deep within Earth's mantle. We find that forsterite does not reach the same state in a millionth of a second as it would in ten thousand years, instead it reaches a non‐equilibrium, or metastable structure.", revision_no = "18", abstract = "The high-pressure response of Mg2SiO4 forsterite is important for modeling chemical stratification in the mantle. Previous shock recovery experiments on forsterite show discrepant results as to whether forsterite undergoes segregation into its equilibrium phase assemblage of compositionally distinct structures upon shock compression. Here, we present the results of plate impact experiments on polycrystalline forsterite conducted at the Dynamic Compression Sector of the Advanced Photon Source. In situ x-ray diffraction measurements were used to probe the crystal structure(s) in the shock state and to investigate potential decomposition into periclase and bridgmanite. In contrast to previous interpretations of the forsterite shock Hugoniot, we find that forsterite does not decompose, but instead reaches the forsterite III structure, which is a metastable structure of Mg2SiO4. This work has important implications for the phase(s) that are present behind the shock front (kinetic versus equilibrium) for material systems that may phase segregate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87512, title ="On the relative timing of listwaenite formation and chromian spinel equilibration in serpentinites", author = "Gahlan, Hisham A. and Azer, Mokhles K.", journal = "American Mineralogist", volume = "103", number = "7", pages = "1087-1102", month = "July", year = "2018", doi = "10.2138/am-2018-6473", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180702-100734214", note = "© 2018 Mineralogical Society of America. \n\nManuscript received January 15, 2018; Manuscript accepted March 28, 2018. \n\nM.K.A.'s visit to the California Institute of Technology was supported by the U.S. Agency for International Development Cairo Initiative. P.D.A. acknowledges support from the U.S. National Science Foundation, award EAR-1551433. Special thanks are paid to King Saud University, Deanship of Scientific Research, Research Group No. RG-1436-036, for their suppprt.", revision_no = "12", abstract = "Ultramafic rocks exposed at the Earth's surface generally record multiple stages of evolution that may include melt extraction, serpentinization, carbonatization, and metamorphism. When quantitative thermometry based on mineral chemistry is applied to such rocks, it is often unclear what stage of their evolution is being observed. Here, in peridotites with extensive replacement of silicate minerals by carbonates (listwaenites), we present a case study that addresses the timing of carbonate formation relative to closure of exchange reactions among relict primary minerals.\nMassive and schistose serpentinized peridotites of Neoproterozoic age outcrop at Gabal Sirsir, South Eastern Desert, Egypt (northwestern corner of the Arabian-Nubian Shield or ANS). Petrography, bulk composition, and mineral chemistry are all consistent with a strongly depleted mantle harzburgite protolith for the serpentinites. Bulk compositions are low in Al_2O_3 and CaO and high in Mg# [molar Mg/(Mg+Fe) = 0.89–0.93]. Relict spinel has high Cr# [molar Cr/(Cr+Al)] and low Ti, while relict olivine has high Mg# and NiO contents. Based on compositions of coexisting relict olivine and chromian spinel, the protolith experienced 19 to 21% partial melt extraction. Such high degrees of partial melting indicate a supra-subduction zone environment, possibly a forearc setting.\nAlong thrust faults and shear zones, serpentinites are highly altered to form talc-carbonate rocks and weathering-resistant listwaenites that can be distinguished petrographically into Types I and II. The listwaenitization process took place through two metasomatic stages, associated first with formation of the oceanic crustal section and near-ridge processes (∼750–700 Ma) and subsequently during obduction associated with the collision of East and West Gondwana and escape tectonics (∼650–600 Ma). In the first stage, Mg# of chromian spinel in the serpentinites continuously changed due to subsolidus Mg–Fe^(2+) redistribution, while the Mg# of chromian spinel in the Type I listwaenites was frozen due to the absence of coexisting mafic silicates. During the second stage, the Type II listwaenites formed along shear zones accompanied by oxidation of relict chromian spinel to form ferritchromite and Cr-bearing magnetite in both serpentinites and listwaenites. The high Cr# of chromian spinel relics in both serpentinites and listwaenites preserves primary evidence of protolith melt extraction, but divalent cations are more easily mobilized at low temperature. Hence, relict chromian spinel in listwaenites shows significantly higher Mg# and lower MnO than that in serpentinite, suggesting that nearly complete alteration of ultramafic rocks to form listwaenite took place prior to re-equilibration between chromian spinel and the surrounding mafic minerals in serpentinites. Furthermore, the ferritchromite in the serpentinites has higher Mn content (1.1–2.1 wt%) than that in the listwaenites (0.6–0.9 wt%), indicating its formation after carbonatization since carbonate minerals are a favorable sink for Mn.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83508, title ="Geochemistry of the Serifos calc-alkaline granodiorite pluton, Greece: constraining the crust and mantle contributions to I-type granitoids", author = "Stouraiti, C. and Baziotis, I.", journal = "International Journal of Earth Sciences", volume = "107", number = "5", pages = "1657-1688", month = "July", year = "2018", doi = "10.1007/s00531-017-1565-7", issn = "1437-3254", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171128-104218804", note = "© 2017 Springer-Verlag GmbH Germany, part of Springer Nature. \n\nReceived: 22 July 2016; Accepted: 17 November 2017; First Online: 28 November 2017. \n\nThorough and extensive reviews by J. F. Moyen and R. Bolhar were welcomed. We appreciate the efficient editorial handling and constructive opinions on improving the manuscript by W. C. Dullo and the subject editor M. Elburg. We would like to thank Professor John Tarney (Leicester University) for his assistance in accomplishing research work at the University of Leicester. We greatly appreciate the invaluable assistance of Nick Marsh (XRF analysis) and Rob Wilson (electron microprobe analysis) at Leicester and of Andy Beard at Birkbeck, University of London. Field and analytical work was supported by the State Scholarship Foundation of Greece (IKY) and isotopic analyses by NERC (UK). We are particularly pleased to acknowledge Peter Greenwood and Barbara Barreiro (NERC Isotope Geoscience Laboratory). We would also like to acknowledge the authors of GCDkit software (V. Janoušek, G. Farrow and V. Erban) for providing free use of software to prepare geochemical plots. PDA acknowledges support from the US National Science Foundation, geoinformatics award EAR-1550934.", revision_no = "25", abstract = "The Late Miocene (11.6–9.5 Ma) granitoid intrusion on the island of Serifos (Western Cyclades, Aegean Sea) is composed of syn- to post-tectonic granodiorite with quartz monzodiorite enclaves, cut by dacitic and aplitic dikes. The granitoid, a typical I-type metaluminous calcic amphibole-bearing calc-alkaline pluton, intruded the Cycladic Blueschists during thinning of the Aegean plate. Combining field, textural, geochemical and new Sr–Nd–O isotope data presented in this paper, we postulate that the Serifos intrusion is a single-zoned pluton. The central facies has initial ^(87)Sr/^(86)Sr = 0.70906 to 0.7106, ε_(Nd)(t) = − 5.9 to −\u2009 7.5 and δ^(18)Ο_(qtz)\u2009=\u2009+\u200910 to +\u200910.6‰, whereas the marginal zone (or border facies) has higher initial ^(87)Sr/^(86)Sr = 0.711 to 0.7112, lower ε_(Nd)(t) = − \u20097.3 to − 8.3, and higher δ^(18)Ο_(qtz)\u2009=\u2009+\u200910.6 to +\u200911.9‰. The small range in initial Sr and Nd isotopic values throughout the pluton is paired with a remarkable uniformity in trace element patterns, despite a large range in silica contents (58.8 to 72 wt% SiO_2). Assimilation of a crustally derived partial melt into the mafic parental magma would progressively add incompatible trace elements and SiO2 to the evolving mafic starting liquid, but the opposite trend, of trace element depletion during magma evolution, is observed in the Serifos granodiorites. Thermodynamic modeling of whole-rock compositions during simple fractional crystallization (FC) or assimilation-fractional crystallization (AFC) processes of major rock-forming minerals—at a variety of pressure, oxidation state, and water activity conditions—fails to reproduce simultaneously the major element and trace element variations among the Serifos granitoids, implying a critical role for minor phases in controlling trace element fractionation. Both saturation of accessory phases such as allanite and titanite (at SiO_2\u2009≥\u200971 wt%)(to satisfy trace element constraints) and assimilation of partial melts from a metasedimentary component (to match isotopic data) must have accompanied fractional crystallization of the major phases.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87323, title ="Prehnite as an indicator mineral in the Wadi Nasb uralitized gabbro, South Sinai, Egypt", author = "Azer, Mokhles K. and Gahlan, Hisham A.", journal = "Journal of Asian Earth Sciences", volume = "160", pages = "107-117", month = "July", year = "2018", doi = "10.1016/j.jseaes.2018.04.011", issn = "1367-9120", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180622-104637599", note = "© 2018 Elsevier Ltd. \n\nReceived 2 November 2017, Revised 10 April 2018, Accepted 13 April 2018, Available online 14 April 2018.", revision_no = "6", abstract = "We report the first finding of prehnite in the southern Sinai peninsula, in a uralitized gabbro developed at the contact of the appinitic gabbro of the Wadi Nasb mafic intrusion (WNMI) with younger granitic intrusions. Subsolidus reactions with hydrothermal fluids caused the gabbro to gain Al_2O_3 and CaO while losing SiO_2, Fe_2O_3, TiO_2, P_2O_5, Ba, Nb, Zr and Y. Uralitization proceeded through two stages of alteration and mineral replacement. The early stage includes uralitization of pyroxene, formation of new biotite as aggregates of small flakes, transformation of primary amphiboles into actinolite and actinolitic hornblende, and saussuritization of plagioclase. The late stage of alteration is characterized by chloritization of mafic minerals. Apparent crystallization temperatures of the primary relics of pyroxene, hornblende and biotite range from 800–1000\u202f°C, 865–925\u202f°C, and ∼700\u202f°C, respectively, suggesting partial resetting of the biotite exchange thermometer. The early biotite-forming alteration occurred at moderate temperature (300–450\u202f°C), while the late chlorite-forming alteration occurred at low temperature (<300\u202f°C). The prehnite occurs in several forms: (1) fine grained aggregates mostly replacing feldspar and amphibole; (2) prehnite-biotite intergrowths; and (3) small veinlets and vug fillings. The formation of prehnite during the first stage is connected to alteration of pyroxene to secondary amphiboles and of plagioclase to albite, which released the CaO necessary for the development of prehnite. On the other hand, the late stage prehnite probably formed by open-system modification of the chemistry during late-stage fluid interaction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87466, title ="High pressure minerals in the Château-Renard (L6) ordinary chondrite: implications for collisions on its parent body", author = "Baziotis, Ioannis and Asimow, Paul D.", journal = "Scientific Reports", volume = "8", pages = "Art. No. 9851", month = "June", year = "2018", doi = "10.1038/s41598-018-28191-6", issn = "2045-2322", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180629-093135665", note = "© 2018 the Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. \n\nReceived 15 November 2017. Accepted 19 June 2018. Published 29 June 2018. \n\nThis research received support from SYNTHESYS (www.synthesys.info) [AT-TAF-4526], a European Union-funded Integrated Activities grant. JH was supported by the Caltech-JPL President and Director’s Fund. A.C. acknowledges funding received from the European Union’s Horizon 2020 research and innovation programme under grant agreement No -704696 RESOLVE. M.A. acknowledges funding by the UK Science and Technology Facilities Council (ST/L000776/1 & ST/P000657/1). F. Brandstaetter is kindly acknowledged for fruitful discussions during the stay of I.B. in Vienna. I.B. greatfully acknowledges the National Hellenic Research Foundation and E. Kamitsos for access to Raman facilities. \n\nAuthor Contributions: I.B., P.D.A., J.H., C.M., L.F. designed this research. L.F. curated and loaned to I.B. the meteorite sections. I.B., P.D.A., J.H., C.M., A.C., L.F., M.A. and D.T. observed and analysed the meteorite sections. I.B., with help from J.H. and P.D.A., constructed the thermal and transformation time modeling. All authors reviewed the manuscript. \n\nData Availability: The datasets generated during and/or analysed during the current study are included in this published article (and its Supplementary Information files) but also are available from the corresponding author on reasonable request. \n\nThe authors declare no competing interests.", revision_no = "22", abstract = "We report the first discoveries of high-pressure minerals in the historical L6 chondrite fall Château-Renard, based on co-located Raman spectroscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy and electron backscatter diffraction, electron microprobe analysis, and transmission electron microscopy (TEM) with selected-area electron diffraction. A single polished section contains a network of melt veins from ~40 to ~200\u2009μm wide, with no cross-cutting features requiring multiple vein generations. We find high-pressure minerals in veins greater than ~50\u2009μm wide, including assemblages of ringwoodite\u2009+\u2009wadsleyite, ringwoodite\u2009+\u2009wadsleyite\u2009+\u2009majorite-pyrope_(ss), and ahrensite\u2009+\u2009wadsleyite. In association with ahrensite\u2009+\u2009wadsleyite at both SEM and TEM scale, we find a sodic pyroxene whose Raman spectrum is indistinguishable from that of jadeite but whose composition and structure are those of omphacite. We discuss constraints on the impact record of this meteorite and the L-chondrites in general.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86308, title ="Secondary fluorescence effects in microbeam analysis and their impacts on geospeedometry and geothermometry", author = "Borisova, Anastassia Y. and Zagrtdenov, Nail R.", journal = "Chemical Geology", volume = "490", pages = "22-29", month = "June", year = "2018", doi = "10.1016/j.chemgeo.2018.05.010", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180509-104511407", note = "© 2018 Published by Elsevier B.V. \n\nReceived 21 November 2017, Revised 16 March 2018, Accepted 7 May 2018, Available online 9 May 2018. \n\nA.Y.B. thanks Nadezhda Sushchevskaya, Michel Pichavant, Didier Beziat, Jim Webster, and Sebastian Meffre for providing glass and mineral samples. A.Y.B. thanks Sebastian Meffre for providing unpublished data on reference zircons (e.g., Mud Tank zircon). This work has been supported by ISIFoR (ADERA 450710) grant to A.Y.B. in 2017–2018.", revision_no = "18", abstract = "Characteristic and bremsstrahlung X-ray emission during electron-specimen interactions in electron microprobe (EPMA) and scanning electron microscope (SEM) instruments causes secondary fluorescence X-ray effects from adjacent (boundary) phases. This is well-known, yet the impact of such effects in microbeam analysis of natural mineral-hosted inclusions and adjacent to mineral-mineral and mineral-glass boundaries are frequently neglected, especially in geospeedometry and geothermometry applications. To demonstrate the important influence of the secondary fluorescence effect on the measured concentration of elements and its consequences for geochemical applications, we consider the effect of mineral-mineral and mineral-glass boundaries in microanalysis of Cr, Zr and Ti both experimentally, using electron probe measurements on cold-pressed material couples, and computationally, using the software suite “CalcZAF/Standard” and its Graphical User Interface (GUI) for the semi-analytical model FANAL (Llovet et al., 2012). We demonstrate, for example, that apparent Cr contents of the order of ~3000 to 5000\u202fppm in chromite-hosted glass inclusions at 6\u202fμm from the inclusion boundary can be entirely due to secondary fluorescence in the Cr-rich host phase. Because the spatial gradient in secondary fluorescence-induced X-ray emission superficially resembles a diffusion profile, we emphasize the need to quantitatively correct for such effects in any geospeedometry application involving measurement of diffusion profiles adjacent to grain boundaries with large concentration contrasts. We also provide a scheme for estimating analytical errors related to the secondary fluorescence effect when applying geothermometers such as Ti-in-zircon, Ti-in-quartz (TitaniQ) and Zr-in-rutile. Temperature estimates based on trace Ti, Zr and Cr contents in minerals and glasses affected by secondary fluorescence in nearby phases (e.g., rutile, zircon and chromite) can be severely overestimated, in some cases by hundreds of degrees Celsius.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/85456, title ="Late Neoproterozoic adakitic lavas in the Arabian-Nubian shield, Sinai Peninsula, Egypt", author = "Abdelfadil, Khaled M. and Obeid, Mohamed A.", journal = "Journal of Asian Earth Sciences", volume = "158", pages = "301-323", month = "June", year = "2018", doi = "10.1016/j.jseaes.2018.02.018", issn = "1367-9120", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180327-110927212", note = "© 2018 Elsevier Ltd. \n\nReceived 15 November 2017, Revised 23 February 2018, Accepted 24 February 2018, Available online 2 March 2018.", revision_no = "7", abstract = "The Sahiya and Khashabi volcano-sedimentary successions are exposed near the southern tip of the Sinai Peninsula, the northernmost segment of the Arabian-Nubian Shield (ANS). These Neoproterozoic successions include a series of intermediate to acidic lavas and associated pyroclastic deposits. Field observations and geochemical data reveal two distinct eruptive phases. The lavas representing each phase are intercalated with volcaniclastic greywackes and siltstones. The first eruptive phase, well exposed at Wadi Sahiya, includes basaltic andesite, andesite and dacite with minor rhyolite. The rocks of this sequence are at most weakly deformed and slightly metamorphosed. The second eruptive phase, well exposed at Wadi Khashabi, includes only undeformed and unmetamorphosed dacite and rhyolite. The two volcano-sedimentary successions were separated and dismembered during intrusion of post-collisional calc-alkaline and alkaline granites. \n\nGeochemical compositions of the Sahiya and Khashabi volcanic rocks confirm the field data indicating discrete phases of magmatism, however all the compositions observed might plausibly be derived from a common source and be related to one another dominantly through fractional crystallization. The low and variable Mg# values (55–33) measured in the basaltic andesites and andesites preclude their equilibration with a mantle source. Rather, even the most primitive observed lavas are already the products of significant fractional crystallization, dominated by removal of amphibole and plagioclase. Continued fractionation eventually produced dacite and rhyolite marked by significant depletion in Y and HREE. The gradual appearance of negative Nb-Ta anomalies with increasing SiO_2 through both suites suggests at least some component of progressive crustal contamination.\nThe medium- to high-K calc-alkaline character of the Sahiya and Khashabi volcanics could be explained either by their formation at an active continental margin or by a two-stage model that appeals to re-melting of arc material in a post-collisional setting. The Wadi Sahiya basaltic andesite and andesite samples exhibit the defining chemical characteristics of adakites: high Sr (>700\u202fppm), low Y (<16\u202fppm), high Sr/Y (>20) and low Yb (<1.8\u202fppm). Although this signature can be associated with slab melting, here we show that it reflects partial melting of lithospheric mantle beneath thickened continental arc crust. The early eruptive phase, exposed at Sahiya, was erupted on an active continental margin, whereas the later Khashabi succession marks the transition to a post-collisional stage.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/85448, title ="The last subduction-related volcanism in the northern tip of the Arabian-Nubian Shield: A Neoproterozoic arc preceding the terminal collision of East and West Gondwana", author = "Maurice, Ayman E. and Bakhit, Bottros R.", journal = "Precambrian Research", volume = "310", pages = "256-277", month = "June", year = "2018", doi = "10.1016/j.precamres.2018.03.009", issn = "0301-9268", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180327-090036434", note = "© 2018 Elsevier B.V. \n\nReceived 29 October 2017, Revised 6 March 2018, Accepted 14 March 2018, Available online 15 March 2018. \n\nThe authors wish to thank Prof. Dr. Christoph Heinrich, ETH-Zürich, Switzerland, for laboratory facilities. Prof. Dr. Peter Ulmer, Dr. Eric Reusser and Lydia Zehnder are deeply acknowledged for the help in the geochemical and microprobe analyses conducted at ETH-Zürich. Comments by Prof. Moshe Eyal, Prof. Bernard Bonin and anonymous reviewers improved the present version of the manuscript. Dr. Kamal Ali (associate editor) and Prof. Guochun Zhao (editor) are acknowledged for editorial handling.", revision_no = "16", abstract = "The medium- to high-K calc-alkaline subduction-related Dokhan volcanic rocks of the Wadi Hamad area record two flare-up events during the history of a Neoproterozoic continental island arc, an early pulse dominated by andesite and a later pulse dominated by dacite. The trace element abundances and (La/Yb)_n ratios of the basalts, andesites and dacites all overlap, contrary to the expectations of a single fractional crystallization trend, suggesting the need for three distinct parental magmas for the three groups. The parental magmas of the basalts and andesites were generated by variable degrees of partial melting of subduction-metasomatized mantle, whereas that of the dacites requires mixing of mantle and crustal melts. The andesites and dacites both evolved mostly through fractionation of clinopyroxene and plagioclase, accompanied by apatite and Fe-Ti oxides in the more evolved dacitic rocks. Oscillatory and reverse zoning in clinopyroxene and plagioclase indicates that magma replenishment and mixing played a role in the genesis of the basalts and andesites. Depth-sensitive geochemical parameters show that the earlier andesites evolved at deeper levels in the arc crust compared with the later dacites, but not so deep as to stabilize garnet as a fractionating phase. Estimated values of the arc crust thickness indicate that the crust thickened from ∼35\u202fkm to ∼50\u202fkm from the time of basalt eruption to the time of andesite eruption, probably implying a high rate of crustal growth. The estimated arc crust thickness during the later subduction flare-up is slightly less than that of the earlier one despite ongoing magmatic addition, implying that arc crust delamination began before the production of the later dacites. The subduction-related geochemical characteristics of the Dokhan volcanic rocks suggest that the terminal collision between East and West Gondwana in the tip of the Nubian Shield occurred at ∼600\u202fMa.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100622, title ="Melts Under Extreme Conditions From Shock Experiments", author = "Asimow, Paul D.", pages = "387-418", month = "April", year = "2018", doi = "10.1016/b978-0-12-811301-1.00015-0", isbn = "978-0-12-811301-1", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200110-091509746", note = "© 2018 Elsevier Inc. \n\nAvailable online 13 April 2018.", revision_no = "5", abstract = "Shock compression methods form an important complement to static compression and computational approaches for probing the equation of state and thermodynamic properties of melts. This chapter summarizes shock compression, the theory by which laboratory shocks constrain liquid properties, and the standard experimental methods. It discusses the equations of state of several silicate liquid compositions and implications for microscopic structural mechanisms of liquid compression. From the available data, it examines the range of applicability and limitations of the linear mixing model for multicomponent liquid volumes and applies it to evaluate the relative buoyancy of melts and solids during lower-mantle magma ocean crystallization. Finally, the thermodynamic Grüneisen parameter is defined, its importance in shock wave research and in convecting systems explained, and its behavior according to shock experiments and molecular dynamics simulations discussed. Shock wave data on silicate liquids from several papers and recommended equation of state parameters for those liquids are compiled for convenient reference.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86034, title ="First-principles calculations of high-pressure iron-bearing monoclinic dolomite and single-cation carbonates with internally consistent Hubbard U", author = "Solomatova, Natalia V. and Asimow, Paul D.", journal = "Physics and Chemistry of Minerals", volume = "45", number = "3", pages = "293-302", month = "March", year = "2018", doi = "10.1007/s00269-017-0918-x", issn = "0342-1791", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180425-125649087", note = "© 2017 Springer-Verlag GmbH Germany. \n\nReceived: 16 May 2017; Accepted: 17 August 2017; Published online: 28 August 2017. \n\nWe thank K. Jarolimek, H. Hsu and H.J. Kulik for discussions. We are thankful to N. Near-Ansari for assistance with compiling relevant software and managing libraries on FRAM, the high-performance computing cluster at Caltech. This work is supported by the U.S. National Science Foundation through award EAR-1551433.", revision_no = "9", abstract = "It has been proposed that iron has a significant effect on the relative stability of carbonate phases at high pressures, possibly even stabilizing double-cation carbonates (e.g., dolomite) with respect to single-cation carbonates (e.g., magnesite, aragonite and siderite). X-ray diffraction experiments have shown that dolomite transforms at ~35 GPa to a high-pressure polymorph that is stable to decomposition; however, there has been disagreement on the structure of the high-pressure phase (Mao et al. in Geophys Res Lett 38, 2011. doi: 10.1029/2011GL049519; Merlini et al. in Proc Natl Acad Sci 109:13509–13514, 2012. doi: 10.1073/pnas.1201336109). Ab initio calculations interfaced with an evolutionary structure prediction algorithm demonstrated that a C2/c polymorph of pure CaMg(CO_3)_2 dolomite is more stable than previously reported structures (Solomatova and Asimow in Am Mineral 102:210–215, 2017, doi: 10.2138/am-2017-5830). In this study, we calculate the relative enthalpies up to 80 GPa for a set of carbonate phases including Fe-bearing solutions and endmembers, using the generalized gradient approximation and a Hubbard U parameter calculated through linear response theory to accurately characterize the electronic structure of Fe. When calculated with a constant U of 4 eV, the spin transition pressure of (Mg,Fe)CO_3 agrees well with experiments, whereas an internally consistent U overestimates the spin transition pressure by ~50 GPa. However, whether we use constant or internally consistent U values, a higher iron concentration increases the stability field of dolomite C2/c with respect to single-cation carbonate assemblages, but iron-free dolomite is not stable with respect to single-cation carbonates at any pressure. Thus, high-pressure polymorphs of Fe-bearing dolomite could in fact represent an important reservoir for carbon storage within oxidized sections of Earth’s mantle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/84363, title ="Thermodynamically complete equation of state of MgO from true radiative shock temperature measurements on samples preheated to 1850 K", author = "Fat'yanov, O. V. and Asimow, P. D.", journal = "Physical Review B", volume = "97", number = "2", pages = "Art. No. 024106", month = "January", year = "2018", doi = "10.1103/PhysRevB.97.024106", issn = "2469-9950", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180117-125209725", note = "© 2018 American Physical Society. \n\nReceived 8 August 2016; revised manuscript received 5 November 2017; published 16 January 2018. \n\nTechnical staff members of the Caltech Lindhurst Laboratory of Experimental Geophysics Michael Long, Epaprodito Gelle, and Russel Oliver are gratefully acknowledged for their expert assistance with all experiments. We thank our LLNL collaborators Samuel Weaver and Paul Benevento for sharing their extensive knowledge about successful operating of two-stage light-gas guns beyond 7 km/s and for providing the projectiles for our experiments 408–411. OVF thanks Prof. I. V. Lomonosov of IPCP RAS, Russia for giving access to the unpublished thermodynamic data for MgO predicted by the wide-range semiempirical EOS. This work was supported by the U.S. NSF, Award Nos. EAR-0810116 and EAR-1426526.", revision_no = "12", abstract = "Plate impact experiments in the 100–250 GPa pressure range were done on a ⟨100⟩ single-crystal MgO preheated before compression to 1850 K. Hot Mo(driver)-MgO targets were impacted with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 7.5 km/s. Radiative temperatures and shock velocities were measured with 3%–4% and 1%–2% uncertainty, respectively, by a six-channel pyrometer with 3-ns time resolution, over a 500–900-nm spectral range. MgO shock front reflectivity was determined in additional experiments at 220 and 248 GPa using ≈50/50 high-temperature sapphire beam splitters. Our measurements yield accurate experimental data on the mechanical, optical, and thermodynamic properties of B1 phase MgO from 102 GPa and 3900 K to 248 GPa and 9100 K, a region not sampled by previous studies. Reported Hugoniot data for MgO initially at ambient temperature, T=298 K, and the results of our current Hugoniot measurements on samples preheated to 1850 K were analyzed using the most general methods of least-squares fitting to constrain the Grüneisen model. This equation of state (EOS) was then used to construct maximum likelihood linear Hugoniots of MgO with initial temperatures from 298 to 2400 K. A parametrization of all EOS values and best-fit coefficients was done over the entire range of relevant particle velocities. Total uncertainties of all the EOS parameters and correlation coefficients for these uncertainties are also given. The predictive capabilities of our updated Mie-Grüneisen EOS were confirmed by (1) the good agreement between our Grüneisen data and five semiempirical γ(V) models derived from porous shock data only or from combined static and shock data sets, (2) the very good agreement between our 1-bar Grüneisen values and γ(T) at ambient pressure recalculated from reported experimental data on the adiabatic bulk modulus K_s(T), and (3) the good agreement of the brightness temperatures, corrected for shock reflectivity, with the corresponding values calculated using the current EOS or predicted by other groups via first-principles molecular dynamics simulations. Our experiments showed no evidence of MgO melting up to 250 GPa and 9100 K. The highest shock temperatures exceed the extrapolated melting curve of Zerr and Boehler by >3300 K and the upper limit for the melting boundary predictions of Aguado and Madden by >2600 K and those of Strachan et al. by >2100 K. We show that the potential for superheating in our shock experiments is negligible and therefore out data put a lower limit on the melting curve of B1 phase MgO in P−T space close to the set of consistent independent predictions by Sun et al., Liu et al., and de Koker and Stixrude.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83250, title ="Early Cretaceous high-Ti and low-Ti mafic magmatism in Southeastern Tibet: Insights into magmatic evolution of the Comei Large Igneous Province", author = "Wang, Yaying and Zeng, Lingsen", journal = "Lithos", volume = "296-299", pages = "396-411", month = "January", year = "2018", doi = "10.1016/j.lithos.2017.11.014", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171116-093457188", note = "© 2017 Elsevier B.V. \n\nReceived 5 May 2017, Accepted 12 November 2017, Available online 15 November 2017. \n\nThis study was supported by Special Scientific Research Fund of Public Welfare Profession of China (Grant No. 201511022), China Geological Survey Project (Grant No. 12120115027101), and National Science Foundation of China (Grant Nos. 41425010, 41503023). PDA's participation was supported by the US National Science Foundation, award EAR-1550934.", revision_no = "23", abstract = "The Dala diabase intrusion, at the southeastern margin of the Yardoi gneiss dome, is located within the outcrop area of the ~ 132 Ma Comei Large Igneous Province (LIP), the result of initial activity of the Kerguelen plume. We present new zircon U-Pb geochronology results to show that the Dala diabase was emplaced at ~ 132 Ma and geochemical data (whole-rock element and Sr-Nd isotope ratios, zircon Hf isotopes and Fe-Ti oxide mineral chemistry) to confirm that the Dala diabase intrusion is part of the Comei LIP. The Dala diabase can be divided into a high-Mg/low-Ti series and a low-Mg/high-Ti series. The high-Mg/low-Ti series represents more primitive mafic magma compositions that we demonstrate are parental to the low-Mg/high-Ti series. Fractionation of olivine and clinopyroxene, followed by plagioclase within the low-Mg series, lead to systematic changes in concentrations of mantle compatible elements (Cr, Co, Ni, and V), REEs, HFSEs, and major elements such as Ti and P. Some Dala samples from the low-Mg/high-Ti series contain large ilmenite clusters and show extreme enrichment of Ti with elevated Ti/Y ratios, likely due to settling and accumulation of ilmenite during the magma chamber evolution. However, most samples from throughout the Comei LIP follow the Ti-evolution trend of the typical liquid line of descent (LLD) of primary OIB compositions, showing strong evidence of control of Ti contents by differentiation processes. In many other localities, however, primitive magmas are absent and observed Ti contents of evolved magmas cannot be quantitatively related to source processes. Careful examination of the petrogenetic relationship between co-existing low-Ti and high-Ti mafic rocks is essential to using observed rock chemistry to infer source composition, location, and degree of melting.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83224, title ="Shock Synthesis of Decagonal Quasicrystals", author = "Oppenheim, J. and Ma, C.", journal = "Scientific Reports", volume = "7", pages = "Art. No. 15628", month = "November", year = "2017", doi = "10.1038/s41598-017-15229-4", issn = "2045-2322", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171115-104605836", note = "© 2017 The Authors. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. \n\nReceived: 18 August 2017; Accepted: 23 October 2017; Published online: 15 November 2017. \n\nJO was supported by Dr. George R. Rossman Summer Undergraduate Research Fellowship. The Caltech Lindhurst Laboratory of Experimental Geophysics and its staff members M. J. Burns and R. Oliver are supported by the National Science Foundation through award EAR-1426526. JH is supported by a grant from the Caltech/JPL President and Director’s Fund. We gratefully acknowledge support and infrastructure provided for this work by the Kavli Nanoscience Institute at Caltech. The Caltech GPS Division Analytical Facility is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065. \n\nAuthor Contributions: J.O. and P.D.A. conceived and executed the experiments. J.O., J.H., and C.M. analyzed the run products. J.O., J.H., and P.D.A. wrote the manuscript and all co-authors edited the manuscript. \n\nThe authors declare that they have no competing interests.", revision_no = "16", abstract = "The Khatyrka meteorite contains both icosahedral and decagonal quasicrystals. In our previous studies, icosahedral quasicrystals have been synthesized and recovered from shock experiments at the interface between CuAl_5 and stainless steel 304 alloys. In this study, we report a new shock recovery experiment aimed at synthesizing decagonal quasicrystals similar to decagonite, natural Al_(71)Ni_(24)Fe_5. Aluminum 2024 and permalloy 80 alloys were stacked together and shocked in a stainless steel 304 recovery chamber. Abundant decagonal quasicrystals of average composition Al_(73)Ni_(19)Fe_4Cu_2Mg_(0.6)Mo_(0.4)Mn_(0.3) with traces of Si and Cr were found along the recovered interface between the Al and permalloy. The experiment also synthesized AlNiFe alloy with the B2 (CsCl-type) structure and the metastable Al_9Ni_2 phase. We present chemical (scanning electron microscopy and electron microprobe) and structural (electron backscatter diffraction and transmission electron microscopy) characterization of the recovered phases and discuss the implications of this shock synthesis for the stability of quasicrystals during high-pressure shocks and for the interpretation of the phase assemblage found in Khatyrka.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83225, title ="Shock Synthesis of Five-component Icosahedral Quasicrystals", author = "Oppenheim, Julius and Ma, Chi", journal = "Scientific Reports", volume = "7", pages = "Art. No. 15629", month = "November", year = "2017", doi = "10.1038/s41598-017-15771-1", issn = "2045-2322", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171115-105645635", note = "© 2017 The Authors. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. \n\nReceived: 06 July 2017; Accepted: 01 November 2017; Published online: 15 November 2017. \n\nJO was supported by Dr. George R. Rossman Summer Undergraduate Research Fellowship. The Caltech Lindhurst Laboratory of Experimental Geophysics and its staff members M. J. Burns and R. Oliver are supported by the National Science Foundation through award EAR-1426526. JH is supported by a grant from the Caltech/JPL President and Director’s Fund. We gratefully acknowledge support and infrastructure provided for this work by the Kavli Nanoscience Institute at Caltech. The Caltech GPS Division Analytical Facility is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065. \n\nAuthor Contributions: J.O. and P.D.A. conceived and executed the experiments. J.O., J.H., and C.M. analyzed the run products. J.O., J.H., and P.D.A. wrote the manuscript and all co-authors edited the manuscript. \n\nThe authors declare that they have no competing interests.", revision_no = "12", abstract = "Five-component icosahedral quasicrystals with compositions in the range Al_(68–73)Fe_(11–16)Cu_(10–12)Cr_(1–4)Ni_(1–2) were recently recovered after shocking metallic CuAl_5 and (Mg_(0.75)Fe_(0.25))_2SiO_4 olivine in a stainless steel 304 chamber, intended to replicate a natural shock that affected the Khatyrka meteorite. The iron in those quasicrystals might have originated either from reduction of Fe^(2+) in olivine or from the stainless steel chamber. In this study, we clarify the shock synthesis mechanism of icosahedral quasicrystals through two new shock recovery experiments. When CuAl_5 and Fe^(2+)-bearing olivine were isolated in a Ta capsule, no quasicrystals were found. However, with only metallic starting materials, numerous micron-sized five-component icosahedral quasicrystals, average composition Al_(72)Cu_(12)Fe_(12)Cr_3Ni_1, were found at the interface between CuAl_5 and stainless steel, demonstrating nucleation of quasicrystals under shock without any redox reaction. We present detailed characterization of recovered quasicrystals and discuss possible mechanisms for generating sufficiently high temperatures to reach melting with relatively weak shocks. We discuss the implications of our five-component quasicrystal for the stability of quasicrystals, which have previously only been considered in alloy systems with four or fewer components. Even small amounts of additional metals expand the stability range of the icosahedral phase and facilitate routine syntheses without extraordinary precision in preparation of starting mixtures.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/80819, title ="Equation of state of liquid bismuth and its melting curve from ultrasonic investigation at high pressure", author = "Su, Chang and Liu, Yonggang", journal = "Physica B", volume = "524", pages = "154-162", month = "November", year = "2017", doi = "10.1016/j.physb.2017.08.049", issn = "0921-4526", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170825-160130142", note = "© 2017 Elsevier B.V. \n\nReceived 16 June 2017, Revised 12 August 2017, Accepted 18 August 2017, Available online 19 August 2017.", revision_no = "15", abstract = "To obtain the equation of state of liquid bismuth and its melting curve, ultrasonic velocity meapelisurements were performed in a multi-anvil apparatus. Using a series of thermodynamic relationships, we extract the volume of liquid bismuth as functions of pressure and temperature up to 973 K and 4.3 GPa. We also introduce a calculation process to build the thermal equations of state of each phase of solid bismuth based on their phase transition boundaries. Combining the thermodynamic parameters of liquid and solid bismuth, we employ the Gibbs equation and the Clausius-Clapeyron equation and finally derive the melting curve up to 8 GPa, which shows excellent consistency with most previous theoretical and experimental results. These results not only demonstrate the accuracy of our experimental and theoretical methods, but also demonstrate the feasibility of the thermodynamic method for obtaining unknown melting curves.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/82875, title ="The late Neoproterozoic Dahanib mafic-ultramafic intrusion, South eastern Desert, Egypt: Is it an Alaskan-type or a layered intrusion?", author = "Azer, Mokhles K. and Gahlan, Hisham A.", journal = "American Journal of Science", volume = "317", number = "8", pages = "901-940", month = "October", year = "2017", doi = "10.2475/08.2017.02 ", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171102-083956298", note = "© 2017 by American Journal of Science. \n\nWe are indebted to Geological Science Department, National Research Centre, Egypt for their support. Special thanks are paid to King Saud University, Deanship of Scientific Research, Research Group No. RG-1436-036 for their support. PDA is supported in part by the US National Science Foundation geoinformatics program, award number EAR-1550934. MKA's Post-doctoral mission to the Division of Geological and Planetary Sciences, California Institute of Technology (Caltech), USA, was supported by the Cairo Initiative of the US Agency for International Development. MKA is indebted to Professor George Rossman and Dr. Michael Baker, California Institute of Technology, for their kind assistance during his post-doctoral mission in Caltech. Special thanks to Dr. Chi Ma for his help with the microprobe analyses.", revision_no = "9", abstract = "In Egypt, mafic-ultramafic complexes have been classified into three major types: incomplete ophiolite sequences; Alaskan-type intrusions, concentrically-zoned bodies formed in a subduction arc environment; and layered intrusions, vertically-zoned bodies intruded in post-collisional tectonic environments and rift-related bodies associated with the opening of the Red Sea. We present new field work, geochemical data, mineral chemistry and interpretations for the late Neoproterozoic Dahanib mafic-ultramafic intrusion in the South Eastern Desert of Egypt (northernmost Arabian–Nubian Shield, ANS). The Dahanib intrusion shows no evidence of metamorphism or deformation, with excellent preservation of intrusive contacts, well-preserved textures and primary mineralogy. Field relations indicate that it is younger than the surrounding metamorphic rocks and syn-tectonic granitoids. The intrusion is composed of a basal suite of ultramafic rocks (dunite, lherzolite, wehrlite and pyroxenite) and an overlying suite of mafic rocks (olivine gabbronorite, gabbronorite and anorthosite). It displays evident layering of modal abundance, visible directly in outcrop, as well as cryptic layering discernible through changes in mineral compositions. The western and eastern lobes of the Dahanib intrusion occur in the form of a lopolith with readily correlated layers, especially in the upper mafic unit. The present-day dip of the layering decreases from the ultramafic units into the mafic sequence. Structural and compositional relations show that the ultramafic units are cumulates from a high-Mg tholeiitic parent magma emplaced at deep crustal levels and evolved via fractional crystallization rather than any kind of residual mantle sequence. Fo content of olivine and Mg# of pyroxenes display a systematic decrease from ultramafic to mafic rocks, well-correlated with whole-rock Mg#. Spinels in ultramafic samples vary from Cr-rich to Al-rich and have Mg# and Fe^(3+)# similar to spinels from typical stratiform complexes and clearly different from those found in ophiolitic and Alaskan-type complexes. Although the mafic and ultramafic units are clearly related and can be derived from common parent magma, they were not emplaced coevally; rather, they represent different pulses of magma. The Dahanib mafic–ultramafic intrusion does not display any features that convincingly identify it as a typical Alaskan-type body, particularly the lack of clinopyroxenite and hornblendite, rarity of primary hornblende, and the notable abundance of orthopyroxene and plagioclase in its rocks. Our results confirm that it is more akin to a layered mafic-ultramafic intrusion with a multistage evolution. It was emplaced into a stable post-orogenic cratonic setting, with a trace element signature indicating contamination of the mantle source by previous subduction events.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/79530, title ="Ultramafic lavas and high-Mg basaltic dykes from the Othris ophiolite complex, Greece", author = "Baziotis, Ioannis and Economou-Eliopoulos, Maria", journal = "Lithos", volume = "288-289", pages = "231-247", month = "September", year = "2017", doi = "10.1016/j.lithos.2017.07.015", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170728-085734946", note = "© 2017 Elsevier B.V. \n\nReceived 25 April 2017, Accepted 20 July 2017, Available online 28 July 2017. \n\nThis paper is dedicated to the memory of Professor George Paraskevopoulos, who discovered the ultramafic lavas in the Othris ophiolite complex, and passed away in 1997. \n\nMr. E. Michaelidis, University of Athens, is thanked for his assistance with the probe analyses. PDA was supported by the United States National Science Foundation through geoinformatics award EAR-1550934. We are grateful for the editorial handling by Andrew Kerr, and the fruitful comments made by Shoji Arai and an anonymous reviewer.", revision_no = "18", abstract = "We evaluate the petrography and geochemistry of an unusual suite of subduction-related Phanerozoic high-MgO rocks from the Othris ophiolite complex in Greece, some of which have previously been described as komatiitic lavas. In particular, we study ultramafic, olivine-phyric lavas from the Agrilia area and high-Mg basaltic dykes from the Pournari area. We seek to define primary magmatic MgO contents and initial liquidus temperatures as well as the differentiation sequence and cooling rates experienced by the lavas and dykes. One of our goals is to relate the Othris case to known komatiite and boninite occurrences and to address whether Othris documents an important new constraint on the temporal evolution of ambient mantle temperature, plume-related magmatism, and subduction of oceanic lithosphere. We conclude that, despite whole-rock MgO contents of 31–33 wt%, the olivine-phyric lavas at Agrilia had an upper limit liquid MgO content of 17 wt% and are therefore picrites, not komatiites. The Agrilia lavas contain the unusual Ti-rich pyroxenoid rhönite; we discuss the significance of this occurrence. In the case of the Pournari high-Mg dykes, the distinctive dendritic or plumose clinopyroxene texture, though it resembles in some ways the classic spinifex texture of komatiites, is simply evidence of rapid cooling at the dyke margin and not evidence of extraordinarily high liquidus temperatures. We correlate the dendritic texture with disequilibrium mineral chemistry in clinopyroxene to constrain the cooling rate of the dyke margins.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86191, title ="Geochemistry and petrogenesis of post-collisional alkaline and peralkaline granites of the Arabian-Nubian Shield: a case study from the southern tip of Sinai Peninsula, Egypt", author = "Khalil, A. E. S. and Obeid, M. A.", journal = "International Geology Review", volume = "60", number = "8", pages = "998-1018", month = "August", year = "2017", doi = "10.1080/00206814.2017.1364672", issn = "0020-6814", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180502-104518099", note = "© 2017 Taylor & Francis. \n\nReceived 23 Feb 2017, Accepted 03 Aug 2017, Published online: 21 Aug 2017. \n\nDr Azer has fellowship from the Cairo Initiative grant of the United States Agency for International Development to visit the Division of Geological & Planetary Sciences (GPS), California Institute of Technology, USA. PDA’s participation in the work is supported by the US National Science Foundation geoinformatics program under award EAR-1550934.", revision_no = "9", abstract = "The southern Sinai Peninsula, underlain by the northernmost extension of the Arabian-Nubian Shield, exposes post-collisional calc-alkaline and alkaline granites that represent the youngest phase of late Neoproterozoic igneous activity. We report a petrographic, mineralogical and geochemical investigation of post-collisional plutons of alkaline and, in some cases, peralkaline granite. These granites intrude metamorphosed country rocks as well as syn- and post-collisional calc-alkaline granitoids. The alkaline and peralkaline granites of the southern tip of Sinai divide into three subgroups: syenogranite, alkali feldspar granite and riebeckite granite. The rocks of these subgroups essentially consist of alkali feldspar and quartz with variable amounts of plagioclase and mafic minerals. The syenogranite and alkali feldspar granite contain small amounts of calcic amphibole and biotite, often less than 3%, while the riebeckite granite is distinguished by sodic amphibole (5–10%). These plutons have geochemical signatures typical of post-collisional A-type granites and were most likely emplaced during a transition between orogenic and anorogenic settings. The parental mafic magma may be linked to lithospheric delamination and upwelling of asthenospheric mantle material. Differentiation of the underplated basaltic magma with contributions from the juvenile crust eventually yielded the post-collisional alkaline granites. Petrogenetic modelling of the studied granitic suite shows that pure fractional crystallization cannot quantitatively explain chemical variations with the observed suite, with both major oxides and several trace elements displaying trends opposite to those required by the equilibrium phase assemblage. Instead, we show that compositional variation from syenogranite through alkali feldspar granite to riebeckite granite is dominated by mixing between a low-SiO_2 liquid as primitive or more primitive than the lowest-SiO_2 syenogranite and an evolved, high-SiO_2 liquid that might be a high-degree partial melt of lower crust.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86036, title ="An example of post-collisional appinitic magmatism with an arc-like signature: the Wadi Nasb mafic intrusion, north Arabian–Nubian Shield, south Sinai, Egypt", author = "Gahlan, Hisham A. and Obeid, Mohamed A.", journal = "International Geology Review", volume = "60", number = "7", pages = "865-888", month = "August", year = "2017", doi = "10.1080/00206814.2017.1360804", issn = "0020-6814", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180425-130655654", note = "© 2018 Taylor & Francis. \n\nReceived 20 May 2017, Accepted 25 Jul 2017, Published online: 14 Aug 2017.", revision_no = "9", abstract = "We present new data for the Neoproterozoic mafic intrusion exposed in Wadi Nasb, south Sinai, Egypt (northernmost Arabian–Nubian Shield; ANS). The Nasb mafic intrusion (NMI) intrudes metasediments, Rutig volcanics, and diorite/granodiorite, and is intruded in turn by younger monzogranite and quartz-monzonite. Available geochronological data for the country rocks of the NMI provide a tight constraint on its age, between 619 and 610 Ma, during the hiatus between the lower and upper Rutig volcanics. The NMI is neither deformed nor metamorphosed, indicating post-collisional emplacement, and uralitization by late-magmatic and sub-solidus alteration is restricted to the margins of the intrusion. A quantitative fractionation model indicates a fractionating assemblage of 61% primary amphibole, 10% clinopyroxene, 28% plagioclase, 1% biotite, 0.4% apatite, and 0.15% Fe-Ti oxide. Contrary to the recent studies, we find that the nearby diorite of Gebel Sheikh El-Arab is not co-genetic with the appinitic gabbro of the NMI. Although there are volcanic xenoliths in the NMI, we find no chemical evidence requiring contamination by continental crust. A subduction-related signature in a post-orogenic intrusion requires the inheritance of geochemical tendencies from a previous subduction phase. Given that the fine-grained gabbro of the NMI is consistent with a near-primary mantle melt, we attribute this inheritance to persistence and later melting of the slab-modified mantle domains, as opposed to partial melting and assimilation of the juvenile continental crust. The fine-grained gabbro composition indicates derivation at temperature and pressure conditions similar to the sources of mid-ocean ridge basalts: mantle potential temperature near 1350°C and extent of melting about 7%. Such temperatures, neither so high as to require a plume nor so low as to be consistent with small degrees of melting of a volatile-rich source, are most consistent with a lithospheric delamination scenario, allowing the upwelling of fertile, subduction-modified asthenosphere to depths ≤50 km.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77778, title ="Highly CO_2-supersaturated melts in the Pannonian lithospheric mantle – A transient carbon reservoir?", author = "Créon, Laura and Rouchon, Virgile", journal = "Lithos", volume = "286-287", pages = "519-533", month = "August", year = "2017", doi = "10.1016/j.lithos.2016.12.009", issn = "0024-4937", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170525-161258053", note = "© 2017 Elsevier B.V. \n\nReceived 22 August 2016, Accepted 8 December 2016, Available online 16 December 2016. \n\nThis project was funded by IFP Energies nouvelles. The European Synchrotron Research Facility of Grenoble, the ID19 beamline team and more specifically Paul Tafforeau are thanked for their financial and technical support. The National NanoSIMS facility at the MNHN was established by funds from the CNRS, Région Ile de France, Ministère délégué à l'Enseignement supérieur et à la Recherche, and the MNHN. PDA and PMA acknowledge support by the US NSF geoinformatics program, award 1550934. We are grateful to Marie-Claude Lynch and Herman Ravelojaona for their precious assistance with X-ray tomography and sample preparations. The paper benefitted from thoughtful reviews by Andrea Giuliani and an anonymous reviewer.", revision_no = "18", abstract = "Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO_2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO_2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO_2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO_2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0–0.25 wt.% CO_2), whereas the H_2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9–6.3 wt.% H_2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO_2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions determined by Raman spectroscopy and microthermometry (0.1–1.1 GPa). The CO_2/silicate melt mass ratios in the metasomatic agent that percolated through the lithospheric mantle below the Pannonian Basin are estimated to be between 9.0 and 25.4 wt.%, values consistent with metasomatism either by (1) silicate melts already supersaturated in CO_2 before reaching lithospheric depths or (2) carbonatite melts that interacted with mantle peridotite to generate carbonated silicic melts. Taking the geodynamical context of the Pannonian Basin and our calculations of the CO_2/silicate melt mass ratios in the metasomatic agent into account, we suggest that slab-derived melts initially containing up to 25 wt.% of CO_2 migrated into the lithospheric mantle and exsolved CO_2–rich fluid that became trapped in secondary fluid inclusions upon fracturing of the peridotite mineral matrix. We propose a first-order estimate of 2000 ppm as the minimal bulk CO_2 concentration in the lithospheric mantle below the Pannonian Basin. This transient carbon reservoir is believed to be degassed through the Pannonian Basin due to volcanism and tectonic events, mostly focused along the lithospheric-scale regional Mid-Hungarian shear Zone.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77756, title ="An Andean-type arc system in Rodinia constrained by the Neoproterozoic Shimian ophiolite in South China", author = "Zhao, Jun-Hong and Asimow, Paul D.", journal = "Precambrian Research", volume = "296", pages = "93-111", month = "July", year = "2017", doi = "10.1016/j.precamres.2017.04.017", issn = "0301-9268", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170525-111145489", note = "© 2017 Elsevier B.V. \n\nReceived 19 December 2016, Revised 31 March 2017, Accepted 7 April 2017, Available online 10 April 2017. \n\nThis work was substantially supported by the National Nature Science Foundation of China (41373016 and 41573020) and the Young Thousand Talent Program (32110-32020002). PDA was supported in part by the US National Science Foundation through award EAR-1550934. Reviews by Prof. Manoj K. Pandit and the anonymous referee are gratefully acknowledged.", revision_no = "10", abstract = "The configuration of the supercontinent Rodinia has long been a matter of debate; the key controversy is the position of South China in Rodinia. We report an incomplete Neoproterozoic ophiolite sequence, including gabbros and serpentinized peridotites intruded by mafic dikes, near Shimian (Sichuan Province), along the western margin of the Yangtze Block in South China. Serpentinized peridotites have very low REE (0.14–1.16 ppm) and trace element concentrations, and are interpreted as parts of a depleted mantle sequence. Chromites from the serpentinized peridotites have low TiO_2 (<0.3 wt%) and Fe_2O_3 (<7.6 wt%), and moderate Cr/(Cr + Al) (0.48–0.67) and Mg/(Mg + Fe^(2+)) (0.42–0.67) ratios and are clearly indicative of strong depletion of the host peridotites, similar to those of supra-subduction zone (SSZ). Mafic dikes and gabbros contain zircon grains with similar U-Pb ages of ∼800 Ma, and are chemically akin to MORB-like tholeiitic basalts and boninite-series volcanic rocks reported in other SSZ ophiolites and in the Izu-Bonin-Mariana arc system. Therefore, the serpentinized peridotite, mafic dikes and gabbros together appear to form a SSZ-type ophiolite assemblage preserving the accretion of oceanic lithosphere to the western Yangtze Block. The age and location of the Shimian ophiolite rule out the possibility that South China was located in the centre of Rodinia. Instead, the Neoproterozoic arc-affinity igneous rocks at the western margin of the Yangtze Block are well correlated with those in Greater India and Madagascar. These three blocks thus together formed a giant Andean-type arc system along the NW margin of Rodinia that existed for more than 100 Mys.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/78665, title ="Phosphorus zoning as a recorder of crystal growth kinetics: application to second-generation olivine in mantle xenoliths from the Cima Volcanic Field", author = "Baziotis, I. and Asimow, P. D.", journal = "Contributions to Mineralogy and Petrology", volume = "172", number = "7", pages = "Art. No. 58", month = "July", year = "2017", doi = "10.1007/s00410-017-1376-7", issn = "0010-7999", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170628-141227028", note = "© 2017 Springer-Verlag GmbH Germany. \n\nReceived: 28 February 2017. Accepted: 29 May 2017. \n\nCommunicated by Othmar Müntener. \n\nThe studied specimens were loaned for this research by the Division of Petrology and Volcanology, Department of Mineral Sciences, Smithsonian Institution. We are grateful for the editorial handling by Mark Ghiorso, and the fruitful comments made by Benoit Welsch and an anonymous reviewer. I.B. funds for this research project implemented within the framework of the Action «Supporting Postdoctoral Researchers» of the Operational Program “Education and Lifelong Learning” (Action’s Beneficiary: General Secretariat for Research and Technology), and is co-financed by the European Social Fund (ESF) and the Greek State, and the IKYDA project with title: “Petrology and Geochemistry of composite mantle xenoliths”. PDA is supported by the US NSF through geoinformatics award EAR-1550934. Quadlab is funded by a Grant to MS from the Villum Foundation. JWB was supported by NASA Grant NNX13AG40G. DP acknowledges the European Research Council (ERC) for the Consolidator Grant ERC-2013-CoG No. 612776–CHRONOS. We are really grateful for thoughtful comments by Prof. Ed Stolper and his contributions throughout the gestation of this manuscript. An earlier version of this manuscript was reviewed by G. Wörner, Cliff Shaw, Benoit Welsch, and an anonymous reviewer.", revision_no = "30", abstract = "Composite mantle xenoliths from the Cima Volcanic Field (CA, USA) contain glassy veins that cross-cut lithologic layering and preserve evidence of lithospheric melt infiltration events. Compositions and textures of minerals and glasses from these veins have the potential to place constraints on the rates and extents of reaction during infiltration. We studied glass-bearing regions of two previously undescribed composite xenoliths, including optical petrography and chemical analysis for major and trace elements by electron probe microanalysis and laser-ablation inductively coupled plasma mass spectrometry. The petrogenetic history of each vein involves melt intrusion, cooling accompanied by both wall-rock reaction and crystallization, quench of melt to a glass, and possibly later modifications. Exotic secondary olivine crystals in the veins display concentric phosphorus (P)-rich zoning, P-rich glass inclusions, and zoning of rapidly diffusing elements (e.g., Li) that we interpret as records of rapid disequilibrium events and cooling rates on the order of 10 °C/h. Nevertheless, thermodynamic modeling of the diversity of glass compositions recorded in one of the samples demonstrates extensive reaction with Mg-rich olivine from the matrix before final quench. Our results serve as a case study of methods for interpreting the rates and processes of lithospheric melt-rock reactions in many continental and oceanic environments.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/74755, title ="A measure of mantle melting", author = "Asimow, Paul D.", journal = "Science", volume = "355", number = "6328", pages = "908-909", month = "March", year = "2017", doi = "10.1126/science.aam7807", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170306-074710346", note = "© 2017 American Association for the Advancement of Science.", revision_no = "10", abstract = "Earth's interior is hot, as is evident from geothermal heat flow, the existence of volcanoes, and the mobility of tectonic plates. But just how hot is it? The temperature increases rapidly with depth through the rigid lithosphere in order to conduct geothermal heat flow, but this cannot continue downward indefinitely without reaching the melting point of rocks. Yet there is no global molten layer below the lithosphere. The propagation of shear waves through the upper mantle shows that it is solid. Rather, the conductive heat flow gives way at some depth to the transport of heat by solid-state convection in the ductile asthenosphere. Convecting systems evolve to an adiabatic temperature profile that can be characterized by a single reference, the “potential temperature.” Determining the average and range of variability of the potential temperature of the mantle below the lithosphere allows geoscientists to link observations of phenomena such as postglacial rebound and seismic wave speeds, through laboratory data on viscous and elastic properties, to the composition of Earth. On page 942 of this issue, Sarafian et al. (1) report new experimental observations of the melting of mantle rocks with the appropriate amount of water and infer a higher value of the potential temperature than previous estimates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/75382, title ="Equation of state of Mo from shock compression experiments on preheated samples", author = "Fat'yanov, O. V. and Asimow, P. D.", journal = "Journal of Applied Physics", volume = "121", number = "11", pages = "Art. No. 115904", month = "March", year = "2017", doi = "10.1063/1.4978607", issn = "0021-8979", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170324-093720621", note = "© 2017 AIP Publishing. \n\nReceived 22 November 2016; accepted 2 March 2017; published online 21 March 2017. \n\nO.V.F. thanks Professor I. V. Lomonosov of IPCP RAS, Russia, for numerous stimulating discussions on the subject and Professor S. Brandt of Siegen University, Germany, for his clarification on the origin of the most accurate least-squares fitting method reported. This work was supported by the U.S. NSF, Award Nos. EAR-0810116 and EAR-1426526.", revision_no = "14", abstract = "We present a reanalysis of reported Hugoniot data for Mo, including both experiments shocked from ambient temperature (T) and those preheated to 1673\u2009K, using the most general methods of least-squares fitting to constrain the Grüneisen model. This updated Mie-Grüneisen equation of state (EOS) is used to construct a family of maximum likelihood Hugoniots of Mo from initial temperatures of 298 to 2350\u2009K and a parameterization valid over this range. We adopted a single linear function at each initial temperature over the entire range of particle velocities considered. Total uncertainties of all the EOS parameters and correlation coefficients for these uncertainties are given. The improved predictive capabilities of our EOS for Mo are confirmed by (1) better agreement between calculated bulk sound speeds and published measurements along the principal Hugoniot, (2) good agreement between our Grüneisen data and three reported high-pressure γ(V) functions obtained from shock-compression of porous samples, and (3) very good agreement between our 1\u2009bar Grüneisen values and γ(T) at ambient pressure recalculated from reported experimental data on the adiabatic bulk modulus K_s(T). Our analysis shows that an EOS constructed from shock compression data allows a much more accurate prediction of γ(T) values at 1\u2009bar than those based on static compression measurements or first-principles calculations. Published calibrations of the Mie-Grüneisen EOS for Mo using static compression measurements only do not reproduce even low-pressure asymptotic values of γ(T) at 1\u2009bar, where the most accurate experimental data are available.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/73476, title ="Ab initio study of the structure and stability of CaMg(CO_3)_2 at high pressure", author = "Solomatova, Natalia V. and Asimow, Paul D.", journal = "American Mineralogist", volume = "102", number = "1", pages = "210-215", month = "January", year = "2017", doi = "10.2138/am-2017-5830", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170112-124637100", note = "© 2017 Mineralogical Society of America. \n\nManuscript received April 26, 2016; Manuscript accepted August 24, 2016; Manuscript handled by Martin Kunz. \n\nWe thank E.A. Schauble, A. Kavner, M. Merlini, G.F. Finkelstein, A.R. Oganov, and O. Hellman for valuable discussions and insights. We are thankful to N. Near-Ansari for assistance with technical aspects using FRAM, the high-performance computing cluster at Caltech. This work is supported by the U.S. National Science Foundation through award EAR-1551433.", revision_no = "12", abstract = "Dolomite is one of the major mineral forms in which carbon is subducted into the Earth’s mantle. End-member CaMg(CO_3)_2 dolomite typically breaks down upon compression into two carbonates at 5–6 GPa in the temperature range of 800–1200 K (Shirasaka et al. 2002). However, high-pressure X-ray diffraction experiments have shown that dense high-pressure polymorphs of dolomite may be favored over single-cation carbonates (Santillán et al. 2003; Mao et al. 2011; Merlini et al. 2012). Here we compare calculated dolomite structures to experimentally observed phases. Using density functional theory interfaced with a genetic algorithm that predicts crystal structures (USPEX), a monoclinic phase with space group C2/c was found to have lower energy at pressures above 15 GPa than all previously reported dolomite structures. It is possible that this phase is not observed experimentally due to a large activation energy of transition from dolomite I, resulting in the observed second-order phase transition to a metastable dolomite II. Due to the complex energy landscape for candidate high-pressure dolomite structures, several structurally unique metastable polymorphs exist. We calculate the equation of state of a set of lowest-energy dolomite polymorphs with space groups P1, P2/c, and C2/c up to 80 GPa. Our results demonstrate a need for calculations and experiments on Fe-Mn bearing high-pressure carbonate phases to extend our understanding of Earth’s deep carbon cycle and test whether high-pressure polymorphs of double-cation carbonates represent the main reservoir for carbon storage within downwelling regions of Earth’s mantle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/72103, title ="Contrasting geochemical signatures of fluid-absent versus fluid-fluxed melting of muscovite in metasedimentary sources: The Himalayan leucogranites", author = "Gao, Li-E. and Zeng, Lingsen", journal = "Geology", volume = "45", number = "1", pages = "39-42", month = "January", year = "2017", doi = "10.1130/G38336.1", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161117-090300833", note = "© 2016 Geological Society of America. \n\nManuscript received 8 July 2016; Revised manuscript received 8 October 2016; Manuscript accepted 17 October 2016; First Published on November 03, 2016. \n\nThis study was supported by National Key Research and Development Project of China (grant 2016YFC0600304), National Science Foundation of China (grants 41425010, 41503023, and 41273034), and China Geological Survey (grants 12120114022701 and 12120115027101). Participation by Asimow was supported by the U.S. National Science Foundation through Geoinformatics award EAR-1226270. Thanks go to Editor James Spotila for carefully handling this manuscript, and to Nigel Harris, Michael Brown, Calvin Miller, Antonio Acosta-Vigil, and one anonymous reviewer for their constructive comments.", revision_no = "21", abstract = "Most of the Himalayan Cenozoic leucogranites are products of partial melting of metapelite sources. In the Malashan-Gyirong area (southern Tibet), the geochemical compositions of leucogranites define two groups with distinct whole-rock major elements, large ion lithophile elements, rare earth elements, high field strength elements, and Sr and Hf isotope ratios. Based on published experimental results that define generalized melting reactions of metapelitic sources, we infer that these leucogranites are the products of two different types of crustal anatexis: fluid-fluxed melting and fluid-absent melting of muscovite in metasedimentary sources. As compared to the leucogranites derived from fluid-absent melting, those from fluid-fluxed melting have relatively higher Ca, Sr, Ba, Zr, Hf, Th, and light rare earth element concentrations, and Zr/Hf, Eu/Eu*, and Nd/Nd*, but lower Rb, Nb, Ta, and U concentrations, Rb/Sr and ^(87)Sr/^(86)Sr ratios, and ε_(Hf)(t). The geochemical differences can be explained by melting behaviors of major (muscovite, feldspar) and accessory minerals (zircon and monazite) during different modes of crustal anatexis. The systematic elemental and isotopic signatures of different types of crustal anatexis and, in particular, the coupling of major and trace elements that results from common influences on rock-forming and accessory mineral behaviors provide tools with which to refine our understanding of the nature of crustal anatexis.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/70996, title ="Mineral chemistry of the Tissint meteorite: Indications of two-stage crystallization in a closed system", author = "Liu, Yang and Baziotis, Ioannis P.", journal = "Meteoritics and Planetary Science", volume = "51", number = "12", pages = "2293-2315", month = "December", year = "2016", doi = "10.1111/maps.12726", issn = "1086-9379", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161011-120243183", note = "© 2016 Meteoritical Society. \n\nReceived 04 February 2016; revision accepted 10 July 2016. Version of Record online: 5 Oct 2016. \n\nWe thank Allan Patchen and Luca Fedele for their assistance with data collection. Comments from the AE (C. Goodrich), T. Usui, C. Herd, and M. McCanta on earlier versions of the manuscript have significantly improved the presentation and are greatly appreciated. We acknowledge partial support by NASA Cosmochemistry grants NNX11AG58G to LAT, NNN13D465T to YL, NSF Grant EAR-1226270 to PDA, and NSF Grant EAR-1019770 to RJB. YL is supported by the Jet Propulsion Laboratory, which is managed by the California Institute of Technology under a contract with NASA.", revision_no = "20", abstract = "The Tissint meteorite is a geochemically depleted, olivine-phyric shergottite. Olivine megacrysts contain 300–600 μm cores with uniform Mg# (~80 ± 1) followed by concentric zones of Fe-enrichment toward the rims. We applied a number of tests to distinguish the relationship of these megacrysts to the host rock. Major and trace element compositions of the Mg-rich core in olivine are in equilibrium with the bulk rock, within uncertainty, and rare earth element abundances of melt inclusions in Mg-rich olivines reported in the literature are similar to those of the bulk rock. Moreover, the P Kα intensity maps of two large olivine grains show no resorption between the uniform core and the rim. Taken together, these lines of evidence suggest the olivine megacrysts are phenocrysts. Among depleted olivine-phyric shergottites, Tissint is the first one that acts mostly as a closed system with olivine megacrysts being the phenocrysts. The texture and mineral chemistry of Tissint indicate a crystallization sequence of: olivine (Mg# 80 ± 1) → olivine (Mg# 76) + chromite → olivine (Mg# 74) + Ti-chromite → olivine (Mg# 74–63) + pyroxene (Mg# 76–65) + Cr-ulvöspinel → olivine (Mg# 63–35) + pyroxene (Mg# 65–60) + plagioclase, followed by late-stage ilmenite and phosphate. The crystallization of the Tissint meteorite likely occurred in two stages: uniform olivine cores likely crystallized under equilibrium conditions; and a fractional crystallization sequence that formed the rest of the rock. The two-stage crystallization without crystal settling is simulated using MELTS and the Tissint bulk composition, and can broadly reproduce the crystallization sequence and mineral chemistry measured in the Tissint samples. The transition between equilibrium and fractional crystallization is associated with a dramatic increase in cooling rate and might have been driven by an acceleration in the ascent rate or by encounter with a steep thermal gradient in the Martian crust.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/79143, title ="Partial Melting", author = "Asimow, Paul D.", pages = "1-6", month = "November", year = "2016", doi = "10.1007/978-3-319-39193-9_218-1", issn = "1388-4360", isbn = "978-3-319-39193-9", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170718-085240038", note = "© 2016 Springer International Publishing AG.", revision_no = "7", abstract = "Partial melting is the transformation of some fraction of the mass of a solid rock into a liquid as a result of decompression, heat input, or addition of a flux. The resulting liquid is called magma and becomes lava if it erupts from a volcano. The understanding that partial, rather than complete, melting is the norm in natural systems is essential to appreciating the geochemical importance of melting in the Earth and planets. During partial melting, the liquid differs from the source rock and from coexisting residual minerals in composition and in physical properties such as density and viscosity.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/71527, title ="Genesis and petrology of Late Neoproterozoic pegmatites and aplites associated with the Taba metamorphic complex in southern Sinai, Egypt", author = "Abdelfadil, K. M. and Asimow, P. D.", journal = "Geologica Acta", volume = "14", number = "3", pages = "219-235", month = "September", year = "2016", doi = "10.1344/GeologicaActa2016.14.3.2", issn = "1695-6133", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161027-074715973", note = "© 2016 University of Barcelona. This work is licensed under a Creative Commons Attribution-ShareAlike License. \n\nManuscript received January 2016; revision accepted March 2016; published Online June 2016. \n\nWe are indebted to King Saud University, Deanship of Scientific Research, Research Group Nº RG-1436-036, for their support. MKA’s visit to the Division of Geological & Planetary Sciences, California Institute of Technology, USA, was supported by the Cairo Initiative of the US Agency for International Development. Special thanks to Prof. George Rossman and Michael Baker for use of sample preparation facilities at Caltech. Also, the authors would like to thank Chi Ma for his help with the microprobe analyses. The authors highly appreciate thoughtful reviews by the Editor (Antonio Castro), Yaron Be’eri-Shlevin and Alexander Falster, which improved the manuscript.", revision_no = "9", abstract = "We present new field, petrographical, mineralogical and geochemical data from late Neoproterozoic pegmatites and aplites in southern Sinai, Egypt, at the northernmost limit of the Arabian-Nubian Shield. The pegmatites cross-cut host rocks in the Taba Metamorphic Complex (TMC) with sharp contacts and are divided into massive and zoned pegmatites. Massive pegmatites are the most common and form veins, dykes and masses of variable dimensions; strikes range mainly from E-W through NW-SE to N-S. Mineralogically, the massive pegmatites are divided into K-feldspar-rich and albite-rich groups. Zoned pegmatites occur as lenses of variable dimensions, featuring a quartz core, an intermediate zone rich in K-feldspars and an outer finer-grained zone rich in albite. All compositions are highly evolved and display geochemical characteristics of post-collisional A-type granites: high SiO_2, Na_2O+K_2O, FeO*/MgO, Ga/Al, Zr, Nb, Ga and Y alongside low CaO, MgO, Ba and Sr. They are rich in Rare Earth Elements (REE) and have extreme negative Eu anomalies (Eu/Eu*= 0.03–0.09). A genetic linkage between the pegmatites, aplites and alkali granite is confirmed by their common mild alkaline affinity and many other geochemical characteristics. These pegmatites and aplites represent the last small fraction of liquid remaining after extensive crystallization of granitic magma, injected along the foliation and into fractures of the host metamorphic rocks. The extensional tectonic regime and shallow depth of emplacement are consistent with a post-collisional environment.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/71087, title ="Late Ediacaran post-collisional A-type syenites with shoshonitic affinities, northern Arabian-Nubian Shield: a possible mantle-derived A-type magma", author = "Gahlan, Hisham and Asimow, Paul", journal = "Arabian Journal of Geosciences", volume = "9", number = "12", pages = "Art. No. 603", month = "August", year = "2016", doi = "10.1007/s12517-016-2629-x", issn = "1866-7511", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161014-090824859", note = "© 2016 Saudi Society for Geosciences. \n\nFirst Online: 19 August 2016.", revision_no = "6", abstract = "The Abu Rumeil syenitic rocks represent the inner ring dyke of the Katherina Ring complex, southern Sinai, Egypt. They are divided petrologically into two types, alkali feldspar syenite and quartz syenite. The mineralogy and geochemistry of the syenites indicate an alkaline nature with a shoshonitic affinity. Although rare mafic xenocrysts overgrown by primary K-feldspars and overlapping rare earth element (REE) patterns indicate some role for crustal contamination, the trace element chemistry shows a dominant mantle contribution. The geochronology and field relations imply that the Abu Rumeil syenites were emplaced in a post-collisional, within-plate tectonic setting, yet they express the enrichments in large-ion lithophile elements relative to high field strength elements generally characteristic of subduction influence. We suggest that this signature is inherited from partial melting of a lithospheric mantle source previously affected by subduction during assembly of the Arabian-Nubian Shield. Little evidence of the early evolution of the suite is preserved; there are no associated mafic rocks. We therefore restrict our attention to a petrogenetic model that can explain the relations among the observed felsic composition. The REE patterns of all samples are enriched in light REE and fractionated, but it is notable that there are small positive Eu anomalies in the alkali-feldspar syenites contrasting with small negative Eu anomalies in the quartz syenites. Positive Eu anomalies suggest a cumulate nature for the alkali-feldspar syenites; there are also breaks in the slopes of most variation trends between the alkali-feldspar syenites and the quartz syenites. The general trends in all major oxides and trace elements within the suite can be modeled by fractional crystallization of feldspars—with smaller roles for pyroxene, biotite, apatite, and Fe-Ti oxides—from an intermediate liquid to form the quartz syenites and by assimilation of the near-liquidus phases into the same starting liquid to form the alkali feldspar syenites. The geothermobarometry of pyroxenes and amphiboles suggests shallow emplacement (<10 km depth) and crystallization temperatures ranging from 1100 °C down to 800 °C.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/67876, title ="Shock synthesis of quasicrystals with implications for their origin in asteroid collisions", author = "Asimow, Paul D. and Lin, Chaney", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "113", number = "26", pages = "7077-7081", month = "June", year = "2016", doi = "10.1073/pnas.1600321113", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160613-121621550", note = "© 2016 National Academy of Sciences. \n\nEdited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved May 6, 2016 (received for review January 7, 2016) \n\nP.D.A. is supported by US National Science Foundation (NSF) Award EAR-1426526. L.B. is funded with the “60%2013” research funds from the University of Firenze, Italy. C.L. and P.J.S. are supported, in part, by NSF-MRSEC Program Grants DMR-0820341 through New York University and DMR-0819860 through the Princeton Center for Complex Materials. SEM, EDS, EBSD, and EPMA analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065. \n\nAuthor contributions: P.D.A. and P.J.S. designed research; P.D.A., C.L., L.B., C.M., and O.T. performed research; P.D.A., C.L., L.B., C.M., O.T., and L.S.H. analyzed data; and P.D.A., L.B., and P.J.S. wrote the paper. \n\nThe authors declare no conflict of interest. \n\nThis article is a PNAS Direct Submission. \n\nData deposition: Crystallographic data on quasicrystals is available from the authors upon request. \n\nThis article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1600321113/-/DCSupplemental.", revision_no = "19", abstract = "We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl_5, (Mg_(0.75)Fe^(2+)_(0.25))_2SiO_4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al_(68–73)Fe_(11–16)Cu_(10–12)Cr_(1–4)Ni_(1–2) and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/64290, title ="Enhanced East Pacific Rise hydrothermal activity during the last two glacial terminations", author = "Lund, D. C. and Asimow, P. D.", journal = "Science", volume = "351", number = "6272", pages = "478-482", month = "January", year = "2016", doi = "10.1126/science.aad4296", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160208-084848239", note = "© 2016 American Association for the Advancement of Science. \n\n14 September 2015; accepted 6 January 2016. \n\nWe dedicate this paper to J. Dymond, whose 1981 treatise on Nazca plate sediments made this work possible. We are also indebted to the Oregon State University Core Repository for carefully preserving the EPR sediment cores since they were collected in the early 1970s. We are grateful to L. Wingate at the University of Michigan and M. Cote at the University of Connecticut for technical support. This work has benefited from discussions with J. Granger, P. Vlahos, B. Fitzgerald, and M. Lyle. Data presented here are available on the National Oceanic and Atmospheric Administration’s Paleoclimatology Data website (www.ncdc.noaa.gov/data-access/paleoclimatology-data). Funding was provided by the University of Michigan and the University of Connecticut.", revision_no = "22", abstract = "Mid-ocean ridge magmatism is driven by seafloor spreading and decompression melting of the upper mantle. Melt production is apparently modulated by glacial-interglacial changes in sea level, raising the possibility that magmatic flux acts as a negative feedback on ice-sheet size. The timing of melt variability is poorly constrained, however, precluding a clear link between ridge magmatism and Pleistocene climate transitions. Here we present well-dated sedimentary records from the East Pacific Rise that show evidence of enhanced hydrothermal activity during the last two glacial terminations. We suggest that glacial maxima and lowering of sea level caused anomalous melting in the upper mantle and that the subsequent magmatic anomalies promoted deglaciation through the release of mantle heat and carbon at mid-ocean ridges.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/62485, title ="Don L. Anderson and the Caltech Seismo Lab", author = "Julian, Bruce R. and Asimow, Paul", number = "514", pages = "ix-xix", month = "October", year = "2015", doi = "10.1130/2015.2514(ix) ", url = "https://resolver.caltech.edu/CaltechAUTHORS:20151201-092238503", note = "© 2015 Geological Society of America. Attribution: You must attribute the work in the manner specified by the author or licensor (but no in any way that suggests that they endorse you or your use of the work). Noncommercial - you may not use this work for commercial purpose. No Derivative works - You may not alter, transform, or build upon this work. \n\nFirst published on September 11, 2015.", revision_no = "19", abstract = "The following reminiscences and recollections, scientific and otherwise, were contributed by Don Anderson’s scientific colleagues. Incomplete though they are, they give a flavor of the extraordinary range of Don’s activities, his influence on Earth science, and the phenomenon that was the Caltech Seismological Laboratory in his time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/61538, title ="Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp", author = "Fat’yanov, O. V. and Asimow, P. D.", journal = "Review of Scientific Instruments", volume = "86", number = "10", pages = "Art. No. 101502", month = "October", year = "2015", doi = "10.1063/1.4932578", issn = "0034-6748", url = "https://resolver.caltech.edu/CaltechAUTHORS:20151027-083623453", note = "© 2015 AIP Publishing LLC. \n\nReceived 23 January 2015; accepted 16 September 2015; published online 19 October 2015. \n\nThanks are due to the late Professor Tom Ahrens, the founder of the Lindhurst Laboratory of Experimental Geophysics at Caltech, for inviting one of us (O.V.F.) to join the research staff of this laboratory in 2006, for many interesting suggestions and advice, and for his broad interest in nontraditional methods in shock-wave physics including the topic of pyrometer calibration. Our LLNL collaborators, Dr. Neil Holmes and Dr. Jeff Nguyen, are gratefully acknowledged for their pyrometer and Pockels cell that largely extended the transient response characterization of our photodetectors. Professor George Rossman of Caltech helped with operating his visible range and FTIR spectrometers and shared his extensive knowledge about water contamination of minerals. Former technical staff members of the Lindhurst Lab Mike Long, Papo Gelle, and Russ Oliver provided expert assistance with the two-stage light-gas gun experiments. O.V.F. thanks his wife Elena who reviewed the very first draft of this manuscript and made the whole narrative substantially smoother. Valuable comments and suggestions by anonymous reviewers that helped improve the manuscript and made it more accessible are really appreciated. The financial support came from the U.S. NSF, Award No. EAR-1426526.", revision_no = "9", abstract = "We describe an accurate and precise calibration procedure for multichannel optical pyrometers such as the 6-channel, 3-ns temporal resolution instrument used in the Caltech experimental geophysics laboratory. We begin with a review of calibration sources for shock temperatures in the 3000-30\u2009000 K range. High-power, coiled tungsten halogen standards of spectral irradiance appear to be the only practical alternative to NIST-traceable tungsten ribbon lamps, which are no longer available with large enough calibrated area. However, non-uniform radiance complicates the use of such coiled lamps for reliable and reproducible calibration of pyrometers that employ imaging or relay optics. Careful analysis of documented methods of shock pyrometer calibration to coiled irradiance standard lamps shows that only one technique, not directly applicable in our case, is free of major radiometric errors. We provide a detailed description of the modified Caltech pyrometer instrument and a procedure for its absolute spectral radiance calibration, accurate to ±5%. We employ a designated central area of a 0.7× demagnified image of a coiled-coil tungsten halogen lamp filament, cross-calibrated against a NIST-traceable tungsten ribbon lamp. We give the results of the cross-calibration along with descriptions of the optical arrangement, data acquisition, and processing. We describe a procedure to characterize the difference between the static and dynamic response of amplified photodetectors, allowing time-dependent photodiode correction factors for spectral radiance histories from shock experiments. We validate correct operation of the modified Caltech pyrometer with actual shock temperature experiments on single-crystal NaCl and MgO and obtain very good agreement with the literature data for these substances. We conclude with a summary of the most essential requirements for error-free calibration of a fiber-optic shock-temperature pyrometer using a high-power coiled tungsten halogen irradiance standard lamp.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/58612, title ="Coordinated Hard Sphere Mixture (CHaSM): A simplified model for oxide and silicate melts at mantle pressures and temperatures", author = "Wolf, Aaron S. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "163", pages = "40-58", month = "August", year = "2015", doi = "10.1016/j.gca.2015.04.018", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150625-124954041", note = "© 2015 Elsevier Ltd. \n\nReceived 11 August 2014, Accepted 10 April 2015, Available online 22 April 2015. \n\nAssociate editor: Rajdeep Dasgupta. \n\nThe authors would like to thank Becky Lange, Youxue Zhang, Jean-Phillipe Harvey, Jennifer M. Jackson, and Jonathan Stebbins for useful conversations throughout the development of this study. We also would like to thank the NSF for supporting this work through awards EAR-1119522 and 1226270, and the Turner Postdoctoral Fellowship at the University of Michigan.", revision_no = "13", abstract = "We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme temperatures and pressures, including deep mantle conditions like those in the early Earth magma ocean. The Coordinated Hard Sphere Mixture (CHaSM) is based on an extension of the hard sphere mixture model, accounting for the range of coordination states available to each cation in the liquid. By utilizing approximate analytic expressions for the hard sphere model, this method is capable of predicting complex liquid structure and thermodynamics while remaining computationally efficient, requiring only minutes of calculation time on standard desktop computers. This modeling framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide range of pressures and temperatures. We find that the typical coordination number of the Mg cation evolves continuously upward from 5.25 at 0 GPa to 8.5 at 250 GPa. The results produced by CHaSM are evaluated by comparison with predictions from published first-principles molecular dynamics calculations, indicating that CHaSM is accurately capturing the dominant physics controlling the behavior of oxide melts at high pressure. Finally, we present a simple quantitative model to explain the universality of the increasing Grüneisen parameter trend for liquids, which directly reflects their progressive evolution toward more compact solid-like structures upon compression. This general behavior is opposite that of solid materials, and produces steep adiabatic thermal profiles for silicate melts, thus playing a crucial role in magma ocean evolution.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60061, title ="Current limitations of molecular dynamic simulations as probes of thermo-physical behavior of silicate melts", author = "Harvey, Jean-Phillipe and Asimow, Paul D.", journal = "American Mineralogist", volume = "100", number = "8-9", pages = "1866-1882", month = "August", year = "2015", doi = "10.2138/am-2015-5159", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150903-153606558", note = "© 2015 Mineralogical Society of America. Manuscript received August 11, 2014. Manuscript accepted February 16, 2015. \nManuscript handled by Keith Refson.\n\nJ.P.H. was supported by the Texaco Fellowship from Caltech and by the Natural Sciences and Engineering Research Council of Canada through the award PDF-438524-2013; P.D.A. was supported by the U.S. NSF through Geoinformatics award EAR-1226270. ", revision_no = "13", abstract = "Molecular dynamic simulations offer promise as an essential tool, complementary to experiments, for expanding the reach of computational thermodynamics in igneous petrology by evaluating excess thermodynamic properties of multicomponent silicate melts. However, we present evidence suggesting that current practices in simulation may not achieve the precision needed to predict complex phase equilibria relevant to modeling the Earth’s interior evolution. We highlight the importance of quantification of the chemical short-range order in terms of cation-cation pairs in the melt and its impact on different kinetic aspects of molecular dynamic simulations. We analyze published molecular dynamic simulation studies of silicate melts to identify specific criteria and best practices for achieving and demonstrating equilibrium and producing accurate results. Finally, we propose a list of experimental and numerical investigations that need to be performed in the future to ensure full consistency between these two approaches to reduce the gap in our fundamental understanding of silicate melts between the atomic level and the macroscopic scale. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/57004, title ="A self-consistent optimization of multicomponent solution properties: ab initio molecular dynamic simulations and the MgO-SiO_2 miscibility gap under pressure", author = "Harvey, Jean-Phillipe and Gheribi, Aïmen E.", journal = "Geochimica et Cosmochimica Acta", volume = "161", pages = "146-165", month = "July", year = "2015", doi = "10.1016/j.gca.2015.04.004", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150427-105640207", note = "© 2015 Elsevier B.V. Received 15 August 2014, Accepted 2 April 2015, Available online 13 April 2015.\n\nWe would like to thank Dr. James Sangster and Dr. Pierre Hudon for their constructive criticisms of the present work as well as the editors and reviewers at GCA for pushing us to improve the manuscript. This work was supported in part by Defence Research and Development Canada and by the US NSF through award EAR-1426526.", revision_no = "19", abstract = "We propose a new approach to parameterizing the Gibbs energy of a multicomponent solution as a function of temperature, pressure and composition. It uses the quasichemical model in the second nearest neighbour approximation and considers both a polynomial representation (for low pressure) and an exponential decay representation (for moderate-to-high pressure) of the excess molar volume v^(xs) to extend thermodynamic behaviour to elevated pressure. This approach differs from previous configuration-independent regular or associated solution-type models of multicomponent silicate liquids at elevated pressure and can account for any structural or short-range order data that may be available. A simultaneous least squares fit of the molar volume and the molar enthalpy of mixing data obtained from First Principles Molecular Dynamics (FPMD) simulations at various pressures enables complete parameterization of the excess thermodynamic properties of the solution. Together with consistently optimized properties of coexisting solids, this enables prediction of pressure-temperature-composition phase diagrams associated with melting. Although the method is extensible to natural multicomponent systems, we apply the procedure as a first test case to the important planetary model system MgO-SiO_2 using FPMD data found in the literature. One key result of this optimization, which depends only on the derived excess properties of the liquid phase, is that the consolute temperature of the SiO_2-rich miscibility gap is predicted to decrease with increasing pressure. This appears to be in disagreement with available experimental constraints and suggests possible thermodynamic inconsistency between FPMD data and experimental phase equilibrium data in the 0-5 GPa pressure range. We propose a new thermodynamic consistency criterion relating the signs of v^(xs) and other excess properties and discuss the need for precise calculations of derivatives of excess properties. Finally, the potential reappearance of the miscibility gap in the MgO-SiO_2 system above 5 GPa is discussed in light of this work.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/59822, title ="Reply to “Comment on ‘Molybdenum sound velocity and shear modulus softening under shock compression’ ”", author = "Nguyen, Jeffrey H. and Akin, Minta C.", journal = "Physical Review B", volume = "92", number = "2", pages = "Art. No. 026102", month = "July", year = "2015", doi = "10.1103/PhysRevB.92.026102", issn = "1098-0121", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150821-160740696", note = "©2015 American Physical Society. \n\n(Received 1 June 2015; published 27 July 2015) \n\nLawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC for the U.S. Department of Energy, National Nuclear Security Administration under Contract No. DE-AC52-07NA27344.", revision_no = "9", abstract = "We respond to the Comment by Errandonea et al. [Phys. Rev. B 92, 026101 (2015)] on their reinterpretation of our published data [Nguyen et al., Phys. Rev. B 89, 174109 (2014)]. In the original paper, we argued that there is no solid-solid phase transition along the Hugoniot at 2.1 Mbars. There is, however, a softening of the shear modulus starting at 2.6 Mbars. Errandonea et al. [Phys. Rev. B 92, 026101 (2015)] reinterpreted our data and concluded that there is a structural change near 2.3 Mbars on the Hugoniot. We will explore the differences and agreements in the two interpretations of our data.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/56775, title ="PRIMELT3 MEGA.XLSM software for primary magma calculation: Peridotite primary magma MgO contents from the liquidus to the solidus", author = "Herzberg, C. and Asimow, P. D.", journal = "Geochemistry, Geophysics, Geosystems", volume = "16", number = "2", pages = "563-578", month = "February", year = "2015", doi = "10.1002/2014GC005631 ", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150420-111623380", note = "© 2015 American Geophysical Union.\n\nReceived 23 OCT 2014; Accepted 29 JAN 2015; Accepted article online 5 FEB 2015; Published online 26 FEB 2015.\n\nWe are grateful to Mike Perfit for providing samples from the Siqueiros Fracture Zone and to Chris Vidito for electron microprobe analyses of the glasses. Paula Antoshechkina is acknowledged for helping with MELTS olivine liquidus temperatures. Keith Putirka is thanked for helping with an uncertainty analysis and for providing his database of experimental compositions. Jun-Ichi Kimura is thanked for pointing out an error in PRIMELT2 and for a critical review of this paper. Cin-Ty Lee is thanked for a critical reading and editorial handling of this paper. Data sources used to calculate primary magmas are given in Appendix A. PDA acknowledges NSF grant GI-1226270. Mike O’Hara\ncontributed to the thinking behind the PRIMELT model, and passed away during the submission of this paper.", revision_no = "19", abstract = "An upgrade of the PRIMELT algorithm for calculating primary magma composition is given together with its implementation in PRIMELT3 MEGA.xlsm software. It supersedes PRIMELT2.xls in correcting minor mistakes in melt fraction and computed Ni content of olivine, it identifies residuum mineralogy, and it provides a thorough analysis of uncertainties in mantle potential temperature and olivine liquidus temperature. The uncertainty analysis was made tractable by the computation of olivine liquidus temperatures as functions of pressure and partial melt MgO content between the liquidus and solidus. We present a computed anhydrous peridotite solidus in T-P space using relations amongst MgO, T and P along the solidus; it compares well with experiments on the solidus. Results of the application of PRIMELT3 to a wide range of basalts shows that the mantle sources of ocean islands and large igneous provinces were hotter than oceanic spreading centers, consistent with earlier studies and expectations of the mantle plume model.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/69205, title ="Dynamic Compression", author = "Asimow, P. D.", volume = "2", pages = "393-416", month = "January", year = "2015", doi = "10.1016/B978-0-444-53802-4.00050-6", isbn = "978-0-12-409548-9", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160725-143252967", note = "© 2015 Elsevier B.V.\n", revision_no = "11", abstract = "Dynamic compression methods, including shock wave and high-strain-rate studies, offer a range of insights into material properties of importance to geophysics and planetary science. Beyond direct studies of the flow and failure of projectiles and targets in impact and cratering processes, dynamic measurements of the equation of state, strength, thermodynamic functions, and phase boundaries of planetary materials at high pressure contribute essential constraints on the composition, physical state, and dynamical behavior of planetary interiors on all timescales. This chapter summarizes the physics of shock compression, experimental methods, and applications of dynamic material property measurements in geophysics and planetary science.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/53179, title ="Neoproterozoic boninite-series rocks in South China: A depleted mantle source modified by sediment-derived melt", author = "Zhao, Jun-Hong and Asimow, Paul D.", journal = "Chemical Geology", volume = "388", pages = "98-111", month = "November", year = "2014", doi = "10.1016/j.chemgeo.2014.09.004", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150105-112511328", note = "© 2014 Elsevier B.V. Received 9 March 2014, Revised 10 July 2014, Accepted 1 September 2014, Available online 11 September 2014. Editor: D.B. Dingwell.\n\nThis work was substantially supported by the National Nature Science Foundation of China (41073026, 41373016), FOK YING TONG Education Foundation, the Program for New Century Excellent Talents in University (NCET), and the Special Fund for Basic Scientific Research of Central Colleges, China University of Geosciences (Wuhan). PDA\nwas supported in part by the US National Science Foundation through award GI-1226270. Reviews by Donald Dingwell, Paul T. Robinson and an anonymous referee are gratefully acknowledged.", revision_no = "13", abstract = "A series of Neoproterozoic boninitic pillow lavas are hosted in Early Neoproterozoic strata along the southeastern margin of the Yangtze Block. These lavas record a period of subduction initiation during the secular evolution of South China. In this work we present analytical results from three units of pillow lavas (the Zhangyuan, Shexian and Lushan units) that form a common liquid line of descent with the previously reported 830-Ma boninites in the region, suggesting that they were produced by differentiation from similar parental melts. MELTS calculations show that major element compositions require fractionation of olivine + clinopyroxene + plagioclase + spinel from primary boninitic melts to have been accompanied by variable amounts of crustal contamination. The pillow lavas from the three localities show similar rare earth element patterns and arc-like primitive mantle normalized trace element patterns. They have high ^(206)Pb/^(204)Pb (18.41–19.33), ^(207)Pb/^(204)Pb (15.63–15.79) and ^(208)Pb/^(204)Pb ratios (38.78–40.26). Their ε_(Nd) values decrease from the Lushan lavas (+ 0.7 to + 1.9) to the Shexian lavas (− 0.5 to − 1.1) to the Zhangyuan lavas (− 4.0 to − 1.0), reaching values lower than the upper-level crustal contaminants and therefore indicating progressive enrichment of their sources by sediment melts. Compared with nearby but older (850 Ma) MORB-like tholeiitic basalts, which yield mantle potential temperature below 1400 °C and H_2O contents nearly 0.13 wt.%, the primary magmas of the boninite series rocks in this study were formed under higher pressures (3.5–1.0 GPa) and mantle potential temperatures (1440–1500 °C) with high H_2O contents (3420 to 4830 ppm), clear slab-derived sedimentary melt input, and harzburgite residues. The introduction of slab-derived water and sedimentary melt components into the mantle wedge at such high pressures, together with high temperatures and high degrees of melting, indicate that within a time span of only 20 million years after subduction initiation (850 to 830 Ma), the slab subducting under the southeastern margin of the Yangtze Block achieved substantial penetration to depth and interacted with hot overlying mantle, before subduction was abruptly ended by the amalgamation of the Yangtze and Cathaysia blocks.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50734, title ="Seconds after Impact: Insights from Diffusion between Lechatelierite and Host Glass in Tektites and Experiments", author = "Macris, C. A. and Badro, J.", journal = "Meteoritics and Planetary Science", volume = "49", number = "S1", pages = "A253", month = "September", year = "2014", issn = "1086-9379", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141023-105706037", note = "© 2014 The Meteoritical Society.\n\nArticle first published online: 8 Sep. 2014.", revision_no = "11", abstract = "Tektites are natural glasses formed as a result\nof melting and quenching of distally ejected terrestrial material\nupon hypervelocity (>11 km/s) impact on Earth. Some tektites\ncontain inclusions of lechatelierite (nearly pure SiO_2 glass; 99-100 wt. % SiO_2), generally thought to be the amorphous relicts of\npartially digested quartz grains [1]. This study exploits the\npresence of these local heterogeneities to extract information\nabout tektite thermal histories by investigating chemical diffusion\nbetween molten silica inclusions and surrounding peraluminous\nfelsic melt in natural tektites and experimental analogues.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46244, title ="Continental rift and oceanic protoliths of mafic–ultramafic rocks from the Kechros Complex, NE Rhodope (Greece): implications from petrography, major and trace-element systematics, and MELTS modeling", author = "Baziotis, I. and Mposkos, E.", journal = "International Journal of Earth Sciences", volume = "103", number = "4", pages = "981-1003", month = "June", year = "2014", doi = "10.1007/s00531-014-1007-8", issn = "1437-3254", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140612-124914109", note = "© 2014 Springer-Verlag Berlin Heidelberg. \n\nReceived: 9 July 2013; Accepted: 15 February 2014; Published online: 7 March 2014.", revision_no = "16", abstract = "The whole-rock chemistry of eclogites, partially amphibolitized eclogites, and dyke amphibolites from the metamorphic Kechros complex in the eastern Rhodope Mountains preserves evidence of the geodynamic framework for the origin of their protoliths. Major and trace-element concentrations define two distinct protolith groups for the eclogites. The low-Fe–Ti (LFT) eclogites have low-TiO_2 content (<0.67 wt%), negative high field strength element anomalies, and variable enrichments in large ion lithophile elements (LILE). The rare earth element (REE) patterns are characterized by strong light-REE (LREE) enrichment and heavy-REE (HREE) depletion. The high-Fe–Ti (HFT) eclogites have small to moderate LILE enrichment and lack Nb anomalies. The REE patterns of the HFT eclogites are characterized by LREE depletion and relatively flat MREE–HREE patterns. The rock compositions and petrographic features of the LFT eclogites resemble gabbros formed in a continental rift environment with minor to moderate contamination of a mantle-derived mafic magma by continental crust, whereas the HFT eclogites resemble mafic rocks formed in extensional oceanic environments. We interpret the HFT suite to represent a later stage in an evolution from continental rift to open ocean, following the origin of the LFT suite. Dyke amphibolite compositions, except for probable SiO_2 loss associated with metamorphic dehydration reactions, appear to represent liquid compositions quenched in conduits through the lower crust. MELTS modeling shows that dyke amphibolite compositions can be related to each other by fractional crystallization under strongly oxidizing conditions at ~0.5 GPa pressure, and all can be derived from a low-degree melt of modified fertile peridotite from around 1.7 GPa. Cumulates crystallized from the parental liquids of the amphibolites under oxidizing conditions may have yielded the protoliths of the HFT suite.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46236, title ="Molybdenum sound velocity and shear modulus softening under shock compression", author = "Nguyen, Jeffrey H. and Akin, Minta C.", journal = "Physical Review B", volume = "89", number = "17", pages = "Art. No. 174109 ", month = "May", year = "2014", doi = "10.1103/PhysRevB.89.174109 ", issn = "1098-0121", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140612-102504287", note = "© 2014 American Physical Society.\nReceived 30 August 2013; revised manuscript received 1 May 2014; published 21 May 2014.\nWe thank R. Hixson and M. Ross for their useful\ndiscussions, and Papo Gelle, Mike Long, Russ Oliver,\nBob Nafzinger, Paul Benevento, Sam Weaver, and Cory\nMcLean for their dedicated effort. Lawrence Livermore\nNational Laboratory is operated by Lawrence Livermore\nNational Security, LLC, for the U.S. Department of Energy,\nNational Nuclear Security Administration under Contract\nDE-AC52-07NA27344.", revision_no = "10", abstract = "We measured the longitudinal sound velocity in Mo shock compressed up to 4.4 Mbars on the Hugoniot. Its sound speed increases linearly with pressure up to 2.6 Mbars; the slope then decreases up to the melting pressure of ∼3.8 Mbars. This suggests a decrease of shear modulus before the melt. A linear extrapolation of our data to 1 bar agrees with the ambient sound speed. The results suggest that Mo remains in the bcc phase on the Hugoniot up to the melting pressure. There is no statistically significant evidence for a previously reported bcc→hcp phase transition on the Hugoniot.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47545, title ="MgO melting curve constraints from shock temperature and rarefaction overtake measurements in samples preheated to 2300 K", author = "Fat'yanov, Oleg V. and Asimow, P. D.", journal = "Journal of Physics: Conference Series", volume = "500", number = "6", pages = "Art. No. 062003", month = "May", year = "2014", doi = "10.1088/1742-6596/500/6/062003", issn = "1742-6596", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140729-082224529", note = "© 2014 the authors. \n\nContent from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd. \n\nWe are grateful to the late Prof. Thomas J. Ahrens for his deep interest and enthusiastic support of this research to the last days of his life. We thank M. Long, E. Gelle, and R. Oliver for technical help with our experiments. OVF thanks his newborn son Vladimir for the opportunity to finish\nwriting and to submit this manuscript. Funded by NSF awards EAR-1119522 and EAR-1050269.", revision_no = "13", abstract = "Continuing our effort to obtain experimental constraints on the melting curve of MgO at 100-200 GPa, we extended our target preheating capability to 2300 K. Our new Mo capsule design holds a long MgO crystal in a controlled thermal gradient until impact by a Ta flyer launched at up to 7.5 km/s on the Caltech two-stage light-gas gun. Radiative shock temperatures and rarefaction overtake times were measured simultaneously by a 6-channel VIS/NIR pyrometer with 3 ns time resolution. The majority of our experiments showed smooth monotonic increases in MgO sound speed and shock temperature with pressure from 197 to 243 GPa. The measured temperatures as well as the slopes of the pressure dependences for both temperature and sound speed were in good agreement with those calculated numerically for the solid phase at our peak shock compression conditions. Most observed sound speeds, however, were ~800 m/s higher than those predicted by the model. A single unconfirmed data point at 239 GPa showed anomalously low temperature and sound speed, which could both be explained by partial melting in this experiment and could suggest that the Hugoniot of MgO preheated to 2300 K crosses its melting line just slightly above 240 GPa.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45612, title ="High frequency seismic waves and slab structures beneath Italy", author = "Sun, Daoyuan and Miller, Meghan S.", journal = "Earth and Planetary Science Letters", volume = "391", pages = "212-223", month = "April", year = "2014", doi = "10.1016/j.epsl.2014.01.034", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140508-135028711", note = "© 2014 Elsevier B.V. Received 31 October 2013. Received in revised form 18 January 2014. Accepted 24 January 2014.\nAvailable online 19 February 2014. Editor: P. Shearer. The authors would like to thank the editor and two reviewers for their suggestions and comments. We also thank Don Anderson, Don Helmberger, and The-Ru Alex Song for stimulating conversations and communications. This work was supported by funding provided by NSF CAREER award (EAR-1054638) and USC postdoctoral scholar research grant. A special thanks to Dr. Giulio Selvaggi, director of INGV-CNT, and Centro Nazionale Terremoti for providing the data. NPA research is supported by Science Foundation Ireland & the Marie-Curie Action COFUND under Grant Number 11/SIRG/E2174.", revision_no = "17", abstract = "Tomographic images indicate a complicated subducted slab structure beneath the central Mediterranean where gaps in fast velocity anomalies in the upper mantle are interpreted as slab tears. The detailed shape and location of these tears are important for kinematic reconstructions and understanding the evolution of the subduction system. However, tomographic images, which are produced by smoothed, damped inversions, will underestimate the sharpness of the structures. Here, we use the records from the Italian National Seismic Network (IV) to study the detailed slab structure. The waveform records for stations in Calabria show large amplitude, high frequency (f>5 Hz) late arrivals with long coda after a relatively low-frequency onset for both P and S waves. In contrast, the stations in the southern and central Apennines lack such high frequency arrivals, which correlate spatially with the central Apennines slab window inferred from tomography and receiver function studies. Thus, studying the high frequency arrivals provides an effective way to investigate the structure of slab and detect possible slab tears. The observed high frequency arrivals in the southern Italy are the strongest for events from 300 km depth and greater whose hypocenters are located within the slab inferred from fast P-wave velocity perturbations. This characteristic behavior agrees with previous studies from other tectonic regions, suggesting the high frequency energy is generated by small scale heterogeneities within the slab which act as scatterers. Furthermore, using a 2-D finite difference (FD) code, we calculate synthetic seismograms to search for the scale, shape and velocity perturbations of the heterogeneities that may explain features observed in the data. Our preferred model of the slab heterogeneities beneath the Tyrrhenian Sea has laminar structure parallel to the slab dip and can be described by a von Kármán function with a down-dip correlation length of 10 km and 0.5 km in thickness with ∼2.5% V_p fluctuations within the slab. This suggests that the heterogeneities are inherited from the melt shear bands formed during the original formation of the oceanic lithosphere near the mid-ocean ridge.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45239, title ="Zonation of H_(2)O and F Concentrations around Melt Inclusions in Olivines", author = "Le Voyer, Marion and Asimow, Paul D.", journal = "Journal of Petrology", volume = "55", number = "4", pages = "685-707", month = "April", year = "2014", doi = "10.1093/petrology/egu003", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140428-094609669", note = "© The Author 2014. Published by Oxford University Press. \n\nReceived April 27, 2013; Accepted January 6, 2014. \n\nWe thank Chi Ma for help with the electron microprobe and EBSD analyses. Reviews by T. J. Tenner, A. E. Saal, J. D. Webster and Editor W. A. Bohrson helped to improve the paper and were gratefully appreciated. This work was supported by a grant from the Gordon and Betty Moore Foundation to the Caltech Microanalysis Center.", revision_no = "27", abstract = "Studies of both naturally quenched and experimentally reheated melt inclusions have established that they can lose or gain H_(2)O after entrapment in their host mineral, before or during eruption. Here we report nanoSIMS analyses of H2O, Cl and F in olivine around melt inclusions from two natural basaltic samples: one from the Sommata cinder cone on Vulcano Island in the Aeolian arc and the other from the Jorullo cinder cone in the Trans-Mexican Volcanic Belt. Our results constrain olivine/basaltic melt partition coefficients and allow assessment of mechanisms of volatile loss from melt inclusions in natural samples. Cl contents in olivine from both samples are mostly below detection limits (≤0·03 ± 0·01 ppm), with no detectable variation close to the melt inclusions. Assuming a maximum Cl content of 0·03 ppm for all olivines, maximum estimates for Cl partition coefficients between olivine and glass are 0·00002 ± 0·00002. Olivines from the two localities display contrasting H_(2)O and F compositions: Sommata olivines contain 27 ± 11 ppm H_(2)O and 0·28 ± 0·07 ppm F, whereas Jorullo olivines have lower and proportionately more variable H_(2)O and F (11 ± 12 ppm and 0·12 ± 0·09 ppm, respectively; uncertainties are two standard deviations for the entire population). The variations of H_(2)O and F contents in the olivines exhibit clear zonation patterns, increasing with proximity to melt inclusions. This pattern was most probably generated during transfer of volatiles out of the inclusions through the host olivine. H_(2)O concentration gradients surrounding melt inclusions are roughly concentric, but significantly elongated parallel to the crystallographic a-axis of olivine. Because of this preferential crystallographic orientation, this pattern is consistent with H_(2)O loss that is rate-limited by the ‘proton–polaron’ mechanism of H diffusion in olivine. Partition coefficients based on olivine compositions immediately adjacent to melt inclusions are 0·0007 ± 0·0003 for H_(2)O and 0·0005 ± 0·0003 for F. The H_(2)O and F diffusion profiles most probably formed in response to a decrease in the respective fugacities in the external melt, owing to either degassing or mixing with volatile-poor melt. Volatile transport out of inclusions might also have been driven in part by increases in the fugacity within the inclusion owing to post-entrapment crystallization. In the case of F, because of the lack of data on F diffusion in olivine, any interpretation of the measured F gradients is speculative. In the case of H_(2)O, we model the concentration gradients using a numerical model of three-dimensional anisotropic diffusion of H, where initial conditions include both H2O decrease in the external melt and post-entrapment enrichment of H_(2)O in the inclusions. The model confirms that external degassing is the dominant driving force, showing that the orientation of the anisotropy in H diffusion is consistent with the proton–polaron diffusion mechanism in olivine. The model also yields an estimate of the initial H_(2)O content of the Sommata melt inclusions before diffusive loss of 6 wt % H_(2)O. The findings provide new insights on rapid H_(2)O loss during magma ascent and improve our ability to assess the fidelity of the H_(2)O record from melt inclusions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45754, title ="A lesson in defining \"extinct\"", author = "Asimow, Paul D.", journal = "Physics Today", volume = "67", number = "1", pages = "8", month = "January", year = "2014", doi = "10.1063/PT.3.2227", issn = "0031-9228", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140515-080328952", note = "© 2014 American Institute of Physics.", revision_no = "9", abstract = "Toni Feder’s Issues and Events news item about the High-Altitude Water Cherenkov Gamma-Ray Observatory under construction in Mexico ( Physics Today, October 2013, page 22) begins by describing the site as “nestled at 4100 m on the slopes of Sierra Negra, an extinct volcano.” However, as the picture accompanying her piece or a cursory examination in Google Earth makes clear, the site is not on the slopes of Sierra Negra. It sits in the saddle between Sierra Negra and its much larger companion Pico de Orizaba, also known as Citlaltépetl. Sierra Negra, a minor flank cone of that larger volcanic system, may now be extinct, but Pico de Orizaba (http://www.volcano.si.edu/volcano.cfm?vnum=1401-10=) absolutely is not. It is dormant at best, having erupted as recently as 1846. \n\nTo compound the issue, the photograph shows that the observatory site is built squarely in front of an obviously young lava flow. Now, I’m sure that site selection was done with due attention to natural hazards, but as long as astronomers insist on building expensive observatories on top of volcanoes, there needs to be clear understanding and common vocabulary between astronomers and geologists. “Extinct” is a troublesome word when applied to a volcano.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/43400, title ="Generation of talc in the mantle wedge and its role in subduction dynamics in central Mexico", author = "Kim, YoungHee and Clayton, Robert W.", journal = "Earth and Planetary Science Letters", volume = "384", pages = "81-87", month = "December", year = "2013", doi = "10.1016/j.epsl.2013.10.006", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140116-090617911", note = "© 2013 Elsevier B.V.\nReceived 13 August 2013;\nReceived in revised form 3 October 2013;\nAccepted 4 October 2013;\nAvailable online 27 October 2013.\nEditor: P. Shearer\n\nThis work was funded by the Korea Meteorological Administration Research and Development Program under Grant CATER-2013-8010. This study was also supported by the Gordon and Betty Moore Foundation through the Tectonics Observatory at California Institute of Technology (Contribution number 223) and NSF award EAR 0609707. We used Excel Worksheets and Macros from Hacker and Abers (2004) for calculating seismic speeds. We thank Xyoli Perez-Campos, Arturo Iglesias, and others at the Universidad Nacional Autonoma de Mexico for deploying and maintaining the MASE line. We also thank Joann Stock and Michael Gurnis from California Institute of Technology for discussions. Finally, we thank Editor Peter Shearer, Pascal Audet, and one anonymous reviewer for helpful comments which improved the manuscript.", revision_no = "13", abstract = "Geophysical evidence shows the presence of low-seismic velocity material at the surface of slabs in subduction zones. In the central Mexican subduction zone this appears as a thin (∼4 km) low-velocity zone that absorbs nearly all of the strain. The P-to-S velocity ratio as a function of S wave velocity distinguishes among the various candidate hydrous (low-strength) minerals; the thin layer in the flat-slab region is most consistent with a layer showing enrichment in talc overlying normal MORB-like gabbro. Based on available thermodynamic data for equilibria for talc, its generation at the trench is nearly impossible, and hence we propose it originates from the mantle wedge during the slab flattening process coupled with trench rollback. The evolution of this low-strength zone has important implications for the dynamics of the slab-flattening process as well as the geochemistry of the mantle wedge and arc in central Mexico.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/43357, title ="Direct shock compression experiments on premolten forsterite and progress toward a consistent high-pressure equation of state for CaO-MgO-Al_2O_3-SiO_2-FeO liquids", author = "Thomas, Claire W. and Asimow, Paul D.", journal = "Journal of Geophysical Research. Solid Earth", volume = "118", number = "11", pages = "5738-5752", month = "November", year = "2013", doi = "10.1002/jgrb.50374", issn = "2169-9313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140114-104523180", note = "© 2013 American Geophysical Union. Received 28 March 2013; revised 7 August 2013; accepted 13 September 2013; published 11 November 2013. The authors would like to thank the shock\nwave lab technical staff—Oleg Fat’yanov, Eprapodito Gelle, and Russel Oliver, and also Denis Andrault and an anonymous reviewer for their helpful comments. This work was supported by the National Science Foundation through award EAR-1119522. ", revision_no = "16", abstract = "We performed shock compression experiments on preheated forsterite liquid (Mg_2SiO_4) at an initial temperature of 2273\u2009K and have revised the equation of state (EOS) that was previously determined by shock melting of initially solid Mg_2SiO_4 (300\u2009K). The linear Hugoniot, U_S\u2009=\u20092.674\u2009±\u20090.188\u2009+\u20091.64\u2009±\u20090.06 u_p km/s, constrains the bulk sound speed within a temperature and composition space as yet unexplored by 1\u2009bar ultrasonic experiments. We have also revised the EOS for enstatite liquid (MgSiO_3) to exclude experiments that may have been only partially melted upon shock compression and also the EOS for anorthite (CaAl_2SiO_6) liquid, which now excludes potentially unrelaxed experiments at low pressure. The revised fits and the previously determined EOS of fayalite and diopside (CaMg_2SiO_6) were used to produce isentropes in the multicomponent CaO-MgO-Al_2O_3-SiO_2-FeO system at elevated temperatures and pressures. Our results are similar to those previously presented for peridotite and simplified “chondrite” liquids such that regardless of where crystallization first occurs, the liquidus solid sinks upon formation. This process is not conducive to the formation of a basal magma ocean. We also examined the chemical and physical plausibility of the partial melt hypothesis to explain the occurrence and characteristics of ultra-low velocity zones (ULVZ). We determined that the ambient mantle cannot produce an equilibrium partial melt and residue that is sufficiently dense to be an ultra-low velocity zone mush. The partial melt would need to be segregated from its equilibrium residue and combined with a denser solid component to achieve a sufficiently large aggregate density.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/89633, title ="Novel Applications of Knudsen Effusion Mass Spectrometry", author = "Jacobson, N. S. and Hurowitz, J. A.", journal = "ECS Transactions", volume = "58", number = "3", pages = "3-12", month = "October", year = "2013", doi = "10.1149/05803.0003ecst", issn = "1938-6737", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180914-100810777", note = "© 2013 ECS - The Electrochemical Society. \n\nIt is a pleasure to thank Dr. Evan Copland, formerly at NASA GRC, now with CSIRO, Sydney, Australia for his design of the multiple cell flange and many contributions to high temperature mass spectrometry at the Glenn Research Center.", revision_no = "9", abstract = "Knudsen effusion mass spectrometry (KEMS) is a valuable and versatile tool in physical chemistry, materials science, and geology. Most of the applications center on thermodynamic measurements. In this paper two novel applications of KEMS are discussed. The first is the determination of K isotope ratios for application to K-Ar dating. The second is the determination of silica thermodynamic activities in silicates via a reducing agent to increase signals without changing the condensed phase composition. This also involves the measurement of vaporization coefficient via a multi-cell KEMS method.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42228, title ="Preheated shock experiments in the molten CaAl_2Si_2O_8-CaFeSi_2O_6-CaMgSi_2O_6 ternary: A test for linear mixing of liquid volumes at high pressure and temperature", author = "Thomas, Claire W. and Asimow, Paul D.", journal = "Journal of Geophysical Research. Solid Earth", volume = "118", number = "7", pages = "3354-3365", month = "July", year = "2013", doi = "10.1002/jgrb.50269 ", issn = "2169-9313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131104-141737237", note = "© 2013 American Geophysical Union.\n\nReceived 1 April 2013; revised 21 June 2013; accepted 25 June 2013; published 24 July 2013.\n\nThe authors would like to thank the following:\nthe shock wave lab technical staff—Oleg Fat’yanov, Eprapodito Gelle,\nRussel Oliver, and Emma Dodd. Thanks to X. Guo and R. A. Lange for their\nongoing collaboration and willingness to share their manuscripts. This work\nwas supported by the National Science Foundation through award EAR-1119522.", revision_no = "15", abstract = "We performed 17 new shock wave experiments on preheated (1673 K) hedenbergite liquid (CaFeSi_2O_6) and two model basalt liquids (an equimolar binary mix of CaAl_2Si_2O_8 + CaFeSi_2O_6 and an equimolar ternary mix of CaAl_2Si_2O_8 + CaFeSi_2O_6 +CaMgSi_2O_6) in order to determine their equations of state (EOS). Ambient pressure density measurements on these and other Fe-bearing silicate liquids indicate that FeO has a partial molar volume that is highly dependent on composition, which leads to large errors in estimates of the densities of Fe-bearing liquids at ambient pressure based on an ideal mixing of any fixed set of end-member liquids. We formulated a series of mixing tests using the EOS determined in this study to examine whether ideal mixing of volumes might nevertheless suffice to describe the ternary system CaAl_2Si_2O_8-CaFeSi_2O_6-CaMgSi_2O_6 at high temperature and pressure. The ideal mixing null hypothesis is rejected; compositional variations in partial molar volume of FeO appear to extend to high pressure. Only densities of Fe-bearing liquid mixtures with oxide mole fraction of FeO less than 0.06 can be adequately approximated using an ideal solution.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/38537, title ="A double-spike method for K–Ar measurement: A technique\nfor high precision in situ dating on Mars and other\nplanetary surfaces", author = "Farley, K. A. and Hurowitz, J. A.", journal = "Geochimica et Cosmochimica Acta", volume = "110", pages = "1-12", month = "June", year = "2013", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130516-095248373", note = "© 2013 Elsevier Ltd. Received 4 December 2012; accepted in revised form 5 February 2013; available online 16 February 2013. We thank Paul Renne for suggesting and providing the Viluy Traps basalt sample and Tim Becker for facilitating the irradiation of our spike glass. We thank Leah Morgan, Pete Burnard, and two anonymous reviewers for helpful suggestions. This work could not have occurred without the generous and patient support of the Keck Institute for Space Studies. This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Agency (JAH).\nAssociate editor: Pete Burnard", revision_no = "12", abstract = "A new method for K–Ar dating using a double isotope dilution technique is proposed and demonstrated. The method is designed to eliminate known difficulties facing in situ dating on planetary surfaces, especially instrument complexity and power availability. It may also have applicability in some terrestrial dating applications. Key to the method is the use of a solid tracer spike enriched in both ^(39)Ar and ^(41)K. When mixed with lithium borate flux in a Knudsen effusion cell, this tracer spike and a sample to be dated can be successfully fused and degassed of Ar at <1000 °C. The evolved ^(40)Ar^∗/^(39)Ar ratio can be measured to high precision using noble gas mass spectrometry. After argon measurement the sample melt is heated to a slightly higher temperature (∼1030 °C) to volatilize potassium, and the evolved ^(39)K/(41)K ratio measured by Knudsen effusion mass spectrometry. Combined with the known composition of the tracer spike, these two ratios define the K–Ar age using a single sample aliquot and without the need for extreme temperature or a mass determination. In principle the method can be implemented using a single mass spectrometer.\nExperiments indicate that quantitative extraction of argon from a basalt sample occurs at a sufficiently low temperature that potassium loss in this step is unimportant. Similarly, potassium isotope ratios measured in the Knudsen apparatus indicate good sample-spike equilibration and acceptably small isotopic fractionation. When applied to a flood basalt from the Viluy Traps, Siberia, a K–Ar age of 351 ± 19 Ma was obtained, a result within 1% of the independently known age. For practical reasons this measurement was made on two separate mass spectrometers, but a scheme for combining the measurements in a single analytical instrument is described. Because both parent and daughter are determined by isotope dilution, the precision on K–Ar ages obtained by the double isotope dilution method should routinely approach that of a pair of isotope ratio determinations, likely better than ±5%.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/36826, title ="Nickel and helium evidence for melt above the core–mantle boundary", author = "Herzberg, Claude and Ionov, Dmitri A.", journal = "Nature", volume = "493", number = "7432", pages = "393-397", month = "January", year = "2013", doi = "10.1038/nature11771", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130208-132039113", note = "© 2013 Macmillan Publishers Limited. \n\nReceived: 10 May 2012; Accepted: 05 November 2012; Published online: 09 January 2013.\n\nC.H. thanks L. Larsen, M. Portnyagin, A. Sobolev and D. Walker for discussions. We are very grateful to R. Walker for a critical review. D.A.I. acknowledges PNP grants from the French INSU-CNRS in 2010-2012 and P.D.A. acknowledges NSF grant EAR-1119522. P.D.A. thanks A. Matzen for extended discussions. D.G.’s work is funded by NSF grant EAR1145271.\n\n\nAuthor Contributions: C.H. modelled olivine compositions and developed a variety of\nmagma ocean and core–mantle interaction interpretations. P.D.A. suggested the core–\nmantle interaction model in its current form and critiqued all Ni partitionmodels. D.A.I.\nprovided high-precision olivine and whole-rock analyses for mantle peridotite. C.V.\nacquired high-precision olivine data for Fernandina (Galapagos). M.G.J. provided\ninformation on Pb, Nd and He isotopes. D.G. provided rock samples from Fernandina.\nAll authors contributed to the intellectual growth of this paper.", revision_no = "24", abstract = "High ^(3)He/^(4)He ratios in some basalts have generally been interpreted as originating in an incompletely degassed lower-mantle source. This helium source may have been isolated at the core–mantle boundary region since Earth’s accretion. Alternatively, it may have taken part in whole-mantle convection and crust production over the age of the Earth; if so, it is now either a primitive refugium at the core–mantle boundary or is distributed throughout the lower mantle. Here we constrain the problem using lavas from Baffin Island, West Greenland, the Ontong Java Plateau, Isla Gorgona and Fernandina (Galapagos). Olivine phenocryst compositions show that these lavas originated from a peridotite source that was about 20 per cent higher in nickel content than in the modern mid-ocean-ridge basalt source. Where data are available, these lavas also have high ^(3)He/^(4)He. We propose that a less-degassed nickel-rich source formed by core–mantle interaction during the crystallization of a melt-rich layer or basal magma ocean, and that this source continues to be sampled by mantle plumes. The spatial distribution of this source may be constrained by nickel partitioning experiments at the pressures of the core–mantle boundary.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/36898, title ="The molar volume of FeO–MgO–Fe_2O_3–Cr_2O_3–Al_2O_3–TiO_2\nspinels", author = "Hamecher, Emily A. and Antoshechkina, Paula M.", journal = "Contributions to Mineralogy and Petrology", volume = "165", number = "1", pages = "25-43", month = "January", year = "2013", doi = "10.1007/s00410-012-0790-0", issn = "0010-7999", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130213-110442261", note = "© 2012 Springer-Verlag. \n\nReceived: 28 September 2011. Accepted: 31 July 2012. Published online: 24 August 2012. \n\nCommunicated by J. Blundy. \n\nWe wish to thank Peter Luffi for identifying the garnet solid solution error in the original MELTS code, Ashley Nagle for pointing out the anomalously low spinel–garnet transition pressures obtained when the corrected garnet model is used, and Aaron Wolf for helpful discussions regarding statistical analysis. Comments by Associate Editor Jon Blundy are greatly appreciated, as are the reviews of two anonymous reviewers. This work was supported by the National Science Foundation and the American Recovery and Reinvestment Act through award 0838244.", revision_no = "30", abstract = "We define and calibrate a new model of molar volume as a function of pressure, temperature, ordering state, and composition for spinels in the supersystem (Mg, Fe^(2+))(Al, Cr, Fe^(3+))_2O_4 − (Mg, Fe^(2+))_2TiO_4. We use 832 X-ray and neutron diffraction measurements performed on spinels at ambient and in situ high-P, T conditions to calibrate end-member equations of state and an excess volume model for this system. The effect on molar volume of cation ordering over the octahedral and tetrahedral sites is captured with linear dependence on Mg^(2+), Al^(3+), and Fe^(3+) site occupancy terms. We allow standard-state volumes and coefficients of thermal expansion of the end members to vary within their uncertainties during extraction of the mixing properties, in order to achieve the best fit. Published equations of state of the various spinel end members are analyzed to obtain optimal values of the bulk modulus and its pressure derivative, for each explicit end member. For any spinel composition in the supersystem, the model molar volume is obtained by adding excess volume and cation order-dependent terms to a linear combination of the five end-member volumes, estimated at pressure and temperature using the high-T Vinet equation of state. The preferred model has a total of 9 excess volume and order-dependent parameters and fits nearly all experiments to within 0.02 J/bar/mol, or better than 0.5 % in volume. The model is compared to the current MELTS spinel model with a demonstration of the impact of the model difference on the estimated spinel-garnet lherzolite transition pressure.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/36136, title ="From basalts to boninites: The geodynamics of volcanic expression during induced subduction initiation", author = "Leng, Wei and Gurnis, Michael", journal = "Lithosphere", volume = "4", number = "6", pages = "511-523", month = "December", year = "2012", issn = "1941-8264", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130103-085750674", note = "© 2012 Geological Society of America.\nManuscript Received 29 March 2012; Revised Manuscript Received 20 August 2012; Manuscript Accepted 28 September 2012.\nPublished online 26 October 2012.\nWe thank Bob Stern and two anonymous\nreviewers, whose comments help to improve the\nmanuscript. Leng was supported by the O.K.\nEarl Fellowship at Caltech. Additional support\nwas provided by the National Science Foundation\n(EAR-0810303) and the Caltech Tectonics\nObservatory (by the Gordon and Betty Moore\nFoundation) with contribution number TO 209.", revision_no = "15", abstract = "Subduction initiation may unfold via different pathways in response to plate strength, plate age, and driving mechanism. Such pathways influence volcanism on the overriding plate and may be preserved in the sequence of erupted volcanic products. Here, we parameterize melting in a mechanical model to determine the volcanic products that form in response to different subduction initiation modes. We find that with a mode of continuous initiation with infant-arc spreading, the foundering of the subducting slab and water release from the slab govern a succession from basalts with compositions similar to mid-ocean-ridge basalts (MORB) to boninites. The modeled transition from MORB-like to boninite composition typically occurs within a few million years. When plate strength is reduced, the subducting slab tends to segment, with extensive melting occurring when the slab breaks; most melting occurs close to the trench. When plate strength increases, subduction initiation becomes continuous without infant-arc spreading; such a mode leads to a limited, very low degree of melting occurring during a long interval of plate convergence before subduction initiation starts, although extensive melting near the trench is still possible when subduction initiation starts after a protracted period of plate convergence (∼10 m.y.). If the subduction initiation is driven by constant stresses, such as through ridge push, the slab subducts rapidly in response to continuous acceleration of the plate under action of the far-field push; significant melting, including boninite eruption, can be generated within a few million years with no trench migration. Based on the tectonic and volcanic evolution, these different modes may be applicable to the initiation of the Izu-Bonin-Mariana arc (infant-arc spreading and a sequence from MORB-like to boninites), the New Hebrides arc (slab segments in the upper mantle), the Puysegur Trench in New Zealand (scarce distribution of volcanism and no infant-arc spreading), and the Aleutian Trench (strong volcanism and no infant-arc spreading). ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35509, title ="Multi-technique equation of state for Fe_(2)SiO_4 melt and the density of Fe-bearing silicate melts from 0 to 161 GPa", author = "Thomas, Claire W. and Liu, Qiong", journal = "Journal of Geophysical Research B", volume = "117", pages = "Art. No. B10206 ", month = "October", year = "2012", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121116-100605844", note = "© 2012 American Geophysical Union. \n\nReceived 26 April 2012; revised 12 August 2012; accepted 27 August 2012; published 12 October 2012.\n\nThe authors would like to thank the shock wave lab technical staff—Michael Long, Eprapodito Gelle, and Russell\nOliver; additionally, Bjorn Mysen for conducting Mössbauer measurements and Jeff Nguyen for running simulations of our shock wave experiments. C.B.A. acknowledges Michael Spilde for assistance with electron microprobe analyses and Galen Barnett for assistance with multi-anvil experiments.\nThis work was supported by the National Science Foundation\nthrough award EAR-0855774.", revision_no = "17", abstract = "We have conducted new equation of state measurements on liquid Fe_(2)SiO_4 in a collaborative, multi-technique study. The liquid density (ρ), the bulk modulus (K), and its pressure derivative (K′) were measured from 1 atm to 161 GPa using 1-atm double-bob Archimedean, multi-anvil sink/float, and shock wave techniques. Shock compression results on initially molten Fe_(2)SiO_4 (1573 K) fitted with previous work and the ultrasonically measured bulk sound speed (C_o) in shock velocity (U_S)-particle velocity (u_p) space yields the Hugoniot: U_S = 1.58(0.03) u_p + 2.438(0.005) km/s. Sink/float results are in agreement with shock wave and ultrasonic data, consistent with an isothermal K_T = 19.4 GPa and K′ = 5.33 at 1500°C. Shock melting of initially solid Fe_(2)SiO_4 (300 K) confirms that the Grüneisen parameter (γ) of this liquid increases upon compression where γ = γ_o(ρ_(o)/ρ)^q yields a q value of –1.45. Constraints on the liquid fayalite EOS permit the calculation of isentropes for silicate liquids of general composition in the multicomponent system CaO-MgO-Al_(2)O_3-SiO_2-FeO at elevated temperatures and pressures. In our model a whole mantle magma ocean would first crystallize in the mid-lower mantle or at the base of the mantle were it composed of either peridotite or simplified “chondrite” liquid, respectively. In regards to the partial melt hypothesis to explain the occurrence and characteristics of ultra-low velocity zones, neither of these candidate liquids would be dense enough to remain at the core mantle boundary on geologic timescales, but our model defines a compositional range of liquids that would be gravitationally stable. ", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/64925, title ="A New Approach to In-situ K-Ar Geochronology", author = "Hurowitz, J. A. and Farley, K. A.", month = "October", year = "2012", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160301-140249059", revision_no = "11", abstract = "The development of an in-situ geochronology capability for Mars and other planetary surfaces has the potential to fundamentally change our understanding of the evolution of terrestrial bodies in the Solar System. For Mars specifically, many of our most basic scientific questions about the geologic history of the planet require knowledge of the absolute time at which an event or process took place on its surface. For instance, what was the age and rate of early Martian climate change recorded in the mineralogy and morphology of surface lithologies (e.g., [1])? In-situ ages from a few select locations within the globally established stratigraphy of Mars would be transformative, enabling us to place direct chronologic constraints on the timing and rates of impact, volcanic, sedimentary, and aqueous processes on the Martian surface. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/30060, title ="Structure of shock compressed model basaltic glass: Insights from O K-edge X-ray Raman scattering and high-resolution ^(27)Al NMR spectroscopy", author = "Lee, Sung Keun and Park, Sun Young", journal = "Geophysical Research Letters", volume = "39", number = "5", pages = "Art. No. L05306 ", month = "March", year = "2012", doi = "10.1029/2012GL050861 ", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120411-104758286", note = "© 2012 American Geophysical Union. \n\nReceived 9 January 2012; revised 3 February 2012; accepted 7 February 2012; published 3 March 2012. \n\nThis work was supported by the National Research Foundation, Korea to S.K.L. (2007-000-20120) and through subcontract\n675P of NNSA DE-FC88-01NV14049 to O.T.. HPCAT was supported\nby DOE-BES-Materials Science, DOE-NNSA, CDAC, NSF,\nDOD–TACOM, and the W.M. Keck Foundation. The Caltech shock wave\nlab is supported by NSF EAR-1119522. We thank two anonymous\nreviewers for constructive comments.", revision_no = "21", abstract = "The detailed atomic structures of shock compressed basaltic glasses are not well understood. Here, we explore the structures of shock compressed silicate glass with a diopside–anorthite eutectic composition (Di_(64)An_(36)), a common Fe-free model basaltic composition, using oxygen K-edge X-ray Raman scattering and high- resolution ^(27)Al solid-state NMR spectroscopy and report previously unknown details of shock-induced changes in the atomic configurations. A topologically driven densification of the Di_(64)An_(36) glass is indicated by the increase in oxygen K-edge energy for the glass upon shock compression. The first experimental evidence of the increase in the fraction of highly coordinated Al in shock compressed glass is found in the ^(27)Al NMR spectra. This unambiguous evidence of shock-induced changes in Al coordination environments provides atomistic insights into shock compression in basaltic glasses and allows us to microscopically constrain the magnitude of impact events or relevant processes involving natural basalts on Earth and planetary surfaces.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/28920, title ="Does sea level influence mid-ocean ridge magmatism on Milankovitch timescales?", author = "Lund, David C. and Asimow, Paul D.", journal = "Geochemistry Geophysics Geosystems", volume = "12", pages = "Art. No. Q12009", month = "December", year = "2011", issn = "1525‐2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120123-123856074", note = "© 2011 by the American Geophysical Union. Received 10 May 2011; Revised 12 October 2011; Accepted 13 October 2011; Published 13 December 2011. We thank John Maclennan, Donna Blackman, and three anonymous reviewers for their constructive criticism. We would also like to thank Peter Huybers, Marc Spiegelman, and John Southon for comments and suggestions. Funding for this project was in part provided by the University of Michigan (D. Lund).", revision_no = "15", abstract = "Magma production at mid-ocean ridges is driven by seafloor spreading and decompression melting of the upper mantle. In the special case of Iceland, mantle melting may have been amplified by ice sheet retreat during the last deglaciation, yielding anomalously high rates of subaerial volcanism. For the remainder of the global mid-ocean ridge system, the ocean may play an analogous role, with lowering of sea level during glacial maxima producing greater magma flux to ridge crests. Here we show that the mantle decompression rate associated with changes in sea level is a substantial fraction of that from plate spreading. Modeled peaks in magma flux occur after sea level drops rapidly, including the Marine Isotope Stage (MIS) 5/4 and 3/2 transitions. The minimum in simulated flux occurs during the mid-Holocene, due to the rapid sea level rise at the MIS 2/1 boundary. The model results are highly sensitive to melt migration rate; rates of ~1 m/yr produce small signals, while those >5 m/yr yield substantial anomalies. In the latter case, sea level-driven magma flux varies by 15–100% relative to the long-term average, with the largest effect occurring at slow-spreading ridges. We suggest that sedimentary time series of hydrothermal particle flux, oceanic Os isotopic ratio, and oceanic radiocarbon may serve as proxies for magma-flux variations at mid-ocean ridges. Although well-dated records are rare, preliminary data from the Pacific and Atlantic suggest hydrothermal metal flux was elevated during MIS 2 and 4, broadly consistent with our modeling results. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/28581, title ="Analysis of hydrogen in olivine by SIMS: Evaluation of standards and protocol", author = "Mosenfelder, Jed L. and Le Voyer, Marion", journal = "American Mineralogist", volume = "96", number = "11-12", pages = "1725-1741", month = "November", year = "2011", doi = "10.2138/am.2011.3810", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111223-081023439", note = "© 2011 Mineralogical Society of America. \n\nManuscript received February 17, 2011. Manuscript accepted July 5, 2011. Manuscript handled by Florian Heidelbach. \n\nFinancial support for this research was provided by the Gordon and Betty Moore Foundation, the White Rose Foundation, and by NSF grant EAR-0947956 to George Rossman. We thank Erik Hauri, Jeremy Boyce, and Richard Hervig for helpful discussions; Chi Ma for assistance with the electron microprobe and SEM; and Jörg Hermann and an anonymous reviewer for helpful suggestions that improved the manuscript.", revision_no = "20", abstract = "We measured hydrogen concentrations in 12 olivines using secondary ion mass spectrometry (SIMS and NanoSIMS), cross-calibrated against Fourier transform infrared (FTIR) spectroscopy and nuclear reaction analysis (NRA). Five of these samples are routinely used for calibration in other laboratories. We assess the suitability of these olivines as standards based on over 300 SIMS analyses, comprising 22 separate calibrations. Seven olivines with 0–125 ppm H_2O give highly reproducible results; in contrast to previous studies, the data are fit to well-constrained calibration lines with high correlation coefficients (r^2 = 0.98–1). However, four kimberlitic megacrysts with 140–245 ppm H_2O sometimes yield ^(16)O^1H/^(30)Si ratios that have low internal precision and can vary by up to a factor of two even in sequential analyses. A possible cause of this behavior is the presence of sub-microscopic inclusions of hydrous minerals, such as serpentine. In most cases, however, we link the anomalous results to the presence of sub-micrometer to micrometer-scale pores (as small as 100 nm), which we imaged using SEM and NanoSIMS. These pores are interpreted to be fluid inclusions containing liquid H_2O, other volatiles (including fluorine), and/or hydrous phase precipitates. Ionization of the contents of the pores contributes variably to the measured ^(16)O^1H, resulting in analyses with erratic depth profiles and corresponding high uncertainties (up to 16%, 2σ_(mean)). After filtering of these analyses using a simple criterion based on the error predicted by Poisson counting statistics, all the data fit well together. Our results imply that the Bell et al. (2003) calibration can be applied accurately to all olivines with IR bands from ~3400–3700 cm^(−1), without the need for band-specific IR absorption coefficients. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27970, title ="Hydrous, Low-carbon Melting of Garnet Peridotite", author = "Balta, Brian J. and Mosenfelder, Jed L.", journal = "Journal of Petrology", volume = "52", number = "11", pages = "2079-2105", month = "November", year = "2011", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111128-103324923", note = "© 2011 The Author. \nPublished by Oxford University Press.\nReceived June 25, 2010. Accepted July 26, 2011. \nFirst published online: August 25, 2011.\nThis work benefited from many enlightening discussions with Sally Newman, George Rossman, Mark\nHirschmann, Liz Miura, Ma Chi, and Mike Baker. The\nauthors would like to thank Alex Sessions and Magnus\nEek for the use of their Elemental Analyzer, Ed Stolper\nand John Beckett for the use of their 1atm furnaces, and\nClaude Herzberg and George Rossman for supplying\nstarting materials. This paper was significantly improved\nby reviews from Trevor Falloon, Glenn Gaetani, Rajdeep\nDasgupta, and Othmar Müntener. This work was supported by the National Science Foundation Ocean Sciences Marine Geology and Geophysics program, grant numbers OCE-0241716 and OCE-0550216.\n", revision_no = "19", abstract = "The presence of volatile species in the Earth's upper mantle drives the formation of low-degree melts at pressures and temperatures at which volatile-free mantle rocks would be subsolidus. The two most abundant volatile species, given the oxidation state of the Earth's upper mantle, are carbon dioxide and water; each species has a distinct effect on the melting process. We present experimental melting results from 3\u2009GPa and 1375°C on hydrous systems with controlled water contents and rigorously minimized carbon contamination that constrain the independent effects of these volatiles. The hydrous melts in these experiments are in equilibrium with garnet peridotite at pressures reasonable for hydrous melting under mid-ocean ridges. Compared with anhydrous experiments or carbon-rich silicate melting, the addition of water produces a melt with increased SiO_2 content relative to MgO and FeO, tantamount to an increase in the stability of olivine at the solidus relative to the other crystalline phases. We also report a substantial and unexpected change in the composition of clinopyroxene in equilibrium with the melt; the clinopyroxene stability field contracts when water is added to the system, producing clinopyroxenes with higher CaO and lower Al_2O_3 than found at the same pressure without water. The contraction of the clinopyroxene field decreases the bulk partition coefficients of TiO_2, Na_2O, heavy rare earth elements, U, and H_2O, with important implications for hydrous melting of the mantle; for example, initiating hydrous melting deeper in the garnet lherzolite stability field. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27637, title ="Manganese partitioning during hydrous melting of peridotite", author = "Balta, J. Brian and Mosenfelder, Jed L.", journal = "Geochimica et Cosmochimica Acta", volume = "75", number = "20", pages = "5819-5833", month = "October", year = "2011", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111107-075300895", note = "© 2011 Elsevier Ltd. Received 28 June 2010; accepted in revised form 10 November 2010; available online 25 May 2011. Associate editor: Michael Toplis. The authors thank Andrew Matzen and Mike Baker for illuminating discussions regarding the behavior and analysis of MnO in experiments. Associate Editor Michael Toplis, reviewer Claude Herzberg, and an anonymous reviewer helped improve the manuscript. This work was supported by the NSF Ocean Sciences Marine Geology and Geophysics program, Grant Nos. OCE-0241716 and OCE-0550216. ", revision_no = "14", abstract = "Manganese contents and the iron/manganese ratio of igneous rocks have been used as a method of probing the heterogeneity in the Earth’s mantle during melting of peridotite and pyroxenite lithologies. Most previous work has assumed that changes in these parameters require differences in either source lithology or composition based on experiments indicating that manganese is slightly incompatible during melting and that the iron/manganese ratio is fixed by the presence of olivine. However, the presence of volatiles in the mantle drives melting at lower temperatures and with different compositions than in volatile-free systems, and thus the partitioning of Fe and Mn may in fact vary. We have produced silicate liquids in equilibrium with a peridotite assemblage under hydrous conditions at 3 GPa that show that Mn can also be unexpectedly compatible in garnet at 1375 °C and that Mn partitioning between solids and liquids can be strongly affected by temperature and liquid composition. The compatibility of Mn in garnet provides a mechanism for large variations of Mn contents and the Fe/Mn ratio in silicate melts that solely involves melting of mantle peridotite with only small compositional changes. Correlations between Mn variations and other indices indicative of melting in the presence of garnet may provide a means of more completely understanding the role of garnet at high pressures in peridotite melting.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27546, title ="Thermodynamic properties of alloys of gold-74/palladium-26 with variable amounts of iron and the use of Au-Pd-Fe alloys as containers for experimental petrology", author = "Balta, Brian J. and Beckett, John R.", journal = "American Mineralogist", volume = "96", number = "10", pages = "1467-1474", month = "October", year = "2011", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111101-091711413", note = "© 2011 by Mineralogical Society of America. Manuscript received June 25, 2010. Manuscript accepted May 11, 2011.\nManuscript handled by Charles Lesher. The authors thank J.K. Wicks and A.K. Matzen for their help with the 1 atm furnace experiments, and J.H. Jones and T.L. Grove for comments. This work was supported by the NSF Ocean Sciences Marine Geology and Geophysics program, Grant numbers OCE-0241716 and OCE-0550216, and NASA Grant number NNG04GG14G.", revision_no = "14", abstract = "Iron oxide-alloy equilibration experiments were conducted in H_2-CO_2 gas mixtures at 1 atm and 1125–1240 °C using strips of Au_(74)Pd_(26) (wt%) and produced Au-Pd-Fe alloys with 0.03–13 wt% iron. A thermodynamic calibration for the mixing of Au_(74)Pd_(26) with iron using an asymmetric regular solution leads to WG_(-Fe) = –45.0 ± 1.8 kJ/mol and WG_(-AuPd) = +19.5 ± 7.7 kJ/mol (1σ). Internal oxidation of\niron was observed in a reversal experiment, suggesting that oxygen can be transferred across capsule boundaries during high-temperature experiments. This thermodynamic calibration is applicable to a wide range of oxygen fugacities and iron activities relevant to petrological and metallurgical applications at 1 atm and, as previous studies suggest excess volumes in this system are small, it can also be used to predict Fe activities in experiments at elevated pressure (up to 3 GPa). By pre-doping Au-Pd capsules to match Fe activities expected for the sample during an experiment, it is possible to maintain samples with little to no loss of iron. Pre-saturation of the capsule also provides a method for controlling the oxygen fugacity of samples if no formal oxygen buffer is available.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/30026, title ="Shock compression of preheated silicate liquids: Apparent universality of increasing Grüneisen parameter upon compression", author = "Asimow, Paul D.", number = "1426", pages = "887-890", month = "June", year = "2011", isbn = "978-0-7354-1006-0", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120409-073622038", note = "© 2012 American Institute of Physics.\n\nFunding was provided by the US National\nScience Foundation, awards EAR-0855774, EAR-0810116 and EAR-1119522.", revision_no = "14", abstract = "Shock compression experiments achieving ≥ 100 GPa pressures are available for seven silicate liquid compositions in the system CaO-MgO-FeO-Al_2O_3-SiO_2. Especially when liquid states have been sampled along multiple Hugoniots, these data are sufficient to evaluate the dependence of Grüneisen γ on volume in silicate liquids. The increase in γ upon compression in these liquids is a surprising feature, but this behavior is seen consistently in all studied compositions, by multiple experimental techniques and also in ab initio molecular dynamics (MD) simulations. The remarkable observation when comparing all the studied liquids is that the rate of increase of γ upon compression is approximately universal. It can be described by q = (dln γ/dlnV) = -1.5±0.25 in all seven compositions. This places very strong constraints on microscopic models for silicate liquid compression behavior and suggests a general rule for computing isentropes and densities of silicate liquids of arbitrary composition under any conditions likely to occur in a terrestrial mantle or magma ocean.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/21044, title ="Shock compression of liquid silicates to 125 GPa: The anorthite‐diopside join", author = "Ahrens, Thomas J. and Asimow, Paul D.", journal = "Journal of Geophysical Research B", volume = "115", pages = "Art. No. B10209", month = "October", year = "2010", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101129-141006829", note = "© 2010 American Geophysical Union. Received 17 November 2009, revised 8 June 2010, accepted 30 June 2010, published 26 October 2010. This paper has taken many years of sustained\neffort by our irreplaceable technical staff: Michael Long, Eprapodito\nGelle and Russel Oliver. Yongqin Jiao contributed to the very early stages\nand Daoyuan Sun made substantial contributions to the middle stage of the\neffort. Jed Mosenfelder provided the anorthite glass sample and frequent\nadvice. Mark Ghiorso kindly carried out the fits of this data to his EOS formalism\nand shared prepublication results of his work with Frank Spera.\nThis work was supported by the U. S. National Science Foundation through\nawards EAR‐0207934, EAR‐0409785, EAR‐0552009, EAR‐0555685,\nEAR‐0609804 and EAR‐0810116.", revision_no = "19", abstract = "We determined the equation of state (EOS) of three silicate liquid compositions by shock compression of preheated samples up to 127 GPa. Diopside (Di; Ca_2Mg_2SiO_6)\nat 1773 K, anorthite (An; CaAl_2Si_2O_8) at 1923 K and the eutectic composition Di_(64)An_(36) at 1673 K were previously studied by shock compression to 38 GPa. The new data extend the EOS of each composition nearly to the Earth’s core-mantle boundary. The previously reported anomaly at 25 GPa for Di_(64)An_(36) eutectic was not reproduced; rather all data for this composition fit within error a straight line Hugoniot in particle velocity vs. shock velocity. Di also displays a linear Hugoniot consistent with ultrasonic data and a third-order finite strain EOS. The full anorthite data set is complex; we examine a model with a transition between two structural states and a fourth‐order finite strain model\nexcluding two points that may not display relaxed behavior. We also report an experiment on room-temperature solid Di_(64)An_(36) aggregate that clearly demonstrates increase upon compression of the Grüneisen parameter of this liquid, much as experiment and theory have shown for forsterite and enstatite liquids. We construct isentropes and isotherms from our Hugoniots using Mie-Grüneisen thermal pressure and evaluate the model of ideal mixing of volumes. Volume may mix almost linearly at high temperature, but deviates\nstrongly when calculated along an isotherm; it remains difficult to reach a firm conclusion. We compare the densities of liquids to lower mantle solids. Our results suggest that basaltic liquids rich in CaO and Al_2O_3 are notably denser than liquids in the MgO-SiO_2 binary and, subject to uncertainties in the behavior of FeO and in corrections for thermal pressure, such liquids may be the most likely candidates for achieving negative buoyancy in the lowermost mantle.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/22633, title ="Oxygen isotope constraints on the structure and evolution of the Hawaiian plume", author = "Wang, Zhengrong and Eiler, John M.", journal = "American Journal of Science", volume = "310", number = "8", pages = "683-720", month = "October", year = "2010", doi = "10.2475/08.2010.01 ", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110303-110017789", note = "© 2010 American Journal of Science. \n\nZW is grateful for instructive comments from Stanley Hart, Ed Stolper, Mike\nBaker, George Rossman, Donald S. Burnett, Ken Farley, Fred Frey, Shichun Huang,\nIlya Bindeman, Glenn A. Gaetani, Alberto Saal, Nobu Shimizu, Paul Hess, and Yan\nLiang. We also want to thank Dr. Michael Roden, Keith Putirka and an anonymous\nreviewer for their helpful reviews that significantly improve the quality of the paper.", revision_no = "16", abstract = "The oxygen isotope stratigraphy of Ko‘olau volcano, Hawaii, is constructed by analyzing olivine phenocrysts from the KSDP drill core and submarine land-slide deposits. Along with those of subaerial (Makapu‘u) Ko‘olau olivines (Eiler and others, 1996a), they span the full range of the δ^(18)OVSMOW variation previously observed in \"Loa-trend\" Hawaiian volcanoes (Lō‘ihi, Mauna Loa, Hualalai, and Ko‘olau), vary systematically with the stratigraphic position, and correlate with other geochemical properties of their host lavas (Tanaka and others, 2002; Haskins and Garcia, 2004; Huang and Frey, 2005; Salters and others, 2006; Fekiacova and others, 2007). These observations can be explained if the \"Loa-trend\" volcanoes (including Ko‘olau) are constructed of magmas made by mixing peridotite melt with variable proportions of eclogite melt derived from a mafic constituent of the Hawaiian plume having a composition resembling recent mid-ocean-ridge basalts. We present a model of this magma mixing process that simultaneously explains the correlations among oxygen isotopes, major elements, trace elements and radiogenic isotopes. Although a number of models of this kind, differing in several parameters, describe the data equally well, all statistically acceptable models require an \"enriched\" component with a MORB-like HREE pattern and enriched oxygen isotope composition (δ^(18)OVSMOW = 7.8-9.7‰), consistent with this component being an upper crustal (layer 1 or 2) basalt or gabbro with a low-temperature alteration history, possibly containing a small amount of sediment. Abundances of some minor elements—Ni and Ti—are not well described by this model; we show that these shortcomings are derived from the compositional assumption and operational difficulties, that is, TiO_2 content is too high in our assumed eclogite end-member, and the inversion of NiO content in the melt by the olivine addition calculation is imprecise due to the sensitivity of D_(NiO)^(olivine/melt) to the melt composition and to crystallization process. Previous studies have advocated that Hawaiian lavas were derived from partial melts of an olivine-free pyroxenite formed by reaction of eclogite-derived melt with peridotite (for example, Sobolev and others, 2005). Our study shows that the peridotite-derived and eclogite-derived melt-mixing model can explain the geochemistry of Hawaiian lavas as well, including high-Ni Ko‘olau olivines. We find that an olivine-free mantle source for Hawaiian lavas is unnecessary, although melt-rock interaction could be important in modifying melt composition. Inverting for mixing proportions and degree of melting, we estimate that the amount of recycled crust in the Hawaiian plume is <24 weight percent. Comparison of the late shield-stage \"Loa-trend\" (particularly Ko‘olau lavas) and \"Kea-trend\" (particularly Mauna Kea lavas) suggests that the geochemical diversity of Hawaiian lavas is produced by a thermally and chemically-zoned plume.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18734, title ="Advances in Shock Compression of Mantle Materials and Implications", author = "Ahrens, Thomas J. and Mosenfelder, Jed L.", number = "1195", pages = "859-862", month = "December", year = "2009", isbn = "978-0-7354-0732-9", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100618-105854615", note = "© 2010 American Institute of Physics.\nIssue Date: 28 December 2009.", revision_no = "14", abstract = "Hugoniots of lower mantle mineral compositions are sensitive to the conditions where they cross phase boundaries including both polymorphic phase transitions and partial to complete melting. For SiO_2, the Hugoniot of fused silica passes from stishovite to partial melt (73 GPa, 4600 K) whereas the Hugoniot of crystal quartz passes from CaCi_2 structure to partial melt (116 GPa, 4900 K). For Mg_2SiO_4, the forsterite Hugoniot passes from the periclase +MgSiO_3 (perovskite) assemblage to melt before 152 GPa and 4300 K, whereas the wadsleyite Hugoniot transforms first to periclase +MgSiO_3 (post-perovskite) and then melts at 151 GPa and 4160 K. Shock states achieved from crystal enstatite are molten above 160 GPa. High-pressure Grüneisen parameters for molten states of MgSiO_3 and Mg_2SiO_4 increase markedly with compression, going from 0.5 to 1.6 over the 0 to 135 GPa range. This gives rise to a very large (>2000 K) isentropic rise in temperature with depth in thermal models of a primordial deep magma ocean within the Earth. These magma ocean isentropes lead to models that have crystallization initiating at mid-lower mantle depths. Such models are consistent with the suggestion that the present ultra-low velocity zones, at the base of the lowermost mantle, represent a dynamically stable, partially molten remnant of the primordial magma ocean. The new shock melting data for silicates support a model of the primordial magma ocean that is concordant with the Berkeley-Caltech iron core model [1] for the temperature at the center of the Earth.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18743, title ="Shock temperatures of preheated MgO", author = "Fat'yanov, Oleg V. and Asimow, Paul D.", journal = "AIP Conference Proceedings", number = "1195", pages = "855-858", month = "December", year = "2009", issn = "0094-243X", isbn = "978-0-7354-0732-9", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100621-092634935", note = "© 2009 American Institute of Physics.\nWe thank M. Long, E. Gelle, and R. Oliver for\nvaluable technical assistance. Funding was\nprovided by the U.S. NSF, grant EAR-0810116.", revision_no = "20", abstract = "Shock temperature measurements via optical pyrometry are being conducted on <100> single-crystal MgO preheated before compression to 1905–1924 K. Planar shocks were generated by impacting hot Mo(driver plate)-MgO targets with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 6.6 km/s. Quasi-brightness temperature was measured with 2–3% uncertainty by a 6-channel optical pyrometer with 3 ns time resolution, over 500–900 nm spectral range. A high-power, coiled irradiance standard lamp was adopted for spectral radiance calibration accurate to 5%. In our experiments, shock pressure in MgO ranged from 102 to 203 GPa and the corresponding temperature varied from 3.78 to 6.53 kK. For the same particle velocity, preheated MgO Hugoniot has about 3% lower shock velocity than the room temperature Hugoniot. Although model shock temperatures calculated for the solid phase exceeded our measurements by ~5 times the uncertainty, there was no clear evidence of MgO melting, up to the highest compression achieved.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/17189, title ="Iron isotopes may reveal the redox conditions of mantle melting from Archean to Present", author = "Dauphas, Nicolas and Craddock, Paul R.", journal = "Earth and Planetary Science Letters", volume = "288", number = "1-2", pages = "255-267", month = "October", year = "2009", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100114-145831911", note = "© 2009 Elsevier B.V.\nReceived 3 June 2009; \nrevised 14 September 2009; \naccepted 16 September 2009. \nEditor: R.W. Carlson. \nAvailable online 28 October 2009. Discussions with J.M. Eiler, M. Roskosz, E.M. Stolper, K.A. Farley, F.-Z.\nTeng, R. Yokochi, V.B. Polyakov and A. Pourmand, careful reviews by\nF. Poitrasson and E.A. Schauble, as well as comments by editor R.W.\nCarlson, were greatly appreciated. This work was supported by a\nPackard fellowship, the France Chicago Center, a Moore Distinguished\nScholarship at the California Institute of Technology, and NASA through\ngrants NNG06GG75G and NNX09AG59G to N.D. S.S. Sorensen, Smithsonian\nInstitution, generously provided some boninite and island arc\nbasalt samples.\n", revision_no = "21", abstract = "High-precision Fe isotopic data for 104 samples, including modern and ancient (≥ 3.7 Ga) subduction-related magmas and mantle peridotites, are presented. These data demonstrate that mid-ocean ridge and oceanic-island basalts (MORBs and OIBs) have on average small, but distinctly (~+ 0.06‰) higher ^(56)Fe/^(54)Fe ratios than both modern and Eoarchean boninites and many island arc basalts (IABs) that are interpreted to form by large degrees of flux melting of depleted mantle sources. Additionally boninites and many IABs have iron isotopic compositions similar to chondrites, fertile mantle peridotites, Eoarchean mantle peridotites, and basalts from Mars and Vesta. The observed variations are best explained by the bulk silicate Earth having a near-chondritic iron isotopic composition, with ~ + 0.3‰ equilibrium isotope fractionation between Fe^(3+) and Fe^(2+) and preferential extraction of isotopically heavier, incompatible Fe^(3+) during mantle melting to form oceanic crust (as represented by MORBs and OIBs). A quantitative model that relates the iron isotopic composition of basaltic magmas to the degree of partial melting, Fe^(3+)/Fe^(2+) ratio, and buffering capacity of the mantle is presented. The concept that redox conditions may influence iron isotopic fractionation during melting provides a new approach for understanding the redox conditions of magma genesis on early Earth and Mars. Experimental and theoretical work is required to establish iron isotopic fractionation as an oxybarometer of mantle melting.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/16465, title ="Fluid source-based modeling of melt initiation within the subduction zone mantle wedge: Implications for geochemical trends in arc lavas", author = "Hebert, Laura Baker and Asimow, Paul D.", journal = "Chemical Geology", volume = "266", number = "3-4", pages = "297-310", month = "August", year = "2009", doi = "10.1016/j.chemgeo.2009.06.017", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20091022-152025976", note = "© 2009 Elsevier. \n\nReceived 30 August 2008; revised 15 April 2009; accepted 15 June 2009. Editor: D.B. Dingwell. Available online 25 June 2009. \n\nhe authors would like to thank C. Hall and M. Gurnis for collaboration in the GyPSM-S modeling effort. We additionally thank editors Paul Hall, Stephanie Escrig and D.B. Dingwell. Very helpful reviews were provided by James Conder and an anonymous reviewer. Support was provided through the Tectonics Observatory by the Gordon and Betty Moore Foundation.", revision_no = "27", abstract = "The GyPSM-S (Geodynamic and Petrological Synthesis Model for Subduction) scheme couples a petrological model with a 2-D thermal and variable viscosity flow model to describe and compare fundamental processes occurring within the subduction mantle wedge, including the development of a low-viscosity channel (LVC) (Hebert et al., 2009, Earth and Planetary Science Letters, v. 278, p. 243–256). Here we supplement the basic coupled model result with more sophisticated treatments of trace element partitioning in the fluid phase and melt transport regimes. We investigate the influences of slab fluid source lithology and fluid transport mechanisms on melt geochemistry, the implications of mantle source depletion related to fluid fluxing, and potential melt migration processes. This study describes two model cases that can be compared to geochemical datasets for the Izu–Bonin intra-oceanic subduction system and the Central Costa Rican part of the Central American arc. We find that there is a progression of geochemical characteristics described in studies of cross-arc and along-arc lavas that can be approximated assuming (i) limited fluid–rock interaction within the mantle wedge and (ii) that melt migration preserves the spatial distinction among melts initiated in different areas of the wedge. Specifically, volcanic front lavas have significant contributions from shallower slab fluid sources, and rear-arc lavas have significant contributions from deeper slab fluid sources. Evidence for limited fluid–rock interaction could imply either a rapid fluid transport mechanism or a fluid-dominated trace element budget within the LVC. Although we do not include a back-arc in these models, interpretations of the results lead to several potential mechanisms to explain hydrous inputs to back-arc source regions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/15640, title ="Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes", author = "Tschauner, Oliver and Kostandova, Natalya", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "106", number = "33", pages = "13691-13695", month = "August", year = "2009", doi = "10.1073/pnas.0905751106", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090908-083701874", note = "Copyright ©2009 by the National Academy of Sciences. \n\nContributed by Thomas J. Ahrens, June 17, 2009 (received for review June 20, 2008). Published online before print August 10, 2009, doi: 10.1073/pnas.0905751106 \n\nWe thank M. Long, E. Gelle, R. Oliver, E. Miura, and G. Rossman for experimental and analytical support. This work was supported by National Science Foundation Grant 0552010, National Nuclear Security Administration Cooperative Agreement DOE-FC88-01NV14049, and National Aeronautics and Space Administration/Goddard Grants NNG04GP57G and NNG04GI07G. N.K. was supported by the California Institute of Technology Summer Undergraduate Research Fellowships program and Mr. and Mrs. Robert E. Anderson. The High Pressure Collaborative Access Team facility was supported by the Department of Energy-Basic Energy Sciences, Department of Energy-National Nuclear Security Administration, National Science Foundation, Department of Defense-Army Tank-Automotive and Armaments Command, and the W. M. Keck Foundation. The U2A beamline is supported by the Consortium for Materials Properties Research in Earth Sciences under National Science Foundation Cooperative Agreement 06-49658, Department of Energy Grant DE-FC52-08NA28554. Advanced Photon Source, Advanced Light Source, and National Synchrotron Light Source are supported by the Department of Energy-Basic Energy Sciences under Contracts W-31-109-Eng-38, DE-AC02–05CH11231, and DE AC02-98CH10886, respectively. Field emission scanning electron microscopy, EBSD, and EMP analyses were carried out at the California Institute of Technology Geological and Planetary Sciences Division Analytical Facility, which is supported in part by National Science Foundation Grant EAR-0318518 and the National Science Foundation Materials Research Science and Engineering Center Program under Grant DMR-00800065. \n\nAuthor contributions: O.T., P.D.A., and T.J.A. designed research; O.T., P.D.A., N.K., C.M., S.S., Z.L., S.F., and N.T. performed research; O.T., P.D.A., and N.K. contributed new reagents/analytic tools; O.T., P.D.A., and N.K. analyzed data; and O.T., P.D.A., N.K., and T.J.A. wrote the paper. \n\nThe authors declare no conflict of interest.", revision_no = "22", abstract = "We observed micrometer-sized grains of wadsleyite, a high-pressure phase of (Mg,Fe)_2SiO_4, in the recovery products of a shock experiment. We infer these grains crystallized from shock-generated melt over a time interval of <1 μs, the maximum time over which our experiment reached and sustained pressure sufficient to stabilize this phase. This rapid crystal growth rate (≈1 m/s) suggests that, contrary to the conclusions of previous studies of the occurrence of high-pressure phases in shock-melt veins in strongly shocked meteorites, the growth of high-pressure phases from the melt during shock events is not diffusion-controlled. Another process, such as microturbulent transport, must be active in the crystal growth process. This result implies that the times necessary to crystallize the high-pressure phases in shocked meteorites may correspond to shock pressure durations achieved on impacts between objects 1–5 m in diameter and not, as previously inferred, ≈1–5 km in diameter. These results may also provide another pathway for syntheses, via shock recovery, of some high-value, high-pressure phases. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/15126, title ="Partial melting of deeply subducted continental crust and the formation of quartzofeldspathic polyphase inclusions in the Sulu UHP eclogites", author = "Zeng, Ling Sen and Liang, Feng Hua", journal = "Chinese Science Bulletin", volume = "54", number = "15", pages = "2580-2594", month = "August", year = "2009", issn = "1001-6538", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090817-144819738", note = "© 2009 Springer. \n\nReceived March 31, 2009; accepted May 14, 2009; published online June. \n\nSupported by the National Natural Science Foundation of China (Grant No. 40673027), Outlay Research Fund of Chinese Academy of Geological Sciences (Grant No.20071120101125). \n\nWe thank Prof. Zheng Yongfei, Ye Kai, Yang Jianjun, Liu Fulai, and John Eiler for discussion in preparing the manuscript. We also thank Prof. Yang Jianjun and other reviewers for providing thoughtful comments that enable us to clarify our interpretations.", revision_no = "15", abstract = "Two types of quartzofeldspathic inclusions hosted by omphacite and garnet were identified in the Sulu UHP eclogites. The first consists of albite, quartz, and various amounts of K-feldspar. In contrast, the second consists predominantly of K-feldspar and quartz without any albite. The presence of quartzofeldspathic inclusions within the UHP mafic eclogites indicates that partial melting occurred in deeply subducted continental crust via mica dehydration melting reactions at an early stage of rapid exhumation. Such a melting event generated hydrous Na-K-Al-Si melts. These melts infiltrated into the mafic eclogite and were captured by recrystallizing garnet or omphacite, which together followed by dehydration and crystallization to form feldspar-bearing polyphase inclusions. Formation of silicate melts within the deeply subducted continental slab not only provides an excellent medium to transport both mobile (LILE) and immobile (HFSE) elements over a large distance, but also induces effective changes in the physical properties of the UHP slab. This process could be a major factor that enhances rapid exhumation of a deeply subducted continental slab.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/15661, title ="Simultaneous aluminum, silicon, and sodium coordination changes in 6 GPa sodium aluminosilicate glasses", author = "Kelsey, Kimberly E. and Stebbins, Jonathan F.", journal = "American Mineralogist", volume = "94", number = "8-9", pages = "1205-1215", month = "August", year = "2009", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090908-083706628", note = "© 2009 Mineralogical Society of America. \n\nManuscript received December 19, 2008. Manuscript accepted April 24, 2009. \n\nWe are grateful to Bob Jones for microprobe analyses, to NSF for funding under grants numbered EAR-0408410 (support for Kelsey and Stebbins) and OCE-0550216 (support for Mosenfelder and Asimow), and to J. Puglisi and C. Liu for access to the 18.8 T NMR spectrometer at the Stanford Magnetic Resonance Laboratory.", revision_no = "14", abstract = "We present the first direct observation of high-coordinated Si and Al occurring together in a series of high-pressure sodium aluminosilicate glasses, quenched from melts at 6 GPa. Using ^(29)Si MAS NMR, we observe that a small amount of Al does not have a significant effect on the amount of ^VSi or ^(VI)Si generated, but that larger Al concentrations lead to a gradual decrease in both these species. ^(27)Al MAS NMR spectra show that samples with small amounts of Al have extremely high mean Al coordination values of up to 5.49, but that larger Al concentrations cause a gradual decrease in both ^VAl and ^(VI)Al. Although mean Al and Si coordination numbers both decrease with increasing Al contents, the weighted combined (Al+Si) coordination number increases. Silicon and Al resonances shift in frequency with increasing pressure or changing Al concentration, indicating additional structural changes, including compression of network bond angles. Increases in the ^(23)Na isotropic chemical shifts indicate decreases in the mean Na-O bond lengths with increasing pressure, which are more dramatic at higher Al contents. Recovered glass densities are about 10 to 15% greater than those of similar ambient pressure samples. However, the density increases due to the combined coordination changes of Al and Si are estimated to total only about 1 to 2%, and are roughly constant with composition despite the large effects of Al content on the individual coordinations of the two cations. Thus, effects of other structural changes must be significant to the overall densification. Apparent equilibrium constants for reactions involving the generation of high-coordinated species show systematic behavior, which suggests an internal consistency to the observed Si and Al coordination number shifts. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/15611, title ="Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results\n", author = "Kelsey, Kimberly E. and Stebbins, Jonathan F.", journal = "Geochimica et Cosmochimica Acta", volume = "73", number = "13", pages = "3914-3933", month = "July", year = "2009", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090904-104213330", note = "Copyright © 2009 Elsevier. \n\nReceived 18 September 2008; accepted 30 March 2009. Associate editor: Michael Toplis. Available online 14 April 2009. \n\nWe are grateful to Bob Jones for microprobe analyses, to Namjun Kim for help with the ^(45)Sc NMR, to Sarah Gaudio (University of California, Davis) for assistance with density measurements, to François Farges (Muséum National d’Histoire Naturelle, Paris) for useful discussion about the La XAFS, and to J. Puglisi and C. Liu for access to the 18.8 T NMR spectrometer at the Stanford Magnetic Resonance Laboratory. We also thank John Bargar, Joe Rogers, and the SSRL staff for continuing beamline support at the Stanford Synchrotron Radiation Laboratory. SSRL is a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences, and is also supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Center for Research Resources, Biomedical Technology Program. We acknowledge the support of the NSF for funding under Grant Nos. EAR-0408410 (Stebbins), CHE-0431425 (Brown), and OCE-0550216 (Asimow), and Associate Editor Mike Toplis, as well as S.K. Lee and two anonymous reviewers for helpful comments on the original version of this paper.", revision_no = "16", abstract = "We examined aluminosilicate glasses containing a variety of network modifying to intermediate cations (Li, La, Sc, and Fe), quenched from melts at 1 atm to 8 GPa, to further investigate the role of cation field strength in Al coordination changes and densification. ^(27)Al Nuclear Magnetic Resonance Spectroscopy (NMR) reveals that the mean Al coordination increases with increasing pressure in the Li-containing glasses, which can be explained by a linear dependence of fractional change in Al coordination number on cation field strengths in similar K-, Na-, and Ca-containing aluminosilicate glasses (K < Na < Li < Ca). Measured recovered densities follow a similar linear trend. In contrast, the La-containing glasses have significantly lower mean Al coordination numbers at given pressures than the cation field strength of La and glass density would predict. La L_3 X-ray absorption fine structure (XAFS) spectroscopy results indicate a significant increase with pressure in average La–O bond distances, suggesting that La and Al may be “competing” for higher coordinated sites and hence that both play a significant role in the densification of these glasses, especially in the lower pressure range. However, in Na aluminosilicate glasses with small amounts of Sc, ^(45)Sc NMR reveals only modest Sc coordination changes, which do not seem to significantly affect the mean Al coordination values. For a Li aluminosilicate glass, ^(17)O MAS and multiple quantum magic angle spinning (3QMAS) NMR data are consistent with generation of more highly coordinated Al at the expense of non-bridging oxygen (NBO), whereas La aluminosilicate glasses have roughly constant O environments, even up to 8 GPa. Finally, we demonstrate that useful ^(23)Na and ^(27)Al MAS NMR spectra can be collected for Ca–Na aluminosilicate glasses containing up to 5 wt.% Fe oxide. We discuss the types of structural changes that may accompany density increases with pressure and how these structural changes are affected by the presence of different cations.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/14769, title ="Origins of chemical diversity of back-arc basin basalts: a segment-scale study of the Eastern Lau Spreading Center", author = "Bézos, Antoine and Escrig, Stéphane", journal = "Journal of Geophysical Research B", volume = "114", pages = "B06212", month = "June", year = "2009", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090803-114642416", note = "© 2009 American Geophysical Union.\nReceived 10 July 2008; revised 24 January 2009; accepted 6 April 2009; published 30 June 2009.\nThis work benefited from the very thorough reviews by Terry Plank and an anonymous reviewer and from discussions with Steve Parman and Paul Hall. We would like to thank Sue Woods for assistance on ICP-MS at Harvard University and Nilanjan Chatterjee and Steve Parman for assistance on electron Microprobe at the MIT Electron Microprobe Facility. This work was supported by the National Science Foundation grant OCE-0242618.\nIndex Terms: 3001 Marine Geology and Geophysics: Back-arc basin processes; 1037 Geochemistry: Magma genesis and partial melting (3619); 1065 Geochemistry: Major and trace element geochemistry; 1009 Geochemistry: Geochemical modeling (3610, 8410); 3610 Mineralogy and Petrology: Geochemical modeling (1009, 8410).\n\n", revision_no = "18", abstract = "We report major, trace, and volatile element data on basaltic glasses from the northernmost segment of the Eastern Lau Spreading Center (ELSC1) in the Lau back-arc basin to further test and constrain models of back-arc volcanism. The zero-age samples come from 47 precisely collected stations from an 85 km length spreading center. The chemical data covary similarly to other back-arc systems but with tighter correlations and well-developed spatial systematics. We confirm a correlation between volatile content and apparent extent of melting of the mantle source but also show that the data cannot be reproduced by the model of isobaric addition of water that has been broadly applied to back-arc basins. The new data also confirm that there is no relationship between mantle temperature and the wet melting productivity. Two distinct magmatic provinces can be identified along the ELSC1 axis, a southern province influenced by a “wet component” with strong affinities to arc volcanism and a northern province influenced by a “damp component” intermediate between enriched mid-ocean ridge basalts (E-MORB) and arc basalts. High–field strength elements and rare earth elements are all mobilized to some extent by the wet component, and the detailed composition of this component is determined. It differs in significant ways from the Mariana component reported by E. Stolper and S. Newman (1994), particularly by having lower abundances of most elements relative to H_(2)O. The differences can be explained if the slab temperature is higher for the Mariana and the source from which the fluid is derived is more enriched. The ELSC1 damp component is best explained by mixing between the wet component and an E-MORB-like component. We propose that mixing between water-rich fluids and low-degree silicate melts occurs at depth in the subduction zone to generate the chemical diversity of the ELSC1 subduction components. These modified sources then rise independently to the surface and melt, and these melts mix with melts of the background mantle from the ridge melting regime to generate the linear data arrays characteristic of back-arc basalts. The major and trace element framework for ELSC1, combined with different slab temperatures and compositions for difference convergent margins, may be able to be applied to other back-arc basins around the globe. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33715, title ="Melt-rock interactions during the early stages of rapid exhumation of a deeply subducted continental slab", author = "Zeng, Lingsen and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "73", number = "13", pages = "A1500", month = "June", year = "2009", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-134955865", note = "© 2009 Pergamon-Elsevier Science Ltd.\nSupported by the Natural Science Foundation of China\n(Grant no. 40673027) and CAGS outlay research project.", revision_no = "15", abstract = "Polyphase inclusions of K-feldspar + quartz + sphene were\nfounded in both omphacite and garnet from the Sulu ultra-high\npressure eclogites. These inclusions have clear cut boundaries\nwith their host and display irregular internal textures. Each of\nthe fifteen identified inclusions is unique in its shape and\nmodal contents of K-feldspar (Kf; 18-85%), quartz (Qtz; 8-\n78%) and sphene (Sph; 11-38%). Reconstructed bulk\ncompositions have SiO_2 ranging from 56.6 to 91.0 wt%, Al_2O_3\nfrom 3.4 to 15.4 wt%, K_2O from 3.0 to 14.2 wt%, CaO from\n0.4 to 10.8 wt%, and TiO_2 from 0.5 to 12.5 wt%. We interpret\nthese inclusions as products of reaction between K-rich\nhaplogranitic melt and quartz (coesite) aggregates, generating\na range of compositions according to the degree of progress of\nthis reaction. The hybrid melts subsequently migrated into a\nmafic assemblage and were trapped during dynamic\nrecrystallization of the major eclogite minerals. This\nhypothesis implies that either a melt rich in K and Si or a\nsupercritical fluid was present during the subduction and\nexhumation of the Sulu UHP slab, at a stage preceding the end\nof eclogite facies conditions. The fluid phase must furthermore\nhave been sufficiently mobile to pass from its host lithology\nthrough both silica-saturated and mafic regions of the\ncontinental slab. Although the initial fluid may have\ntransported only fluid-mobile (LILE) elements, evidently the\nfinal hybrid melt carried enough Ti to crystallize sphene and\nhence transported also fluid-immobile (HFSE) elements\nduring the exhumation of the continental slab. Furthermore, if\nthe mobile phase began as a hydrous fluid, by the time the\nhybrid melt or cumulate minerals from the hybrid melt were\ntrapped, water activity had reached low enough values to\navoid the precipitation of any hydrous minerals.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33906, title ="Probing the conditions of mantle melting with iron isotopes", author = "Dauphas, N. and Craddock, P. R.", journal = "Geochimica et Cosmochimica Acta", volume = "73", number = "13", pages = "A266-A266", month = "June", year = "2009", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-110328624", note = "© 2009 Pergamon-Elsevier Science Ltd.\n", revision_no = "17", abstract = "While extraterrestrial basalts have near-chondritic iron\nisotopic compositions (~0 ‰), mid-ocean ridge and ocean\nisland basalts have heavy δ^(56)Fe (~+0.1 ‰ relative to IRMM-\n014) [e.g., 1]. This was interpreted to reflect kinetic isotope\nfractionation associated with vaporization during the Moon-forming\nimpact [2] or equilibrium fractionation at core-mantle\nboundary conditions [3]. A more mundane interpretation is\nthat Fe isotopes are fractionated during partial melting [4].\nIndeed, fertile mantle peridotites define a δ^(56)Fe value of\n0.02±0.03., indistinguishable from chondrites [4]. In\naddition, measurable isotopic fractionation between olivine\nand melt was recently documented in a natural example of\nmagmatic differentiation [5]. Whether Eoarchean magmas had δ^(56)Fe similar to phanerozoic MORBs-OIBs is presently\nunknown. Dauphas et al. [6] suggested that such magmas\ncould have had δ^(56)Fe closer to chondritic but analytical\nprecision was insufficient to reach a definitive conclusion. We\nreport high precision isotopic analyses of Fe [7] in chondrites\nand mafic igneous rocks. Several Eoarchean island arc basalts\nand boninites have Fe isotopic compositions similar to mantle\nperidotites. A quantitative model is presented that can explain\nFe isotopic variations measured in mantle-derived magmas.\nWhile Fe isotopes may not be very useful for tracing processes\nof planetary formation, they provide invaluable information on\nthe conditions of magma genesis through time.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/14978, title ="Advances in high-pressure mineral physics: from the deep mantle to the core \n", author = "Ohtani, Eiji and Andrault, Denis", journal = "Physics of the Earth and Planetary Interiors", volume = "174", number = "1-4", pages = "1-2", month = "May", year = "2009", issn = "0031-9201", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090812-090452180", note = "© 2009 Elsevier.\nAvailable online 21 March 2009.\n", revision_no = "15", abstract = "Mineral physics studies provide basic information on physical,\nchemical, thermodynamic and transport properties of constituents\nof the Earth’s interior. This information, combined with other geophysical\nobservations, helps constrain the structure and dynamics\nof the Earth. This Physics of the Earth and Planetary Interiors special\nissue is a collection of the experimental, computational and theoretical\nresearch and review papers relating to recent “Advances in\nMineral Physics: from the Deep Mantle to the Core” and written by\nsome of theworld’s leading scientists in this field. This special issue\nis a proceedings volume of the 7th High Pressure Mineral Physics\nSeminar (HPMPS-7) held on May 8–12, 2007 at Matsushima, Japan.\nThe High Pressure Mineral Physics Seminar series was established\nin 1976 by scientists mainly fromthe United States and Japan. Since\nthen,meetings have been organized approximately every 4–5 years.\nHPMPS-7was the second suchmeeting attended by scientists from\nthe United States, Japan, and Europe. An important activity of this\nmeeting series is the publishing of proceedings that, because of\nthe wide scope and high level of the contributions, serve as essential\nreviews of the scientific and technical progress in the field of\nhigh-pressure mineral physics. Previous volumes were published\nby American Geophysical Union, in 1987, 1992 and 1998, as Geophysical\nMonographs (volumes 39, 67 and 101, respectively) and\nin 2003 as a special issue of Physics of the Earth and Planetary\nInteriors.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/14475, title ="Shock compression of preheated molybdenum to 300 GPa", author = "Sun, Daoyuan and Ahrens, Thomas J.", journal = "Physics of the Earth and Planetary Interiors", volume = "174", number = "1-4", pages = "302-308", month = "May", year = "2009", doi = "10.1016/j.pepi.2008.08.004", issn = "0031-9201", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090701-113819858", note = "© 2008 Elsevier B.V.\nReceived 26 September 2007; revised 14 July 2008; accepted 4 August 2008. Available online 15 August 2008. \nThe expert technical assistance of Michael Long, Eprapodito Gelle, and Russel Oliver is appreciated, as always. This work was supported by the U.S. National Science Foundation through grant EAR-0609804. PDA also gratefully acknowledges travel support from NSF for attending the HPMPS-7 conference in Matsushima, Japan.", revision_no = "16", abstract = "Shock compression experiments on samples at elevated initial temperature provide a test of the Mie-Grüneisen method of predicting off-principal Hugoniot states. Pure molybdenum, preheated to 1673 K, was shocked to peak pressures up to 300 GPa, double the compression range previously studied for this material at elevated temperature. The data lie strictly below the cold Hugoniot of Mo in shock velocity vs. particle velocity space, with some downward curvature. Previous approximations and extrapolations from lower-compression data fail to match these results, but the data are well fit by a Mie-Grüneisen correction to the cold Hugoniot. However, the data are insufficiently precise and the phases obtained in the shock experiments too uncertain to discriminate among different functional forms of the density dependence of the Grüneisen parameter.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/13904, title ="Emergence of a low-viscosity channel in subduction zones through the coupling of mantle flow and thermodynamics", author = "Hebert, Laura Baker and Antoshechkina, Paula", journal = "Earth and Planetary Science Letters", volume = "278", number = "3-4", pages = "243-256", month = "February", year = "2009", doi = "10.1016/j.epsl.2008.12.013", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090409-112119432", note = "© 2008 Elsevier B.V. \n\nReceived 15 August 2008. Received in revised form 4 December 2008. Accepted 5 December 2008. Available online 25 January 2009. \n\nEditor: R.D. van der Hilst. \n\nThe authors would like to especially thank Chad Hall for his substantial early work on code and concept development. This work\nbenefited from helpful discussion with V. Manea, M. Chen, B. Hacker, and S. Kidder and from very constructive comments by two\nanonymous reviewers and editors C. Jaupart and R. van der Hilst.\nSupport provided through the Caltech Tectonics Observatory by the\nGordon and Betty Moore Foundation. All calculations carried out on\nthe Caltech Geosciences Supercomputer Facility partially supported by NSF EAR-0521699.", revision_no = "24", abstract = "We use a petrological model (pHMELTS), coupled with a 2D thermal and variable viscosity flow model (ConMan), to describe and compare fundamental processes occurring within subduction zones. We study the thermal state and phase equilibria of the subducting oceanic slab and adjacent mantle wedge and constrain fluid flux. Using a Lagrangian particle distribution to perform thousands of thermodynamically equilibrated calculations, the chemical state of the domain is continuously updated. Compositionally and thermally dependent buoyancy and viscosity terms provide a consistent linkage between the effect of water addition to and flow within the mantle wedge. We present seven model cases that span normal ranges in subducting slab age, convergence velocity, and slab dip angle. In all models, the coupling between chemistry and dynamics results in behavior previously unresolved, including the development of a continuous, slab-adjacent low-viscosity channel (LVC) defined by hydrous mineral stability and higher concentrations of water in nominally anhydrous minerals (NAM). As the LVC evolves to fluid saturation, slab-derived components are able to migrate vertically upwards to the water-saturated solidus, forming a melting region that bounds the top of the LVC. The LVC develops due to fluid ingress into the mantle wedge from the dehydrating slab, and can be responsible for slab decoupling, large-scale changes in the wedge flow field, and a mechanism by which hydrated slab-adjacent mantle material can be transported to the deep mantle. Varying model parameters indicates that slab age and slab dip angle exert primary control over LVC shape and thickness, due to changing fluid release patterns within the slab. Younger slabs tend to have thinner, more uniform LVCs, while older slabs tend to have a thinner LVC at shallow depths with a large increase in LVC thickness at ~100 km depth. Slab convergence velocity appears to have a secondary role in controlling LVC shape.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/13552, title ="The MgSiO_3 system at high pressure: Thermodynamic properties of perovskite, postperovskite, and melt from global inversion of shock and static compression data", author = "Mosenfelder, Jed L. and Frost, Daniel J.", journal = "Journal of Geophysical Research B", volume = "114", pages = "B01203", month = "January", year = "2009", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:MOSjgrb09", note = "© 2009 American Geophysical Union.\nReceived 26 June 2008; accepted 3 November 2008; published 14 January 2009.\nFunding for this work was provided by the Bayerisches Geoinstitut and by National Science Foundation grant EAR-\n0207934. We thank H. Fischer for technical support of multianvil experiments in Germany; M. Long, P. Gelle, and R. Oliver for support with the shock wave experiments at Caltech; B. Balta for obtaining microprobe analyses; and T. Schneider for advice on statistics.", revision_no = "28", abstract = "We present new equation-of-state (EoS) data acquired by shock loading to pressures up to 245 GPa on both low-density samples (MgSiO_3 glass) and high-density, polycrystalline aggregates (MgSiO_3 perovskite + majorite). The latter samples were synthesized using a large-volume press. Modeling indicates that these materials transform to perovskite, postperovskite, and/or melt with increasing pressure on their Hugoniots. We fit our results together with existing P-V-T data from dynamic and static compression experiments to constrain the thermal EoS for the three phases, all of which are of fundamental importance to the dynamics of the lower mantle. The EoS for perovskite and postperovskite are well described with third-order Birch-Murnaghan isentropes, offset with a Mie-Grüneisen-Debye formulation for thermal pressure. The addition of shock data helps to distinguish among discrepant static studies of perovskite, and for postperovskite, constrain a value of K' significantly larger than 4. For the melt, we define for the first time a single EoS that fits experimental data from ambient pressure to 230 GPa; the best fit requires a fourth-order isentrope. We also provide a new EoS for Mg_2SiO_4 liquid, calculated in a similar manner. The Grüneisen parameters of the solid phases decrease with pressure, whereas those of the melts increase, consistent with previous shock wave experiments as well as molecular dynamics simulations. We discuss implications of our modeling for thermal expansion in the lower mantle, stabilization of ultra-low-velocity zones associated with melting at the core-mantle boundary, and crystallization of a terrestrial magma ocean.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/12012, title ="Petrology of some oceanic island basalts: PRIMELT2.XLS software for primary magma calculation", author = "Herzberg, C. and Asimow, Paul D.", journal = "Geochemistry, Geophysics, Geosystems", volume = "9", number = "9", pages = "2008GC002057", month = "September", year = "2008", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:HERggg08", note = "© 2008 American Geophysical Union. \n\nReceived: 10 April 2008; Revised: 2 July 2008; Accepted: 15 July 2008; Published: 18 September 2008. \n\nKaj Hoernle and Mike Rhodes are thanked for discussions. We are grateful to John Longhi and Cin-Ty Lee for thoughtful reviews. P.D.A. is supported by the NSF through grant OCE-0550216. \n\nAuxiliary material for this article contains a Microsoft Excel workbook called PRIMELT2.XLS in which the primary magma calculations described in this paper are implemented. \n\nAdditional file information is provided in the readme.txt.\n\nThe primary magma calculations described in this paper are implemented in this Microsoft Excel workbook, PRIMELT2.XLS. Please note that this workbook uses Visual Basic for Applications (VBA) macros for several of the iterative calculations. As such, it is incompatible with Microsoft Office 2008 for Macintosh, which does not support VBA macros. There may be other incompatibility issues that we are not aware of, but it has been tested on Microsoft Windows XP 2002 using Microsoft Office 2004 and on MacOS 10.4 and 10.5 using Microsoft Office 2004. A user guide is provided in Appendix A2 on implementation of PRIMELT2.XLS.", revision_no = "26", abstract = "PRIMELT2.XLS software is introduced for calculating primary magma composition and mantle potential temperature (TP) from an observed lava composition. It is an upgrade over a previous version in that it includes garnet peridotite melting and it detects complexities that can lead to overestimates in TP by >100°C. These are variations in source lithology, source volatile content, source oxidation state, and clinopyroxene fractionation. Nevertheless, application of PRIMELT2.XLS to lavas from a wide range of oceanic islands reveals no evidence that volatile-enrichment and source fertility are sufficient to produce them. All are associated with thermal anomalies, and this appears to be a prerequisite for their formation. For the ocean islands considered in this work, TP maxima are typically ~1450–1500°C in the Atlantic and 1500–1600°C in the Pacific, substantially greater than ~1350°C for ambient mantle. Lavas from the Galápagos Islands and Hawaii record in their geochemistry high TP maxima and large ranges in both TP and melt fraction over short horizontal distances, a result that is predicted by the mantle plume model.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/11873, title ="A model for rutile saturation in silicate melts with applications to eclogite partial melting in subduction zones and mantle plumes", author = "Gaetani, Glenn A. and Stolper, Edward M.", journal = "Earth and Planetary Science Letters", volume = "272", number = "3-4", pages = "720-729", month = "August", year = "2008", doi = "10.1016/j.epsl.2008.06.002", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:GAEepsl08", note = "© 2008 Elsevier. \n\nReceived 27 July 2007; revised 4 June 2008; accepted 5 June 2008. Available online 11 June 2008. \n\nConstructive reviews by S. Foley and R. Lange led to significant improvements to the paper. We are grateful to FJ Ryerson for supplying unpublished data. GG is grateful to Z. Wang for helpful discussions, and M. Jackson for pointing out the importance of understanding rutile saturation in mantle plumes. This work was supported by NSF through grants EAR-9725461, EAR-0096340, EAR-0112013 and EAR-0239513.", revision_no = "17", abstract = "This experimental study examines the solubility of rutile in silicate melts and presents a model for rutile saturation as a function of temperature, pressure and melt composition. Rutile saturation experiments were carried out in the system SiO2–TiO2–Al2O3–MgO–CaO–Na2O–K2O at 1 bar to 35 kbar and 1150 to 1450 °C on model rhyodacite (~ 69 wt.% SiO2) and haplobasalt (~ 54 wt.% SiO2) base melt compositions. At rutile saturation, the concentration of TiO2 in the model rhyodacite base melt increases at 1 bar from 3.27 ± 0.03 wt.% at 1150 °C to 13.88 ± 0.04 wt.% at 1450 °C. At 1350 °C it decreases from 8.89 ± 0.08 wt.% at 1 bar to 2.06 ± 0.13 wt.% at 35 kbar. Rutile solubility is significantly higher in the haplobasalt base melt at a given pressure and temperature. The concentration of TiO2 in rutile-saturated haplobasalt increases at 1 bar from 20.9 ± 0.3 wt.% at 1300 °C to 39.0 ± 0.3 wt.% at 1450 °C. At 1350 °C it decreases from 25.8 ± 0.3 wt.% at 1 bar to 15.67 ± 0.16 wt.% at 15 kbar. Results from these experiments were combined with data from the literature to formulate a model for rutile saturation in silicate melts. Application of this model to partial melting of MORB-type eclogite indicates that beneath volcanic arcs low-degree, hydrous partial melts of rutile-bearing subducted oceanic crust contain only not, vert, similar 600 ppm TiO2. Therefore, rutile will remain as a residual phase in the eclogite and the amount of TiO2 that will be transferred to the mantle wedge will be small because so little TiO2 is dissolved in the melt. Partial melting of recycled oceanic crust in an upwelling mantle plume can exhaust rutile from the residual solid at moderate degrees of partial melting (~ 22%). The retention of rutile in subducted oceanic lithosphere during dehydration and/or partial melting, combined with exhaustion of rutile during partial melting of eclogite in mantle plumes suggests that HFSE enrichments in recycled crust that were established during subduction may be detectible in OIB.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33913, title ="H_2O and Cl in basalts from Lau back-arc basin", author = "Michael, P. J. and Bézos, A.", journal = "Geochimica et Cosmochimica Acta", volume = "72", number = "12", pages = "A624-A624", month = "July", year = "2008", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-133428491", note = "© 2008 Pergamon-Elsevier Science Ltd.", revision_no = "15", abstract = "The subduction influence (fluid mobile elements) in\nbasalts along the back arc Eastern Lau Spreading Center\n(ELSC) increases in several sharp gradients as the distance to\nthe Tofua volcanic arc diminishes from 100 km in the north\n(19°S) to 40 km in the south (23°S). The six tectonic segments\nof ELSC display mixing relationships in trace element and\nisotopic ratios in which one end member is a subduction\ncomponent that is distinctive for each segment. Basalts from\nthe three well-sampled northern segments (ELSC-1, -2, and -3,\nfrom 19.2-20.7°S) are best for the study of volatiles because\nmost did not lose H_2O by degassing, and because they display\na wide range of H_2O/ element values on a local scale: from\nMORB-like to much higher values.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33709, title ="Thermodynamic phase relations of the MgO-FeO-SiO_2 system in the lower mantle", author = "Wolf, A. S. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "72", number = "12", pages = "A1031", month = "July", year = "2008", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-131132987", note = "© 2008 Pergamon-Elsevier Science Ltd.", revision_no = "15", abstract = "The perovskite (Pv) to post-perovskite (PPv) phase\ntransition at pressures near the Earth’s core-mantle boundary\n(CMB) is currently the favored candidate for explaining most, if not all, of the peculiarities of the D’’ layer (~200 km region\nabove core) [1, 2]. The intense interest in this layer is\nmotivated by its role in determining the boundary condition on\nthe bottom of the convecting mantle, thereby greatly affecting\nmantle dynamics. The post-perovskite phase boundary in pure\nMgSiO_3 is fairly well known, but the experimental and\ncalculated results on the partitioning of Fe among the stable\ncoexisting phases and its influence on the transition pressure\nare currently contradictory [3-5].", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33712, title ="Petrogenesis of Ultramafic Rocks from the Ultrahigh-pressure Metamorphic Kimi Complex in Eastern Rhodope (NE Greece)", author = "Baziotis, I. and Mposkos, E.", journal = "Journal of Petrology", volume = "49", number = "5", pages = "885-909", month = "May", year = "2008", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-132255566", note = "© 2007 Oxford University Press.\n\nReceived January 25, 2007; accepted February 13, 2008.\nFirst published online: March 24, 2008.\nI.B. and E.M. were financially supported by the Project\n‘Pythagoras I’, co-funded by the European Social Fund\n(75%) and National Resources (25%), and by the National Technical University of Athens for the Special Research Project ‘Protagoras’. P.D.A. was financially supported\nby the US National Science Foundation through grant EAR-0239513. Critical and constructive reviews by\nO. Müntener, E. Hellebrand and an anonymous reviewer\nhelped us to improve the manuscript and are gratefully\nacknowledged. We want to express our sincere thanks to\nM. Wilson for her helpful remarks and extraordinarily\npatient editorial handling.\n", revision_no = "19", abstract = "Widespread bodies of garnet–spinel metaperidotites with pyroxenitic layers occur in the ultrahigh-pressure metamorphic Kimi Complex. In this study we address the origin of such peridotite–pyroxenite associations in the context of polybaric melting regimes. We conduct a detailed geochemical investigation of major and trace element relations and compare them with a range of major element modelling scenarios. With increasing bulk-rock MgO content, the garnet–spinel metaperidotites exhibit decreasing CaO, Al_(2)O_3, TiO_2, and Na_(2)O along with increasing Ni and a gradually increasing Zr/Zr* anomaly, consistent with an origin as residues after variable degrees of melt extraction. The major element modelling further suggests a polybaric adiabatic decompression melting regime beginning at high to ultrahigh pressure, with an intermediate character between pure batch and fractional melting and a mean extent of melting of 9–11%. The pyroxenites exhibit major element compositions that cannot be reproduced by experimental or calculated melts of peridotite. Moreover, the Kimi pyroxenites have highly variable Ni and Sc contents and a wide range of Mg-number (0·76–0·89), inconsistent with an origin as frozen melts or the products of melt–peridotite interaction. However, both the major element systematics and the observed rare earth element patterns, with both convex and concave shapes, can be explained by an origin as clinopyroxene-rich, high-pressure cumulates involving garnet and/or Cr-spinel. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33876, title ="Cation order/disorder behavior and crystal chemistry of pyrope-grossular garnets: An ^(17)O 3QMAS and ^(27)Al MAS NMR spectroscopic study", author = "Kelsey, Kimberly E. and Stebbins, Jonathan F.", journal = "American Mineralogist", volume = "93", number = "1", pages = "134-143", month = "January", year = "2008", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-151541763", note = "© 2008 American Mineralogist. Manuscript received February 26, 2007. Manuscript accepted September 12, 2007. Manuscript handled by Michael Fechtelkord. We are grateful to Tom Sisson, Ben Hankins, and the USGS, Menlo Park for the use of piston cylinder apparatus, to NSF for continued funding under grant number EAR 0408410, and to J. Puglisi and C. Liu for access to the 18.8 T NMR spectrometer at the Stanford Magnetic Resonance Laboratory. We thank Sung Keun Lee, Robtera Oberti, and an anonymous reviewer for helpful comments on an early version of this paper.", revision_no = "14", abstract = "The thermodynamic mixing properties of the pyrope-grossular solid solution show large deviations from ideality, which could be partly related to Ca-Mg order/disorder. In this study, synthetic pyrope-grossular garnets with X_(Mg) = 1.00, 0.91, 0.75, 0.50, 0.24, 0.10, and 0.00 are observed using ^(17)O 3QMAS, ^(27)Al MAS, and ^(29)Si MAS NMR to examine Ca-Mg order/disorder behavior and crystal chemical variations. The ^(17)O 3QMAS NMR spectra show four distinct resonances, assigned to four different local oxygen coordination environments; two resemble end-member garnets (oxygen bonded to two Mg or two Ca) and two are intermediate (oxygen bonded to one Ca and one Mg), indicating that there are two distinct bond distances for the Mg-O and/or Ca-O bonds through the entire solid solution. Noticeable changes in the NMR peak position for two of the oxygen sites suggest that as X_(Mg) increases, the longer Ca-O bond shortens. The relative areas for the different oxygen sites are close to those predicted using a model of random Ca/Mg mixing. The maximum allowed reduction in configurational entropy from first neighbor Ca-Mg ordering is insignificant relative to other configurational entropy reductions and excess vibrational entropy. These conclusions are not inconsistent with published theoretical calculations suggesting some Ca-Mg ordering that involves correlations beyond the first neighbor, as suggested by published theoretical calculations. Even at 18.8 Tesla, the ^(27)Al MAS NMR spectra do not resolve different local Al sites with varying combinations of X cation neighbors. The ^(29)Si MAS NMR spectra have resonance broadening, probably caused by the addition of 0.15 wt% Fe_2O_3 in the synthetic samples, and are consistent with published results suggesting a small degree of Ca-Mg ordering that is not reflected in the ^(17)O NMR spectra.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33475, title ="Insights into mantle melting from graphical analysis of one-component systems", author = "Stolper, Edward M. and Asimow, Paul D.", journal = "American Journal of Science", volume = "307", number = "8", pages = "1051-1139", month = "October", year = "2007", doi = "10.2475/08.2007.01", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120823-103455957", note = "© 2007 American Journal of Science. \n\nThis manuscript is an outgrowth of various lectures and classes given by the authors over several years, including especially the Ingerson lecture of the Geochemical\nSociety (1996), a series of Bateman lectures given at Yale (2005), and the Crosby lectures at MIT (2006) by EMS. We are particularly grateful to Marc Hirschmann for his many contributions to the material presented here over the past decade; to Paula Smith for her more recent help and advice; to Peter Reiners for suggesting that we put it together into a manuscript for publication in this journal; and to reviewers John Longhi and S. A. Morse for their helpful suggestions. Finally, EMS wishes to acknowledge Professor J.B. Thompson’s influence on his thinking about many of the issues presented in this paper and particularly, as pointed out by S. A. Morse, Professor Thompson’s “emphasis on the felicitous choice of thermodynamic variables in petrology,\nand in choosing the variable to fit the problem” and his use of P-S diagrams in his two remarkable Harvard courses, “Phase equilibrium in mineral systems” and “Metamorphism”.", revision_no = "17", abstract = "Decompression melting can be approximated as an isentropic (that is, reversible adiabatic) process. In such a process, specific entropy (S) and pressure (P) are the independent variables and equilibrium is achieved when the specific enthalpy (H) of the system reaches a minimum. We present a largely graphical analysis of decompression melting in one-component systems based on phase equilibria in H-P-S space. Although mantle sources contain more than one component, use of one-component model systems provides insights into several aspects of mantle melting that can be generalized to more complete and complex systems (for example, batch vs. fractional fusion; the influence of pressure-dependent solid-solid reactions on melting; melting of multilithologic mixtures such as peridotite plus eclogite; advection of heat and melting by rising magmas) and places these insights into the visualizable framework of simple phase diagrams.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33702, title ="Experimental study of radium partitioning between anorthite and melt at 1 atm", author = "Miller, Sarah A. and Burnett, Donald S.", journal = "American Mineralogist", volume = "92", number = "8-9", pages = "1535-1538", month = "August", year = "2007", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-094514028", note = "© 2007 Mineralogical Society of America.\n\nManuscript received: March 19, 2007; manuscript accepted: May 10, 2007; manuscript handled by Bryan Chakoumakos.\n\nThe authors thank Haick Issaian and Andre Jefferson of the Caltech Safety Office for their time and expertise in assisting with safe handling of materials. NORIT Americas, Inc. generously donated activated charcoal for radon containment. Constructive reviews by Kari Cooper and Ken Sims improved the manuscript. This work was supported by NASA grants NAG5-11640 and NNG05GH79G to D. Burnett and NNH04AB47I to I. Hutcheon, NSF EAR-0239513 to P. Asimow\nand LLNL Laboratory Directed Research and Development funding. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract\nW-7405-ENG-48.", revision_no = "15", abstract = "We present the first experimental radium mineral/melt partitioning data, specifically between anorthite and a CMAS melt at atmospheric pressure. ^(226)Ra disequilibria are an important chronometer of recent magmatic activity. Ion microprobe measurement of coexisting anorthite and glass phases produces a molar D_Ra = 0.040 ± 0.006 and D_(Ra)/D_(Ba) = 0.24 ± 0.05 at 1400 °C. Our results indicate that lattice strain partitioning models fit the divalent (Ca, Sr, Ba, Ra) partition coefficient data of this study well, supporting previous work on crustal melting and magma chamber dynamics that has relied on such models to approximate radium partitioning behavior in the absence of experimentally determined values. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33716, title ="Heterogeneity in mid-ocean ridge sources", author = "Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "71", number = "15", pages = "A40", month = "August", year = "2007", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-135650241", note = "© 2007 Pergamon-Elsevier Science Ltd.", revision_no = "13", abstract = "This talk will review some theoretical considerations\nconcerning the melting of heterogeneous sources and the\nimplications for interpretation of melt inclusion data,\nparticularly olivine-hosted inclusions from mid-ocean ridge\nenvironments. We have apparently adequate models that\nassume a locally or globally homogenous source and can\nexplain major and trace element chemistry of basalts and\ncorrelations with physical variables like melt flux and axial\ndepth. Such models are the basis of the consensus view of the\naverage thermal and compositional state of the upper mantle\nand the range of their variability. However, a variety of data\n(most notably from melt inclusion diversity within samples\nand suites) and lines of reasoning (such as the need for\nrecycling to maintain fertility of the source) require that\nheterogeneity exists within particular melting regimes as well\nas among them. We can classify heterogeneity by scale. There\nis some small scale (perhaps ~10 cm) below which the source\nmelts as if it were effectively homogeneous and some large\nscale (perhaps ~ 1 km) above which the source components\ncan be treated as chemically and thermally independent and\ntheir melts simply mixed; these scales may be different for\ndifferent elements and lithologies. The challenge is to develop\ntools that predict behavior at intermediate scales where\nincomplete thermal and/or chemical interaction occur and\nhence standard mixing theory is confounded by complex\nfeedbacks between composition and melting behavior and\nbetween melting and equilibration. Additional challenges\ncenter on the kinetics of interactions during melt migration\nthrough heterogeneous media.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33717, title ="Magmatism and the evolution of the Earth's interior", author = "Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "71", number = "15", pages = "A40", month = "August", year = "2007", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-140143504", note = "© 2007 Pergamon-Elsevier Science Ltd.", revision_no = "14", abstract = "The flow of liquids relative to solids or other liquids is the\nonly efficient mechanism for obtaining physical separation of\nchemical components of an initially homogenous material at\nhigh pressure. Hence the history of differentiation of the\nEarth’s interior is essentially the history of magmatic\nphenomena: core formation involving molten metal, formation\nand freezing of a silicate magma ocean, and ongoing partial\nmelting of silicate solids. In early history much of this activity\ntook place at very high pressure, in the lower mantle\n(plausibly, silicate magmatic activity continues today at the\ncore-mantle boundary). In order to define possible\nevolutionary paths of the young Earth and to learn what\nevidence might remain today of such early processes we must\nbuild well-constrained models of igneous processes at\nappropriate pressures, temperatures, and compositions. This\nremains difficult because experimental study of lower mantle\nigneous petrology lies mostly beyond the pressure capability\nof multi-anvil devices and beyond the size and homogeneity\ncapability of diamond anvil cells. We must rely on indirect\ntools: construction of phase diagrams and thermodynamic\nmodels from thermochemical and equation of state data\ncontributed by mineral physics and the emerging field of high-pressure\nmelt physics. There are roles in this enterprise for\nquantum and molecular dynamics computation, shock wave\nexperiments, and a variety of in situ applications of\nsynchrotron radiation. Once the major element phase\nequilibria are well-defined, then it is appropriate to turn to\ntrace elements and the determination of partition coefficients\nat appropriate pressure, temperature, and major element\ncompositions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33851, title ="Thermodynamic properties of Mg_2SiO_4 liquid at ultra-high\npressures from shock measurements to 200 GPa on forsterite and wadsleyite", author = "Mosenfelder, Jed L. and Ahrens, Thomas J.", journal = "Journal of Geophysical Research B", volume = "112", number = "B6", pages = "Art. No. B06208", month = "June", year = "2007", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-095738686", note = "© 2007 American Geophysical Union. Received 24 February 2006; revised 22 November 2006; accepted 1 March 2007; published 30 June 2007. This work was supported by NSF grants EAR-0207934, OCE-0241716, and OCE-0550216. We thank P. Gelle, M. Long, C. McCaughey, and R. Oliver for their expert technical support.\nDaoyuan Sun kindly shared his results on fitting the equation of state of MgO. The manuscript was improved by reviews from Carl Agee and an anonymous referee. Contribution no. 9155, Division of Geological and Planetary Sciences, California Institute of Technology.", revision_no = "13", abstract = "Polycrystalline samples of Mg_2SiO_4 forsterite and wadsleyite were synthesized and then dynamically loaded to pressures of 39–200 GPa. Differences in initial density and internal energy between these two phases lead to distinct Hugoniots, each characterized by multiple phase regimes. Transformation to the high-pressure phase assemblage MgO + MgSiO_3 perovksite is complete by 100 GPa for forsterite starting material but incomplete for wadsleyite. The datum for wadsleyite shocked to 136 GPa, however, is consistent with the assemblage MgO + MgSiO_3 post-perovksite. Marked increases in density along the Hugoniots of both phases between ∼130 and 150 GPa are inconsistent with any known solid-solid phase transformation in the Mg_2SiO_4 system but can be explained by melting. Density increases upon melting are consistent with a similar density increase observed in the MgSiO_3 system. This implies that melts with compositions over the entire Mg/Si range likely for the mantle would be negatively or neutrally buoyant at conditions close to the core-mantle boundary, supporting the partial melt hypothesis to explain the occurrence of ultra-low velocity zones at the base of the mantle. From the energetic difference between the high-pressure segments of the two Hugoniots, we estimate a Grüneisen parameter (γ) of 2.6 ± 0.35 for Mg_2SiO_4-liquid between 150 and 200 GPa. Comparison to low-pressure data and fitting of the absolute pressures along the melt Hugoniots both require that γ for the melt increases with increasing density. Similar behavior was recently predicted in MgSiO_3 liquid via molecular dynamics simulations. This result changes estimates of the temperature profile, and hence the dynamics, of a deep terrestrial magma ocean. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/7596, title ="Temperatures in ambient mantle and plumes: Constraints from basalts, picrites, and komatiites", author = "Herzberg, C. and Asimow, Paul D.", journal = "Geochemistry, Geophysics, Geosystems", volume = "8", number = "2", pages = "2006GC001390", month = "February", year = "2007", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:HERggg07", note = "© 2007 American Geophysical Union. \n\nReceived: 16 June 2006; Revised: 10 October 2006; Accepted: 13 November 2006; Published: 13 February 2007. \n\nWe are very grateful to Don Anderson, Fred Frey, Dave Green, Marc Hirschmann, Charles Langmuir, Keith Putirka, Mike Rhodes, and three anonymous reviewers for critical reviews. We also thank Michael Baker for sharing experimental information and Francis Albarède for numerous discussions. \n\nAuxiliary software calculates primary magma composition using melt fraction F as a constraint as discussed in section A1 of the main text.", revision_no = "9", abstract = "Several methods have been developed to assess the thermal state of the mantle below oceanic ridges, islands, and plateaus, on the basis of the petrology and geochemistry of erupted lavas. One leads to the conclusion that mantle potential temperature (i.e., TP) of ambient mantle below oceanic ridges is 1430°C, the same as Hawaii. Another has ridges with a large range in ambient mantle potential temperature (i.e., TP = 1300–1570°C), comparable in some cases to hot spots (Klein and Langmuir, 1987; Langmuir et al., 1992). A third has uniformly low temperatures for ambient mantle below ridges, ∼1300°C, with localized 250°C anomalies associated with mantle plumes. All methods involve assumptions and uncertainties that we critically evaluate. A new evaluation is made of parental magma compositions that would crystallize olivines with the maximum forsterite contents observed in lava flows. These are generally in good agreement with primary magma compositions calculated using the mass balance method of Herzberg and O'Hara (2002), and differences reflect the well-known effects of fractional crystallization. Results of primary magma compositions we obtain for mid-ocean ridge basalts and various oceanic islands and plateaus generally favor the third type of model but with ambient mantle potential temperatures in the range 1280–1400°C and thermal anomalies that can be 200–300°C above this background. Our results are consistent with the plume model.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33774, title ="Grain boundary partitioning of Ar and He", author = "Baxter, Ethan F. and Farley, Kenneth A.", journal = "Geochimica et Cosmochimica Acta", volume = "71", number = "2", pages = "434-451", month = "January", year = "2007", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-112949050", note = "© 2006 Elsevier Inc.\nReceived 5 July 2005; accepted in revised form 12 September 2006.\nThis study was conducted at Caltech. Manuscript preparation\nwas conducted while EFB was at Boston University.\nWe Jed Mosenfelder, John Beckett and Mike Baker for help with the experiments. We thank Pete Burnard for\nassistance with the noble gas analysis. We thank Carol\nGarland for TEM preparation and analysis. Steve Reese\nof the OSU Reactor Facility was helpful in accommodating\nour irradiations. We thank Lauren Cooper and Jennifer\nWade for assistance in thin section observation. Ed Stolper\nprovided the starting material and access to his labs. We\nthank Bruce Watson, Takeo Hiraga, and Terry Plank for\nvaluable discussions at various stages of the project. Support from a Caltech Postdoctoral Fellowship to EFB and\nNSF Grants EAR-0125784 (to PDA and KAF) and EAR-0337527 (to EFB) is gratefully acknowledged.\nAssociate Editor: Jun-ichi Matsuda\nSupplementary data associated with this article can be\nfound, in the online version, at doi:10.1016/j.gca.2006.09.011.", revision_no = "21", abstract = "An experimental procedure has been developed that permits measurement of the partitioning of Ar and He between crystal interiors and the intergranular medium (ITM) that surrounds them in synthetic melt-free polycrystalline diopside aggregates. ^(37)Ar and ^(4)He are introduced into the samples via neutron irradiation. As samples are crystallized under sub-solidus conditions from a pure diopside glass in a piston cylinder apparatus, noble gases diffusively equilibrate between the evolving crystal and intergranular reservoirs. After equilibration, ITM Ar and He is distinguished from that incorporated within the crystals by means of step heating analysis. An apparent equilibrium state (i.e., constant partitioning) is reached after about 20 h in the 1450 °C experiments. Data for longer durations show a systematic trend of decreasing ITM Ar (and He) with decreasing grain boundary (GB) interfacial area as would be predicted for partitioning\ncontrolled by the network of planar grain boundaries (as opposed to ITM gases distributed in discrete micro-bubbles or melt).\nThese data yield values of GB-area-normalized partitioning, K¯^(Ar)_(ITM), with units of (Ar/m^3 of solid)/(Ar/m^2 of GB) of 6.8 x 10^3 – 2.4 x 104 m^(-1). Combined petrographic microscope, SEM, and limited TEM observation showed no evidence that a residual glass phase or grain boundary micro-bubbles dominated the ITM, though they may represent minor components. If a nominal GB thickness (δ) is assumed, and if the density of crystals and the grain boundaries are assumed equal, then a true grain boundary partition coefficient (K^(Ar)_(GB) = X^(Ar)_(crystals)/X^(Ar)_(GB) may be determined. For reasonable values of δ, K^(Ar)_(GB) is at least an order of magnitude lower than the Ar partition coefficient between diopside and melt. Helium partitioning data provide a less robust constraint with K¯^(He)_(ITM) between 4 x 10^3 and 4 x 10^4 cm^(-1), similar to the Ar partitioning data. These data suggest that an ITM consisting of nominally melt free, bubble free, tight grain boundaries can constitute a significant but not infinite reservoir, and therefore bulk transport pathway, for noble gases in fine grained portions of the crust and mantle where aqueous or melt fluids are non-wetting and of very low abundance (i.e., <0.1% fluid). Heterogeneities in grain size within dry equilibrated systems will correspond to significant differences in bulk rock noble gas content.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33736, title ="Recovery of stishovite-structure at ambient conditions out of shock-generated amorphous silica", author = "Tschauner, Oliver and Luo, Sheng-Nian", journal = "American Mineralogist", volume = "91", number = "11-12", pages = "1857-1862", month = "November", year = "2006", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-160334838", note = "© 2006 Mineralogical Society of America.\n\nManuscript Received June 20, 2005; manuscript Accepted May 30, 2006.\n\nThis work was supported under the NNSA Cooperative Agreement DEFC88-01NV14049 and under NASA PGG Grant NNG04G107G and Contribution no. 9144, Division of Geological and Planetary Sciences, California Institute of\nTechnology. We thank V. Prakapenka, T. Sharp, and R. Jones for their very helpful comments. We thank M. Long and P. Gelle for support in performing the shock experiment and M. Somayazulu for assistance in the synchrotron diffraction experiment.\nUse of the HPCAT facility was supported by DOE-BES, DOE-NNSA, NSF, DOD-TACOM, and the W.M. Keck Foundation. APS is supported by DOE-BES under contract no. W-31-109-Eng-38.", revision_no = "14", abstract = "We show that bulk amorphous silica recovered from shock-wave experiments on quartz to 57 GPa is not a true glass but rather keeps a large degree of long-range structural information that can be recovered by static cold recompression to 13 GPa. At this pressure, shock-retrieved silica assumes the structure of crystalline stishovite. A minor amount of material recovers the structure of a recently discovered new silica polymorph.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33772, title ="Determination of melt influence on divalent element partitioning between anorthite and CMAS melts", author = "Miller, Sarah A. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "70", number = "16", pages = "4258-4274", month = "August", year = "2006", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-112239557", note = "© 2006 Elsevier Inc.\nReceived 12 January 2006; accepted in revised form 16 June 2006.\nWe thank Ma Chi and Julie Paque for electron microprobe\nassistance, as well as Ian Hutcheon and Doug Phinney\nfor help with ion microprobe analyses that allowed us\nto select our analytical course of action in this study. The\nmanuscript benefited from the dedicated reviews of Alexandre\nCorgne and an anonymous reviewer. This work was supported by NASA grants NAG5-11640 and NNG05GH79G to D. Burnett and NSF EAR-0239513 to P. Asimow.\nAssociate editor: F.J. Ryerson", revision_no = "13", abstract = "We propose a theory for crystal-melt trace element partitioning that considers the energetic consequences of crystal-lattice strain, of multi-component major-element silicate liquid mixing, and of trace-element activity coefficients in melts. We demonstrate application of the theory using newly determined partition coefficients for Ca, Mg, Sr, and Ba between pure anorthite and seven CMAS liquid compositions at 1330 °C and 1 atm. By selecting a range of melt compositions in equilibrium with a common crystal composition at equal liquidus temperature and pressure, we have isolated the contribution of melt composition to divalent trace element partitioning in this simple system. The partitioning data are fit to Onuma curves with parameterizations that can be thermodynamically rationalized in terms of the melt major element activity product (a_(Al_2O_3))(a_(SiO_2_)^2 and lattice strain theory modeling. Residuals between observed partition coefficients and the lattice strain plus major oxide melt activity model are then attributed to non-ideality of trace constituents in the liquids. The activity coefficients of the trace species in the melt are found to vary systematically with composition. Accounting for the major and trace element thermodynamics in the melt allows a good fit in which the parameters of the crystal-lattice strain model are independent of melt composition.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33905, title ="Elemental budget and rheology of the oceanic lithosphere", author = "Workman, R. K. and Boettcher, M.", journal = "Geochimica et Cosmochimica Acta", volume = "70", number = "18", pages = "A708-A708", month = "August", year = "2006", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-105418649", note = "© 2006 Published by Elsevier Ltd.\n", revision_no = "15", abstract = "The compositions of the uppermost parts of subducting oceanic plates (sediments and altered crust) are relatively well known. However, the largest part of the downgoing slab, the lithospheric mantle (up to ∼10 times the thickness of the oceanic crust), is not well defined. By virtue of its size and refractory nature, this may be the subducted material with the longest lifespan within the convecting mantle; also, ancient recycled lithosphere may be a source reservoir to modern ocean island volcanism. We present results constraining the chemical compositions of the entirety of subducting tectonic plates, and discuss consequences of variations in lithospheric composition (especially water) for the rheology of subducted plates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33718, title ="Heterogeneity in mid-ocean ridge sources", author = "Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "70", number = "18", pages = "A23", month = "August", year = "2006", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-140449069", note = "© 2006 Pergamon-Elsevier Science Ltd.", revision_no = "15", abstract = "Understanding of decompression melting of homogeneous\nperidotite sources beneath mid-ocean ridges has reached a reasonably\nmature state. One can construct apparently adequate models\nthat relate source composition, including volatile contents, and\npotential temperature to major and trace element chemistry of\nthe aggregate primary liquid and to correlations with physical\nvariables like melt flux and axial depth. Such models are the basis\nof the consensus view of the average thermal and compositional\nstate of the upper mantle and the range of their variability.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33760, title ="Hydrogen incorporation in olivine from 2–12 GPa", author = "Mosenfelder, Jed L. and Deligne, Natalia I.", journal = "American Mineralogist", volume = "91", number = "2-3", pages = "285-294", month = "February", year = "2006", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-102043379", note = "© 2006 Mineralogical Society of America.\n\nManuscript received March 11, 2005; manuscript accepted September 20, 2005; manuscript handled by George Lager.\n\nFinancial support for this investigation was provided by NSF grants OCE-0095294 and OCE-0241716 to P.D.A. and EAR-0337816 to G.R.R. We thank Shun Karato for donation of the synthetic forsterite crystal and Mike Baker for donation\nof olivines and pyroxenes from Kilbourne Hole. Bruce Watson gave expert advice and encouragement on encapsulation techniques. Chi Ma and Elizabeth Miura are thanked for their assistance with electron microprobe and infrared analyses, respectively. Finally, we thank Eugen Libowitzky, Hans Keppler, and an anonymous referee for constructive reviews that improved the manuscript.", revision_no = "15", abstract = "We performed new experiments on incorporation of hydrogen in olivine at high pressures (2–12 GPa) and temperatures (1000–1300°C). OH concentrations were calculated using the Bell et al. (2003) calibration applied to principal-axis infrared absorption spectra synthesized from polarized measurements on randomly oriented grains. Starting materials for the experiments included both fi ne-grained powders and larger single crystals. Hydrogen was incorporated during grain growth in the former case and by volume diffusion in the latter. The spectra of Fe-bearing olivines exhibit similar structure regardless of the starting material, and are dominated by bands in the wavenumber range from about 3500 to 3650 cm^(–1). We do not observe bands at 3525 and 3573 cm^(–1), which are predominant in many natural olivines as well as olivines annealed in experiments at lower pressures, and are attributed to humite-related defects. Furthermore, bands between 3300 and 3400 cm^(–1), attributed to high silica activity or high oxygen fugacity, are weak or non-existent. Our measurements indicate that OH solubility in Fe-bearing olivine is 2.5–4 times higher than that measured by Kohlstedt et al. (1996). Although this is largely due to the use of a new calibration in our study, correction of previous values is not straightforward. In the pure Mg-system, in contrast to Fe-bearing olivine, order-of-magnitude apparent differences in OH solubility can be obtained using different experimental procedures. This raises questions about attainment of equilibrium in experimental studies of hydrogen incorporation in nominally anhydrous minerals, particularly when crystals are grown from a hydrous melt.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33700, title ="Quantitative polarized infrared analysis of trace OH in populations of randomly oriented mineral grains", author = "Stein, Leo C. and Mosenfelder, Jed L.", journal = "American Mineralogist", volume = "91", number = "2-3", pages = "278-284", month = "February", year = "2006", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-094432919", note = "© 2006 Mineralogical Society of America.\n\nManuscript Received March 9, 2005; manuscript Accepted September 11, 2005.\n\nThis work was supported by the National Science Foundation through grant OCE-0241716 to P.D.A. and EAR-0337816 to G.R.R. and by the Caltech SURF program. Thanks to Scott Sitzman of HKL technology for EBSD advice. The manuscript was improved by comments from Eugen Libowitzky, an anonymous reviewer, and associate editor Alison Pawley. ", revision_no = "17", abstract = "Use of infrared spectroscopy as an accurate, quantitative method to measure concentrations of hydrous species in minerals requires consideration of the interactions of anisotropic crystals with infrared light. Ensuring that contributions are identified from species at all orientations in the crystal requires combining three measurements, taken with the electric field polarized along three mutually perpendicular directions. This is typically accomplished by determining the orientation of a crystal in advance, and then sectioning it perpendicular to its principal axes. In many instances, however, natural or experimental samples are not suitable for such handling. Here we demonstrate a method that instead uses at least three randomly sectioned grains, considered to be multiple samples of a homogeneous population. We explain the theory whereby: (1) the orientations of the polarization vectors of measurements taken on these grains are determined by comparison to oriented standards of the same mineral, and (2) the principal-axis spectra of the sample are synthesized from the randomly oriented spectra. By comparison to complementary electron backscatter diffraction (EBSD) data, we demonstrate that determination of orientations using the silicate overtone bands in Fourier-Transform infrared (FTIR) spectra is accurate and precise, with typical angular errors of 6°. We show that this precision is sufficient for the synthetic principal-axis spectra to be essentially indistinguishable from X-ray oriented standard spectra. We demonstrate the application of this technique to determining the OH concentrations in a population of hydrated olivine grains recovered from a high-pressure, high-temperature multi-anvil experiment. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91367, title ="Asimow, Jahren, and Randerson receive 2005 James B. Macelwane Medal", author = "Eiler, John and Asimow, Paul D.", journal = "Eos", volume = "87", number = "4", pages = "40-41", month = "January", year = "2006", doi = "10.1029/2006eo040005", issn = "0096-3941", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181130-105900662", note = "© 2006 American Geophysical Union.", revision_no = "8", abstract = "It is my great pleasure to present my friend and colleague, Paul Asimow, recipient of one of this year's three James B. Macelwane Medals. Paul is a petrologist interested in the origins and evolution of basaltic magmas, and he is being recognized for a series of profoundly insightful papers on the energetics of decompression melting and how it controls the compositions of the oceanic crust and upper mantle.\n\nThe significance of what Paul has done comes from the simplicity of the question that first inspired him: How should we describe the way the mantle melts as it upwells during convection? The importance of the problem is obvious; this is how the Earth makes most of its crust, and so it is the starting point for most of geology But does it sound like something we already understand? Wasn't I taught this as an undergraduate? Paul's first and perhaps most important contribution was to recognize, as a second‐year graduate student working with Ed Stolper [California Institute of Technology (Caltech),Pasadena],that the explanation of mantle melting we were telling each other was a Rube Goldberg device masquerading as physical theory.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/38340, title ="Hydrogen Incorporation in Natural Mantle Olivines", author = "Mosenfelder, Jed L. and Sharp, Thomas G.", number = "168", pages = "45-56", month = "January", year = "2006", isbn = "9780875904337", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130508-075922683", note = "© 2006 by the American Geophysical Union.\nPublished Online: 19 Mar. 2013.\nFinancial support for this work was provided\nby NSF grants OCE-0095294 and OCE-0241716 to PDA,\nEAR-0337816 to GRR, and EAR-0208419 to TGS. Several of the\nBuell Park samples came from the thesis collection repository of\nDavid Bell at Caltech. Doug Smith graciously provided samples,\nenlightening discussion and encouragement. Erik Hauri provided\na preprint and went beyond the call of duty discussing it. We also\nthank Maarten Broekmans, Bradley Hacker, Stephen Mackwell,\nGordon Medaris, Michael Roden, and Michael Terry for helpful\ndiscussions and information about localities. Chi Ma assisted with\nelectron microprobe analyses. Thorough reviews by Andrew Berry,\nSteven Jacobsen and an anonymous reviewer helped us refine\nthe manuscript. Finally, we once again thank all of the original\ndonors who provided samples for the study of Miller et al. [1987],\nand especially Masao Kitamura, for continuing use of his samples\nfrom Buell Park.\n", revision_no = "17", abstract = "Constraints on water storage capacity and actual content in the mantle must be\nderived not only from experimental studies, but also from investigation of natural\nsamples. Olivine is one of the best-studied, OH-bearing \"nominally anhydrous\"\nminerals, yet there remain multiple hypotheses for the incorporation mechanism of\nhydrogen in this phase. Moreover, there is still debate as to whether the mechanism\nis the same in natural samples vs. experimental studies, where concentrations can\nreach very high values (up to ~0.6 wt% H_2O) at high pressures and temperatures.\nWe present new observations and review IR and TEM data from the literature that\nbear on this question. Hydrogen incorporation in natural olivine clearly occurs\nby multiple mechanisms, but in contrast to some previous assertions we find that\nthere are strong similarities between the IR signatures of experimentally annealed\nolivines and most natural samples. At low pressures (lower than ~2 GPa) in both\nexperiments and natural olivines, hydrogen incorporation might be dominated by\na humite-type defect, but the nature of the defect may vary even within a single\nsample; possibilities include point defects, planar defects and optically detectable\ninclusions. IR bands between 3300 and 3400 cm^(-1), ascribed previously to the influence\nof silica activity, are apparently related instead to increased oxygen fugacity.\nAt higher pressures in experiments, the IR band structure changes and hydrogen\nis probably associated with disordered point defects. Similar IR spectra are seen\nin olivines from xenoliths derived from deeper parts of the mantle (below South\nAfrica and the Colorado Plateau) as well as in olivines from the ultra-high pressure\nmetamorphic province of the Western Gneiss Region in Norway.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33875, title ="Effect of Al on the sharpness of the MgSiO_3 perovskite to post-perovskite phase transition", author = "Akber-Knutson, S. and Steinle-Neumann, G.", journal = "Geophysical Research Letters", volume = "32", number = "14", pages = "Art. No. L14303", month = "July", year = "2005", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-144353150", note = "© 2005 American Geophysical Union. Received 8 April 2005; revised 8 June 2005; accepted 13 June 2005; published 19 July 2005. We thank two anonymous reviewers and R. Caracas, E. J. Garnero, D. V. Helmberger, T. Lay, and L. Stixrude for\nhelpful comments. This work is funded by ASCI (U. S. D. O. E. contract W-7405-ENG-48) and the Bayerisches Geoinstitut Visitor Program.", revision_no = "13", abstract = "By means of static ab-initio computations we investigate the influence of Al on the recently discovered perovskite to post-perovskite phase transition in MgSiO_3. We examine three substitution mechanisms for Al in the two structures: MgSi → AlAl; SiSiO → AlAl□; and Si → AlH. The substitutions introducing oxygen vacancies (highly unfavorable, energetically) and water (favorable) both lower the 0 Kelvin transition pressure, whereas charge coupled substitution increases it relative to 105 GPa for pure MgSiO_3. From the transition pressures for 0, 6.25, and 100 mol% charge coupled Al_2O_3 incorporation and simple solution theories, we estimate the phase diagram of Al-bearing MgSiO_3 at low Al concentrations. Assuming the Clapeyron slope is independent of Al concentration, we find the perovskite-to-post-perovskite transition region to span 127–140 GPa, at 6.25 mol% Al_2O_3. When the upper pressure limit is bounded by the core-mantle boundary, the phase coexistence region has width 150 km.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33769, title ="Coupling of anatectic reactions and dissolution of accessory phases and the Sr and Nd isotope systematics of anatectic melts from a metasedimentary source", author = "Zeng, Lingsen and Saleeby, Jason B.", journal = "Geochimica et Cosmochimica Acta", volume = "69", number = "4", pages = "3671-3682", month = "July", year = "2005", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-111314803", note = "© 2005 Elsevier Ltd.\nReceived September 22, 2004; accepted in revised form February 25, 2005.\nSupport for this research was provided by NSF grants EAR-9815024 and EAR-0087347. We thank D.W. Mittlefehldt,\nE.B. Watson, K. Knesel, M. Wolf and an anonymous reviewer for critical comments and suggestions. We greatly appreciate their comments that helped us clarify and improve the quality of our manuscript.\nAssociate editor: D. Mittlefehldt", revision_no = "13", abstract = "Advances in field observations and experimental petrology on anatectic products have motivated us to investigate the geochemical consequences of accessory mineral dissolution and nonmodal partial melting processes. Incorporation of apatite and monazite dissolution into a muscovite dehydration melting model allows us to examine the coupling of the Rb-Sr and Sm-Nd isotope systems in anatectic melts from a muscovite-bearing metasedimentary source. Modeling results show that (1) the Sm/Nd ratios and Nd isotopic compositions of the melts depend on the amount of apatite and monazite dissolved into the melt, and (2) the relative proportion of micas (muscovite and biotite) and feldspars (plagioclase and K-feldspar) that enter the melt is a key parameter determining the Rb/Sr and ^(87)Sr/^(86)Sr ratios of the melt. Furthermore, these two factors are not, in practice, independent. In general, nonmodal partial melting of a pelitic source results in melts following one of two paths in ε_(Nd^-) ^(87)Sr/^(86)Sr ratio space. A higher temperature, fluid-absent path (Path 1) represents those partial melting reactions in which muscovite/biotite dehydration and apatite but not monazite dissolution play a significant role; the melt will have elevated Rb/Sr, ^(87)Sr/^(86)Sr, Sm/Nd, and ε_(Nd) values. In contrast, a lower temperature, fluid-fluxed path (Path 2) represents those partial melting reactions in which muscovite/biotite dehydration plays an insignificant role and apatite but not monazite stays in the residue; the melt will have lower Rb/Sr, ^(87)Sr/^(86)Sr, Sm/Nd, and ε_(Nd) values than its source. The master variables controlling both accessory phase dissolution (and hence the Sm-Nd system), and melting reaction (and hence the Rb-Sr systematics) are temperature and water content. The complexity in Sr-Nd isotope systematics in metasediment-derived melts, as suggested in this study, will help us to better understand the petrogenesis for those granitic plutons that have a significant crustal source component.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/3254, title ="Novel crystalline carbon-cage structure synthesized from laser-driven shock wave loading of graphite", author = "Luo, Sheng-Nian and Tschauner, Oliver", journal = "Journal of Chemical Physics", volume = "123", number = "2", pages = "Art. No. 022703", month = "July", year = "2005", issn = "0021-9606", url = "https://resolver.caltech.edu/CaltechAUTHORS:LUOjcp05", note = "©2005 American Institute of Physics \n\n(Received 14 March 2005; accepted 20 May 2005; published online 18 July 2005) \n\nOne of the authors S.N.L. was sponsored by a Director’s Postdoctoral Fellowship at LANL. We are grateful for the invaluable support from the Trident laser facility/staff and the Inertial Confinement Fusion program at LANL. Another author (O.T.) acknowledges support by the NNSA Cooperative Agreement No. DE-FC88-01NV14049. Use of the HPCAT facility at APS was supported by DOE-BES, DOENNSA, NSF, DOD-TACOM, and the W. M. Keck Foundation. APS at Argonne National Laboratory is a national synchrotron-radiation light source research facility funded by the U.S. Department of Energy under Contract No. W-31-109-ENG-38. This work was performed in part under the auspices of U.S. Department of Energy under Contract No. W-7405-ENG-36.", revision_no = "8", abstract = "We report a novel crystalline carbon-cage structure synthesized from laser-driven shock wave loading of a graphite-copper mixture to about 14±2 GPa and 1000±200 K. Quite unexpectedly, it can be structurally related to an extremely compressed three-dimensional C60 polymer with random displacement of C atoms around average positions equivalent to those of distorted C60 cages. Thus, the present carbon-cage structure represents a structural crossing point between graphite interlayer bridging and C60 polymerization as the two ways of forming diamond from two-dimensional and molecular carbon.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/56988, title ="Thermodynamics of the lowermost mantle", author = "Sun, D. and Ahrens, T. J.", journal = "Geochimica et Cosmochimica Acta", volume = "69", number = "10", pages = "A253", month = "May", year = "2005", doi = "10.1016/j.gca.2005.03.027", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150427-082615873", note = "© 2005 Elsevier Ltd.", revision_no = "10", abstract = "Seismic observations of the region above the core mantle boundary (CMB), including Ultra-Low Velocity Zones (ULVZ) and D” discontinuities, and recent mineral physics data suggest the bottom of the mantle may be chemically heterogeneous, possibly, on account of the occurrence of the recently discovered post-perovskite (CaIrO_3) structure. Moreover, the large decrease in shear wave velocity in selected areas (ULVZ) in the lowermost 40 km of the mantle indicates the likely presence of partially molten material. To provide a complete petrologic and mineral physics model of this region, it is important to define both constituent material properties and phase equilibria including melting behavior. We expect to describe models that encompass the entire MgOFeO-CaO-Al_2O_3-SiO_2 system and to define complete mineral physics equations of state, employing thermochemical data to obtain complete phase diagrams. Our mineral physics-based seismic models are to be obtained using global inversion methods. Initial model results are reported for the SiO_2-MgO system.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33895, title ="Effect of water on magma and crustal density: Highly fractionated lavas in the Lau Basin and other wet spreading centers", author = "Langmuir, Charles H. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "69", number = "10", pages = "A149", month = "May", year = "2005", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-091801385", note = "© 2005 Pergamon-Elsevier Science Ltd.", revision_no = "14", abstract = "Mid-ocean ridges worldwide typically erupt basalts with\napproximately 8% MgO. This can be understood if eruption is\nprimarily controlled by the density of magmas relative to the\ncrust: high-MgO primary MORB is denser than the porous\nlayer 2 of oceanic crust, leading to ponding and fractionation.\nStolper & Walker (1980) and Sparks et al. (1980) pointed out\nthe density minimum along the tholeiitic liquid line of descent\nat plagioclase saturation, close to typical MORB composition.\nCertain regions, however, erupt anomalously fractionated\nlavas. Hotspot-affected and back-arc ridges tend towards\nvalues near 6% MgO and a few are dominated by andesites\nwith <4% MgO. An outstanding example is the southern end\nof the Eastern Lau Spreading Center, particularly the Valu Fa\nRidge, sampled by the Lau II Cruise (Leg 0417 of R/V Kilo\nMoana) in Fall 2004. Data show a systematic trend towards\nhighly fractionated samples with proximity to the Tonga\ntrench, including axial andesites and dacites. As pointed out\nfor calc-alkaline lavas by Grove and Baker (1983), water\nlowers the density of magma and the effect increases with\nextent of fractionation because water is incompatible and\nbecause it suppresses plagioclase fractionation. MELTS\ncalculations show that these effects together eliminate the\ndensity minimum for primary MORB lavas with >0.4% H_2O.\nTogether with increasing porosity of the upper crust\n(confirmed by seismic data), this effect of water provides a\nneat explanation for the decrease in mean MgO with\nmoderately elevated H_2O and the rather sudden transition to\nhighly fractionated samples at higher H_2O concentrations.\nThis is a regional effect and results from feedback between the\ndensity of roof-rocks derived from earlier dikes and eruptions\nwith the material in the present magma chamber.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33725, title ="Melt thermodynamics and divalent element partitioning between anorthite and CMAS liquids", author = "Miller, S. A. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "69", number = "10", pages = "A822", month = "May", year = "2005", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-152746549", note = "© 2005 Pergamon-Elsevier Science Ltd.", revision_no = "14", abstract = "Quantifying the effect of melt composition on trace\nelement partitioning in natural systems has been hampered by\ncorrelated variations in mineral chemistry, temperature, and\npressure. We have isolated the influence of melt composition\non divalent element (Mg, Ca, Sr, Ba) partitioning between\nstoichiometric anorthite and a range of synthetic melts. Data were obtained from electron microprobe analysis of anorthite rims from dynamic crystallization experiments. Melt compositions contain near constant SiO_2, CaO/Al_2O_3 ranging from 0.8-1.6, and MgO from 1-15 wt. %. Holding X_(mineral), T, and P constant, we observe partitioning behavior that varies systematically with melt chemistry.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33916, title ="On the sharpness of the perovskite/post-perovskite transition in the Earth's mantle", author = "Akber-Knutson, Sofia and Steinle-Neumann, Gerd", journal = "Geochimica et Cosmochimica Acta", volume = "69", number = "10", pages = "A252-A252", month = "May", year = "2005", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-144708844", note = "© 2005 Pergamon-Elsevier Science Ltd.", revision_no = "14", abstract = "The phase transition of pure MgSiO_3 perovskite (Pbnm) to\nthe post-perovskite (Cmcm) structure has been recently\nreported to occur at pressures and temperatures corresponding\nto the Earth’s lowermost mantle [Murakami et al. 2004,\nTsuchiya et al. 2004, Oganov and Ono 2004]. We use ab initio\ncalculations to assess whether this transition survives, in the\nEarth, for more realistic mantle compositions containing Al,\nFe^(2+), and Fe^(3+). We estimate phase coexistence pressures as\nfunctions of minor element concentration, and from this we\nobtain the effects of Al and Fe on the depth and sharpness of\nthe transition. For a pyrolitic mantle composition, with all the\nAl partitioned into MgSiO_3, we find that Al preferentially\npartitions into perovskite, and increases the transition pressure\nby approximately 5 GPa. The transition takes place over a\ndepth range of width 225 km. Fe competes with Al by\nlowering the transition pressure [Mao et al. 2004], so that\npost-perovskite is likely to exist in the lower mantle.\nHowever, the transition is still smooth, and not likely to\nexplain the sharp discontinuities observed seismically at the\nbase of the mantle. Our results suggest the geodynamical\nimplications of the post-perovskite phase transition require reevaluation.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1088, title ="Adiabat_1ph: A new public front-end to the MELTS, pMELTS, and pHMELTS models", author = "Smith, Paula M. and Asimow, Paul D.", journal = "Geochemistry, Geophysics, Geosystems", volume = "6", number = "1", pages = "2004GC000816", month = "February", year = "2005", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:SMIggg05", note = "Copyright 2005 by the American Geophysical Union \n\nReceived: 4 February 2002; Revised: 5 June 2002; Accepted: 27 June 2002; Published: 26 March 2003. \n\nWe are greatly indebted to Mark Ghiorso, who allowed us to use and adapt his source code and to release binaries incorporating many of the subroutines from his MELTS and pMELTS programs. Peter Luffi found and tracked down the garnet error, and Dan McKenzie helped with partition coefficient coding. Laura Baker, Louise Edwards, and Erik Hauri have bravely test-driven the beta versions and helped us make the software and documentation more user friendly. P. Asimow and P. Smith were supported for this work by the National Science Foundation (OCE-0241716 and EAR-0239513, respectively).", revision_no = "8", abstract = "The program adiabat_1ph is a simple text-menu driver for subroutine versions of the algorithms MELTS, pMELTS, and pHMELTS [Asimow et al., 2004; Ghiorso et al., 2002; Ghiorso and Sack, 1995]. It may be used to calculate equilibrium assemblages along a thermodynamic path set by the user and can simultaneously calculate trace element distributions. The MELTS family of algorithms is suitable for multicomponent systems, which may be anhydrous, water-undersaturated, or water-saturated, with the options of buffering oxygen fugacity and/or water activity. A wide variety of calculations can be performed either subsolidus or with liquid(s) present; melting and crystallization may be batch, fractional, or continuous. The software is suitable for Linux, MacOS X, and Windows, and many aspects of program execution are controlled by environment variables. Perl scripts are also provided that may be used to invoke adiabat_1ph with some command line options and to produce output that may be easily imported into spreadsheet programs, such as Microsoft Excel. Benefits include a batch mode, which allows almost complete automation of the calculation process when suitable input files are written. This technical brief describes version 1.04, which is provided as ancillary material. Binaries, scripts, documentation, and example files for this and future releases may be downloaded at http://www.gps.caltech.edu/~asimow/adiabat. On a networked computer, adiabat_1ph automatically checks whether a newer version is available.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33989, title ="Nd isotope disequilibrium during crustal anatexis: A record from the Goat Ranch migmatite complex, southern Sierra Nevada batholith, California", author = "Zeng, Lingsen and Saleeby, Jason B.", journal = "Geology", volume = "33", number = "1", pages = "53-56", month = "January", year = "2005", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120911-102914889", note = "© 2005 Geological Society of America.\n\nManuscript received 20 May 2004.\nRevised manuscript received 15 September 2004.\nManuscript accepted 22 September 2004.\n\nSupport for this research was provided by National Science Foundation\ngrants EAR-9815024 and EAR-0087347. We thank Jay Ague and Jon Davidson\nfor critical comments and suggestions.", revision_no = "15", abstract = "Geological and geochemical studies of a pelitic migmatite complex within the Isabella pendant of the southern Sierra Nevada batholith, California, suggest that the leucosomes represent the products of partial melting of the metapelite host driven by the emplacement of the adjacent Goat Ranch pluton ca. 100 Ma. The leucosomes preserve a record of large-magnitude Nd isotope disequilibrium with respect to their pelitic source. The leucosomes have a wide range of ε_(Nd(100 Ma)) from −6.0 to −11.0, as compared to −8.7 to −11.3 for the source. They can be subdivided into two groups based on their major elements and Sr and Nd isotope geochemistry. Group I leucosomes have higher P_2O_5 contents and ε_(Nd(100 Ma)) values than those of group II. The ε_(Nd(100 Ma)) values of group I leucosomes are significantly higher than those of metapelites and migmatites by two to four epsilon units, suggesting that group I leucosomes are in Nd isotope disequilibrium with their sources. Correlations among P_2O_5 contents, ε_(Nd(100 Ma)) values, and Sm/Nd ratios in the leucosomes suggest that apatite or monazite has played a dominant role in fractionating Sm from Nd and generating Nd isotope disequilibrium. Dissolution of apatite or monazite might play a critical role in regulating the behavior of the Sm-Nd isotope systems and thus the Nd isotope compositions of melts generated during crustal anatexis, especially in metasedimentary protoliths.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33846, title ="Laser-induced shock waves in condensed matter: some techniques and applications", author = "Luo, S. N. and Swift, D. C.", journal = "High Pressure Research", volume = "24", number = "4", pages = "409-422", month = "December", year = "2004", issn = "0895-7959", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-083611053", note = "© 2004 Taylor & Francis Ltd. One of the authors (S.N.L.) is sponsored by a Director's Postdoctoral Fellowship at LANL.\nThe authors are grateful for the invaluable support from the Trident laser facility and staff at\nLANL. O.T. acknowledges support by the NNSA Cooperative Agreement DE-FC88-\n01NV14049. Use of the HPCAT facility was supported by DOE-BES, DOE-NNSA, NSF,\nDOD-TACOM, and the W.M. Keck Foundation. This work was performed in part under\nthe auspices of US Department of Energy under contract #W-7405-ENG-36.", revision_no = "17", abstract = "Laser-induced shock waves in condensed matter have important applications in dynamic material studies and high pressure physics. We briefly review some techniques in laser-induced shock waves, including direct laser drive, laser-launched flyer plate, quasi-isentropic loading, point and line imaging velocity interferometry, transient X-ray diffraction, spectroscopy and shock recovery, and their applications to study of equation of state, spallation, and phase transitions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33850, title ="Shock-synthesized glassy and solid silica: Intermediates between four- and six-fold coordination", author = "Tschauner, O. and Luo, S. N.", journal = "High Pressure Research", volume = "24", number = "4", pages = "471-479", month = "December", year = "2004", issn = "0895-7959", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-093417118", note = "© 2004 Taylor & Francis Ltd. Version of record first published: 26 Jan 2007. This work was supported by NNSA Cooperative Agreement DE-FC88-01NV14049. Some\nmaterial used in this study is based on work supported by the NASA/Goddard Award no.\nNNG04G 107G, Division of Geological and Planetary Sciences, California Institute of Technology\nand NASA Grant NAGS-10198. S.N.L. is sponsored by a Director's Postdoctoral Fellowship\nat LANL. We are grateful for the invaluable support from the Trident laser facility\nand staff at LANL. Use of the HPCAT facility was supported by DOE-BES, DOE-NNSA,\nNSF, DOD-TACOM, and the W.M. Keck Foundation. Use of the APS was supported\nby the US Department of Energy, Basic Energy Sciences, Office of Energy Research\nunder contract no. W -31-1 09-Eng-38. This work was partly performed at Los Alamos\nNational Laboratory under the auspices of the US Department of Energy under contract\nno. W-7405-ENG-36. ", revision_no = "33", abstract = "Upon compression, many materials undergo major reconstructions of their structure and bonding, including increases in coordination of atoms and changes in bonding character. While transforming, the materials pass through intermediate states, which are often too transient to be captured and examined. Here we discuss the coordination change in silica as an example of a system where such interesting intermediate structural states have been quenched from shock-experiments. On the basis of these results we suggest a relation between the formation of one of these phases and the extension of the liquid–liquid transition boundary into the stability field of solid silica. We report Raman spectra of shock-retrieved vitreous silica which indicate different compression mechanisms for shock-generated amorphous silica and vitreous silica compressed at 300 K. Static recompression of shock-generated glass leads to an amorphous-crystal transition above 13 GPa.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1461, title ="The Significance of Multiple Saturation Points in the Context of Polybaric Near-fractional Melting", author = "Longhi, John and Asimow, Paul D.", journal = "Journal of Petrology", volume = "45", number = "12", pages = "2349-2367", month = "December", year = "2004", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:ASIjpet04", note = "Copyright © 2004 Oxford University Press. Reprinted with permission.\n\nRECEIVED JULY 2, 2003; ACCEPTED APRIL 6, 2004; Journal of Petrology Advance Access published on August 19, 2004 \n\nThis paper was motivated by a stimulating conversation with D. H. Green, an invitation to speak at the 2002 Fall AGU Bowen symposium meeting from M. S. Ghiorso and D. Geist, and the hope that M. J. O'Hara will find it intriguing. We acknowledge helpful reviews by C. T. Herzberg and C. C. Lundstrom. It is not our intent to belittle the contributions of experimentalists who have laboured to collect liquidus data over the years in pursuit of multiple saturation points; these experiments have in fact proven essential for calibration of high-pressure melting and fractionation models such as those applied in this study. P.D.A. acknowledges support from the National Science Foundation (OCE-0241716 and EAR-0239513). J.L. acknowledges support from the National Science Foundation (OCE-0084098) and NASA (NAG 5-4649). This is Division of Geological and Planetary Science contribution 8961.", revision_no = "8", abstract = "Experimental petrologists have successfully located basaltic liquid compositions parental to mid-ocean ridge basalt that are, within experimental resolution, multiply saturated with three-phase harzburgite or four-phase lherzolite assemblages on their liquidus at some elevated pressure. Such an experimental result is a necessary consequence of any paradigm in which erupted basalts derive from single-batch primary liquids that equilibrate with a mantle residue and undergo no subsequent magma mixing before differentiation and eruption. Here we investigate whether, conversely, such evidence of multiple saturation is sufficient to exclude dynamic melting models wherein increments of melt are mixed after segregation from residues, during melt transport or in magma chambers. Using two independent models of crystal–liquid equilibria to simulate polybaric near-fractional peridotite melting, we find that aggregate liquids from such melting processes can display near-intersections of liquidus surfaces too close to distinguish experimentally from exact multiple saturation points. Given uncertainties in glass compositions, fractionation corrections, experimental temperature and pressure conditions, and achievement of equilibrium, these results suggest that polybaric mixtures can in fact masquerade as mantle-equilibrated single-batch primary liquids. Multiple saturation points on the liquidus surfaces of primitive basalts do, however, preserve information about the average pressure of extraction of their constituent increments of liquid.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33797, title ="Shock-induced melting of MgSiO_3 perovskite and implications for melts in Earth's lowermost mantle", author = "Akins, Joseph A. and Luo, Sheng-Nian", journal = "Geophysical Research Letters", volume = "31", number = "14", pages = "Art. No. L14612", month = "July", year = "2004", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-143626223", note = "© 2004 American Geophysical Union. \n\nReceived 12 April 2004; accepted 2 July 2004; published 30 July 2004. \n\nThis work was funded by the National Science Foundation through grants EAR-9903806 and EAR-0207934. Thanks to Carl Francis and Stephen Mackwell for providing the high\nquality Sri Lankan enstatites used in this study. The authors thank an anonymous reviewer and editor Kristine Larson for their help improving the manuscript. This is Caltech GPS contribution #9046.", revision_no = "15", abstract = "New shock wave equation of state (EOS) data for enstatite and MgSiO_3 glass constrain the density change upon melting of Mg-silicate perovskite up to 200 GPa. The melt becomes denser than perovskite near the base of Earth's lower mantle. This inference is confirmed by shock temperature data suggesting a negative pressure-temperature slope along the melting curve at high pressure. Although melting of Earth's mantle involves multiple phases and chemical components, this implies that the partial melts invoked to explain anomalous seismic velocities in the lowermost mantle may be dynamically stable. ", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/2235, title ="Time-Resolved X-Ray Diffraction Investigation of Superheating-Melting of Crystals under Ultrafast Heating", author = "Luo, Sheng-Nian and Swift, Damian C.", number = "706", pages = "95-98", month = "July", year = "2004", isbn = "0735401810", url = "https://resolver.caltech.edu/CaltechAUTHORS:LUOaipcp04b", note = "© 2004 American Institute of Physics.\n\nS.-N. Luo is sponsored by a Director's Postdoctoral Fellowship at Los Alamos National Laboratory (P-24 and EES-11). We appreciate the kind permission of QinetiQ for using their exploding wire data.", revision_no = "12", abstract = "The maximum superheating of a solid prior to melting depends on the effective dimensionless nucleation energy barrier, heterogeneities such as free surfaces and defects, and heating rates. Superheating is rarely achieved with conventional slow heating due to the dominant effect of heterogeneous nucleation. In present work, we investigate the superheating-melting behavior of crystals utilizing ultrafast heating techniques such as exploding wire and laser irradiation, and diagnostics such as time-resolved X-ray diffraction combined with simultaneous measurements on voltage and current (for exploding wire) and particle velocity (for laser irradiation). Experimental designs and preliminary results are presented.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33728, title ="Petrology of the lowermost mantle", author = "Asimow, Paul D. and Sun, D", journal = "Geochimica et Cosmochimica Acta", volume = "68", number = "11", pages = "A561", month = "June", year = "2004", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-153419650", note = "© 2004 Pergamon-Elsevier Science Ltd.", revision_no = "17", abstract = "Seismic observations of the thermal boundary layer above\nthe core-mantle boundary (CMB), including Ultra-Low\nVelocity Zones and D\" discontinuities with velocity jumps of\neither sign, suggest that the bottom of the mantle may be\ncompositionally distinct and, in places, partially molten[1].\nOur new shock-wave data constrain the melting curve and\nliquid equation of state (EOS) of the key lower mantle\ncomponent MgSiO_3 perovskite and suggest neutral or negative\nbuoyancy of this melt at CMB pressure.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33874, title ="Shock-compressed MgSiO_3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting", author = "Luo, Sheng-Nian and Akins, Joseph A.", journal = "Journal of Geophysical Research B", volume = "109", number = "B5", pages = "Art. No. B05205", month = "May", year = "2004", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-142013132", note = "© 2004 American Geophysical Union. Received 20 October 2003; revised 3 March 2004; accepted 10 March 2004; published 11 May 2004. This work was supported by U.S. National Science Foundation Grant No. EAR-0207934 (TJA and PDA). SNL is sponsored by a Director’s Post-doctoral Fellowship at Los Alamos National Laboratory (P-24 and EES-11). P. Gelle, M. Long and C. McCaughey supplied invaluable technical support. G. R. Rossman and E. Arrendondo kindly helped with optical spectroscopy measurements. C. Francis and S. Mackwell supplied the high-quality Sri Lanka enstatite crystals. We also benefited from discussions with X. L. Huang, S. D. Ni and D. C. Swift. The constructive suggestions by D. Heinz and I. Jackson are highly appreciated. Contribution No. 8951, Division of Geological and Planetary Sciences,\nCalifornia Institute of Technology.", revision_no = "12", abstract = "Optical emission of MgSiO_3 glass, enstatite, olivine, and quartz under shock wave compression was investigated with optical pyrometry at discrete wavelengths ranging from visible to near infrared. We develop a new analysis of optical emission that does not require a gray body assumption. Instead, at each wavelength, the optical linear absorption coefficients (α) and blackbody spectral radiances (L_(λb)) of shocked and unshocked materials were obtained by nonlinear fitting to the time-resolved radiance from the target assembly. The absorption spectra of unshocked samples corresponding to the measured values of α reproduce those from independent static optical spectroscopic measurements. The measured values of α (ranging from 7 to 56 mm^(−1)) for shocked samples indicate that shock-induced high-pressure phases (including melt) can be regarded essentially as black bodies in the optical range investigated, although starting phases such as enstatite and olivine have band-like spectra at ambient conditions. The effect of emission from the air gap at the driver sample interface on the recorded radiance can be resolved, but α and L_(λb) cannot be separated for this component of the signal. The shock velocity-particle velocity relationships of these silicates derived from radiance history are in accord with previous investigations using independent techniques. Given the limited amount of shock wave data, possible high-pressure melting curves of Mg-perovskite and its assemblage with periclase are deduced; their melting temperatures near the core-mantle boundary (CMB) being 6000 ± 500 K and 4000 ± 300 K, respectively. It is proposed that Mg-perovskite melts with density increase at the CMB pressure. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33825, title ="Acceptance of the 2003 F. W. Clarke Award", author = "Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "68", number = "9", pages = "1965-1966", month = "May", year = "2004", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120904-141201954", note = "© 2004 Elsevier Ltd.", revision_no = "16", abstract = "Thank you, Ed, for your kind words and moreover for all the air travel hours that you endured specifically to come here and say them. But don’t fly home just yet because I’ll be thanking you more shortly. Thank you also to the Clarke medal committee and the Geochemical Society for this wonderful honor.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33765, title ="Oxygen isotope evidence for the origin of enriched mantle\nbeneath the mid-Atlantic ridge", author = "Cooper, Kari M. and Eiler, John M.", journal = "Earth and Planetary Science Letters", volume = "220", number = "3-4", pages = "297-316", month = "April", year = "2004", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-104940451", note = "© 2004 Elsevier B.V.\nReceived 15 March 2003; received in revised form 4 September 2003; accepted 12 January 2004.\nWe thank the OCE and Margins programs of the US National Science Foundation (grants to J.M.E.) and the Moore Foundation for a grant to Caltech that supported this research. We thank the captain and crew of the RV Atlantis\nII for their assistance during collection of the samples used in this study. Reviews by S. Shirey and an anonymous reviewer improved the quality of the manuscript. This is division of Geological and Planetary Sciences contribution\n9049.[BW]", revision_no = "14", abstract = "Geochemical variations in mid-ocean ridge basalts have been attributed to differing proportions of compositionally distinct mantle components in their sources, some of which may be recycled crust. Oxygen isotopes are strongly fractionated by near-surface interactions of rocks with the hydrosphere, and thus provide a tracer of near-surface materials that have been recycled into the mantle. We present here oxygen isotope analyses of basaltic glasses from the mid-Atlantic ridge south of and across the Azores platform. Variations in δ^(18)O in these samples are subtle (range of 0.47‰) and may partly reflect shallow fractional crystallization; we present a method to correct for these effects. Relatively high fractionation-corrected δ^(18)O in these samples is associated with geochemical indices of enrichment, including high La/Sm, Ce/Pb, and ^(87)Sr/^(86)Sr and low ^(143)Nd/^(144)Nd. Our results suggest two first-order conclusions about these enriched materials: (1) they are derived (directly or indirectly) from recycled upper oceanic crustal rocks and/or sediments; and (2) these materials are present in the north Atlantic MORB sources in abundances of less than 10% (average 2–5%). Modeling of variations of δ^(18)O with other geochemical variables further indicates that the enriched component is not derived from incorporation of sediment or bulk altered oceanic crust, from metasomatism of the mantle by hydrous or carbonate-rich fluids, or from partial melting of subducted sediment. Instead, the data appear to require a model in which the enriched component is depleted mantle that has been metasomatized by small-degree partial melts of subducted, dehydrated, altered oceanic crust. The age of this partial melting is broadly constrained to ∼250 Ma. Reconstructed plate motions suggest that the enriched component in the north Atlantic mantle may have originated by subduction along the western margin of Pangea.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33701, title ="A new dense silica polymorph: A possible link between tetrahedrally and octahedrally coordinated silica", author = "Luo, Sheng-Nian and Tschauner, Oliver", journal = "American Mineralogist", volume = "89", number = "2-3", pages = "455-461", month = "February", year = "2004", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-094450477", note = "© 2004 Mineralogical Society of America.\n\nManuscript Received August 5, 2003; manuscript Accepted November 17, 2003.\n\nThis work was supported by NSF Grant EAR-0207934 and NASA Grant NAG5-10198. S.N.L. was also sponsored by a Director’s Post-doctoral Fellowship at Los Alamos National Laboratory (P-24 and EES-11). O.T. also acknowledges support from NNSA Cooperative Agreement DE-FC88-01NV14049. We appreciate the help of G.R. Rossman and E. Arredondo in Raman spectroscopy, P. Dera, C. Prewitt, R.J. Hemley, and H.K. Mao for kind permission to use their X-ray diffraction and CO2-laser heating facilities. We thank P. Dera and two anonymous reviewers for helpful comments. Contribution no. 8943, Division of Geological and Planetary Sciences, California Institute of Technology. ", revision_no = "17", abstract = "We present the discovery of a novel dense silica polymorph retrieved from shock-wave and diamond-anvil cell experiments. This polymorph is the first observed silicate composed of face-sharing polyhedra and it has a density similar to stishovite. Sterical constraints on the bond angles induce an intrinsic disorder of Si positions, such that the Si-coordination is transitional between four-and sixfold. The structure provides a mechanism for this coordination change in silica and other silicates at high temperature that is fundamentally different from mechanisms at 300 K. The new polymorph also illustrates how the face-sharing polyhedra, naturally occurring along previously proposed compression mechanisms for dense silicate melts, can be constructed without inferring unphysically small bond angles. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1090, title ="A hydrous melting and fractionation model for mid-ocean ridge basalts: Application to the Mid-Atlantic Ridge near the Azores", author = "Asimow, Paul D. and Dixon, J. E.", journal = "Geochemistry, Geophysics, Geosystems", volume = "5", number = "1", pages = "2003GC000568", month = "January", year = "2004", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:ASIggg04", note = "Copyright 2004 by the American Geophysical Union. \n\nReceived 11 April 2003; Revised 21 October 2003; Accepted 18 November 2003; Published 28 January 2004. \n\nPDA thanks Mark Ghiorso for allowing his code to be so mercilessly hacked. PDA was supported for part of this work by a postdoctoral fellowship from Lamont-Doherty Earth Observatory and later by the National Science Foundation (OCE 00-95294). CHL and JED acknowledge support by multiple grants from NSF over a period of years. This is Division of Geological and Planetary Sciences contribution number 8913.", revision_no = "8", abstract = "The major element, trace element, and isotopic composition of mid-ocean ridge basalt glasses affected by the Azores hotspot are strongly correlated with H2O content of the glass. Distinguishing the relative importance of source chemistry and potential temperature in ridge-hotspot interaction therefore requires a comprehensive model that accounts for the effect of H2O in the source on melting behavior and for the effect of H2O in primitive liquids on the fractionation path. We develop such a model by coupling the latest version of the MELTS algorithm to a model for partitioning of water among silicate melts and nominally anhydrous minerals. We find that much of the variation in all major oxides except TiO2 and a significant fraction of the crustal thickness anomaly at the Azores platform are explained by the combined effects on melting and fractionation of up to ~700 ppm H2O in the source with only a small thermal anomaly, particularly if there is a small component of buoyantly driven active flow associated with the more H2O-rich melting regimes. An on-axis thermal anomaly of ~35°C in potential temperature explains the full crustal thickness increase of ~4 km approaching the Azores platform, whereas a ≥75°C thermal anomaly would be required in the absence of water or active flow. The polybaric hydrous melting and fractionation model allows us to solve for the TiO2, trace element and isotopic composition of the H2O-rich component in a way that self-consistently accounts for the changes in the melting and fractionation regimes resulting from enrichment, although the presence and concentration in the enriched component of elements more compatible than Dy cannot be resolved.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/56882, title ="Synthesis and thermoelectric properties of Ce(Ru_(0.67)Rh_(0.33)_4Sb_(12)", author = "Staneff, Geoff D. and Asimow, Paul D.", number = "793", pages = "101-106", month = "January", year = "2004", doi = "10.1557/PROC-793-S4.3", isbn = "9781558997318", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150422-135839092", note = "© 2004 Materials Research Society.\n\nThis work was made possible through the assistance and guidance of the\nThermoelectrics group at the Jet Propulsion Laboratory. The author would also like to thank cerium, ruthenium, rhodium, and antimony; without them this work would not have been possible.", revision_no = "10", abstract = "Exotic filled skutterudite compositions show promise for thermoelectric applications. Current work was undertaken with a nominal composition of Ce(Ru_(0.67)Rh_(0.33))_4Sb_(12) to experimentally verify its potential as an n-type thermoelectric material. Nominal electroneutrality was expected at 0.89 cerium filling and fully filled materials were expected to be strongly n-type. Filled precursors of the nominal composition were synthesized using straightforward solid state reaction techniques, but standard synthesis routes failed to produce a fully-filled homogenous phase. Instead, the filled thermoelectric Ce(Ru_(0.67)Rh_(0.33))_4Sb_(12) was synthesized using a combination of solid state reaction of elemental constituents and high pressure hot pressing. A range of pressure-temperature conditions was explored; the upper temperature limit of filled skutterudite in this system decreases with increasing pressure and disappears by 12 GPa. The optimal synthesis was performed in multi-anvil devices at 4–6 GPa pressure and dwell temperatures of 350–700 °C. rutheniumThe result of this work, a Ce(Ru_(0.67)Rh_(0.33))_4Sb_(12) fully filled skutterudite material, exhibited unexpected p-type conductivity and an electrical resistance of 1.755 mΩ-cm that increased with temperature. Thermal conductivity, Seebeck coefficient, and resistivity were measured on single phase samples. In this paper, we report the details of the synthesis routeand measured thermoelectric properties, speculate on the deviation from expected carrier charge balance, and discuss implications for other filled skutterudite systems.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33873, title ="Polymorphism, superheating, and amorphization of silica upon shock wave loading and release", author = "Luo, Sheng-Nian and Ahrens, Thomas J.", journal = "Journal of Geophysical Research B", volume = "108", number = "B9", pages = "Art. No. 2421", month = "September", year = "2003", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-141101974", note = "© 2003 American Geophysical Union. Received 21 November 2002; revised 12 May 2003; accepted 23 May 2003; published 10 September 2003. S.-N. Luo has been supported by NSF grant\nEAR-0207934. We appreciate helpful discussions with Z. R. Wang, D. Andrault, and O. Tschauner. Comments by I. Jackson and two reviewers helped improve the manuscript. Contribution 8916, Division of Geological and Planetary Sciences, California Institute of Technology", revision_no = "12", abstract = "We present a detailed and quantitative examination of the thermodynamics and phase change mechanisms (including amorphization) that occur upon shock wave loading and unloading of silica. We apply Debye-Grüneisen theory to calculate both the Hugoniot of quartz and isentropic release paths. Quartz converts to stishovite (or a stishovite-like phase) between 15 and 46 GPa, and persistence of the solid phase above its liquidus (i.e., superheating) is confirmed between 77 and 110 GPa. Calculations compare favorably to measurements of shock and post-shock temperatures. For silica, the method of measuring post-shock temperature is insensitive to predicting whether phase transitions actually occur during release. Measurements of release states in pressure-particle velocity space are compared to computed frozen-phase release paths. This comparison suggests transformation of a stishovite-like phase to lower density phases including quartz, liquid, or dense amorphous glass. Transformations to liquid or glass occur upon release from peak pressure of 26 GPa and above. The isentropic release assumption appears to be approximately valid. A shock pressure-temperature scale relating metamorphism of silica in shock-loaded quartz is proposed. Neither recovery of coesite nor substantial quantities of crystalline stishovite-like phases upon shock loading of quartz is predicted. Trace amounts of crystalline stishovite-like phases from shock loading between 15 and 26 GPa are expected.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39533, title ="Experimental evidence concerning the pressure dependence of He diffusion and fission-track annealing kinetics in apatite", author = "Donelick, R. and Farley, K.", journal = "On track: the newsletter of the international fission-track community", volume = "13", number = "2", pages = "19-21", month = "September", year = "2003", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130723-131212011", revision_no = "18", abstract = "We offer this short note to document data we\nhave collected regarding the pressure\ndependence of He diffusion and fission-track\nannealing kinetics in apatite. This work is a\ndirect result of the provocative EPSL paper by\nWendt et al. (2002). Should their data stand, so\nshould many of their conclusions. For the record,\nwe have communicated constructively with Anke\nWendt and through her, her co-authors, and we\nhave the singular goal of better understanding\ntheir data and the issues raised in their paper.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33705, title ="Pressure dependence of He diffusion and fission-track annealing kinetics in apatite?: Experimental results", author = "Donelick, R. and Farley, K.", journal = "Geochimica et Cosmochimica Acta", volume = "67", number = "18", pages = "A82", month = "September", year = "2003", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-104815559", note = "© 2003 Pergamon-Elsevier Science Ltd.", revision_no = "17", abstract = "A number of preliminary experiments have been\nundertaken to test results reported by Wendt et al. (2002),\nconcerning the dependancy of pressure on fission track\nannealing in apatite, and which implied a similar dependancy\nfor He difusion in apatite.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33827, title ="Systematics of water partitioning in damp mantle melting models", author = "Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "67", number = "18", pages = "A28", month = "September", year = "2003", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120904-145354460", note = "© 2003 Pergamon-Elsevier Science Ltd.", revision_no = "17", abstract = "In regions of the mantle where water is a trace species in\nthe nominally anhydrous minerals (rather than a free vapor\nphase or a hydrous mineral), melting is controlled by water\npartitioning into melt and the resulting freezing-point\ndepression. Modeling undersaturated melting therefore\nrequires a well-constrained formalism for the bulk partition\ncoefficient (D_(H_2O)) and its variations, as well as an accurate\nmodel for hydrous melt-mineral equilibria. Hirth and\nKohlstedt [1] developed a water partitioning model that leads\nto a solely pressure-dependent D_(H_2O). Their model expresses\nthe solubility of H_2O in minerals and melts as a function of the\nstandard state f°_(H_2O) (linear for minerals, square root\nfor melts). In the absence of data on undersaturated systems,\nthey assume Henry's law, such that D_(H_2O) is the ratio of\nsolubilities, at any water content. Thermodynamically,\nhowever, one expects a square root dependence of H_2O\ncontent in the melt on the actual water fugacity\n(f°_(H_2O) = a_(H_2O)f°_(H_2O)). This implies that D_(H_2O) decreases with\ndecreasing water content as a^(1/2) H_2O, approaching zero as the\nsystem dries out. The coupling of this partitioning model to\npMELTS is the basis of one approach to damp mantle melting\n[2]. The prediction of a concentration-dependent D_(H_2O) has\nsome important but difficult-to-observe consequences (e.g.,\nthe removal of H_2O from the residue would be an accelerating\nprocess, leading to a more abrupt viscosity transition) but also\nmakes the direct prediction that water should behave more\ncompatibly in more-water rich systems. There has been\nconsiderable argument as to which is the most appropriate\nanalogue trace element for water partitioning. Estimates have\nranged from (as incompatible as) La in depleted MORB to (as\ncompatible as) Nd in BABB [3], though Ce is presently a\npopular choice [4]. This variation can be a natural and\nsystematic consequence of partitioning rather than a complex\ncombination of source and process effects, and is due to the\nnon-Henrian behavior of water in the melt rather than a\npressure dependence. Direct mineral-melt water partitioning\ndata from undersaturated experiments are needed to test this\nprediction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33721, title ="Thermodynamic modelling of melting in chemically heterogenous mixtures of peridotite and pyroxenite", author = "Smith, P. M. and Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "67", number = "18", pages = "A440", month = "September", year = "2003", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-145528222", note = "© 2003 Pergamon-Elsevier Science Ltd.", revision_no = "15", abstract = "Melting of pyroxenite veins or layers has been proposed as\nan explanation for the 'garnet signature' in MORB and for\ncharacteristic source signatures in OIB. Recent experiments\nhave constrained the melt productivity of respresentative\npyroxenite compositions but pyroxenite melting in the\nconvecting mantle will be enhanced by heat transfer from the\nsurrounding peridotite. The algorithm DUAL ADIABA T is\nbased on the MELTS software package. - It calculates\nisentropic decompression paths for two lithologies that are in\nthermal but not chemical equilibrium. We have used\nDUAL_ADIABAT to compare the melting of variable\nproportions of pyroxenite and peridotite along typical mantle\nadiabats with and without chemical equilibrium between the\nsystems. The effects of melt extraction, homogenisation and\ntransport processes and melt-region geometry may be tested.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33754, title ="Earth science: A slice of history", author = "Asimow, Paul D.", journal = "Nature", volume = "423", number = "6939", pages = "491-493", month = "May", year = "2003", doi = "10.1038/423491a ", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-092532697", note = "© 2003 Nature Publishing Group.", revision_no = "14", abstract = "Investigations of an exposed slice of oceanic crust and mantle have provided a dramatic picture of temporal variation in the activity of the Mid-Atlantic Ridge — including its pulse rate of 3–4 million years.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1089, title ="PetroPlot: A plotting and data management tool set for Microsoft Excel", author = "Su, Yongjun and Langmuir, Charles H.", journal = "Geochemistry, Geophysics, Geosystems", volume = "4", number = "3", pages = "2002GC000323", month = "March", year = "2003", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:SUYggg03", note = "Copyright 2003 by the American Geophysical Union. \n\nReceived: 14 August 2004; Revised: 4 January 2005; Accepted: 5 January 2005; Published: 15 February 2005. \n\nColleagues in the LDEO petrology group have been loyal beta-testers for PetroPlot. Numerous feedback and suggestions from them have substantially improved the program. Comments from Dennis Geist, Bill White, Yaoling Niu, Peter Michael, and David Christie have greatly improved both functions and documentation of this software, and lead to the creation of the tutorial.\n\nAuxiliary material for this article contains PetroPlot source files as well as a detailed tutorial explaining how to install the PetroPlot package and how to use the PetroPlot package for plotting and manipulation of geochemical data in the Microsoft Excel environment. Additional file information is provided in the README.txt. Available at: http://www.agu.org/journals/gc/gc0303/2002GC000323/supplement.shtml", revision_no = "20", abstract = "PetroPlot is a 4000-line software code written in Visual Basic for the spreadsheet program Excel that automates plotting and data management tasks for large amount of data. The major plotting functions include: automation of large numbers of multiseries XY plots; normalized diagrams (e.g., spider diagrams); replotting of any complex formatted diagram with multiple series for any other axis parameters; addition of customized labels for individual data points; and labeling flexible log scale axes. Other functions include: assignment of groups for samples based on multiple customized criteria; removal of nonnumeric values; calculation of averages/standard deviations; calculation of correlation matrices; deletion of nonconsecutive rows; and compilation of multiple rows of data for a single sample to single rows appropriate for plotting. A cubic spline function permits curve fitting to complex time series, and comparison of data to the fits. For users of Excel, PetroPlot increases efficiency of data manipulation and visualization by orders of magnitude and allows exploration of large data sets that would not be possible making plots individually. The source codes are open to all users.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33713, title ="The importance of water to oceanic mantle melting regimes", author = "Asimow, Paul D. and Langmuir, C. H.", journal = "Nature", volume = "421", number = "6925", pages = "815-820", month = "February", year = "2003", doi = "10.1038/nature01429", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-132316368", note = "© 2003 Nature Publishing Group.\nReceived 20 November 2002; accepted 14 January 2003.\n\nWe thank P. Michael for comments and suggestions. This work was supported by the National Science Foundation. Competing interests statement: The authors declare that they have no competing financial interests.", revision_no = "16", abstract = "The formation of basaltic crust at mid-ocean ridges and ocean islands provides a window into the compositional and thermal state of the Earth's upper mantle. But the interpretation of geochemical and crustal-thickness data in terms of magma source parameters depends on our understanding of the melting, melt-extraction and differentiation processes that intervene between the magma source and the crust. Much of the quantitative theory developed to model these processes has neglected the role of water in the mantle and in magma, despite the observed presence of water in ocean-floor basalts. Here we extend two quantitative models of ridge melting, mixing and fractionation to show that the addition of water can cause an increase in total melt production and crustal thickness while causing a decrease in mean extent of melting. This may help to resolve several enigmatic observations in the major- and trace-element chemistry of both normal and hotspot-affected ridge basalts.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1462, title ="Steady-state Mantle–Melt Interactions in One Dimension: II. Thermal Interactions and Irreversible Terms", author = "Asimow, Paul D.", journal = "Journal of Petrology", volume = "43", number = "9", pages = "1707-1724", month = "September", year = "2002", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:ASIjpet02", note = "© Oxford University Press 2002. Reprinted with permission. \n\nReceived August 2, 2001; Revised typescript accepted March 26, 2002 \n\nThe author wishes most of all to thank Ed Stolper for his unselfish support throughout this project. Thanks also go to Frank Spera and an anonymous reviewer for helpful reviews, and to George Bergantz for editorial handling. Discussions with Marc Spiegelman and Dan McKenzie helped refine my understanding of dissipation. This work was supported by NSF grants OCE-9529878 and EAR-9219899 and by a Lamont–Doherty Earth Observatory postdoctoral fellowship. This is Caltech Division of Geological and Planetary Sciences Contribution 8801.", revision_no = "8", abstract = "Progress in development of thermodynamically based models of silicate equilibria with explicit entropy budgets has motivated a reexamination of the conclusion of McKenzie (Journal of Petrology 25, 713–765, 1984) that isentropic upwelling suffices as a model of mantle melting. An entropy budget equation for fractional melting with melt migration in an upwelling two-phase continuum is presented. The energetically self-consistent melt production model predicted by MELTS is used to evaluate numerically the magnitudes of differences between fractional melting (with melt migration) and equilibrium melting (without relative movement) that can be bounded in one dimension: chemical advection by out-of-equilibrium melt; thermal disequilibrium between migrating liquid and residue; frictional dissipation of gravitational potential; dissipation as a result of solid compaction. Like the familiar isobaric case in which fractional melting is significantly less productive than equilibrium melting, chemical isolation of the escaping melts from the residue reduces the oceanic crustal thickness by ~1 km. Allowing escaping melts to move on their own adiabats and ascend at higher temperature than the residue further suppresses melting but yields only ~100 m less crustal thickness. Extra crustal thickness as a result of gravitational dissipation is ~100 m, much smaller than the effect of chemical isolation. Viscous dissipation as a result of compaction is negligible.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33719, title ="Melt migration vs. isentropic decompression melting, more or less", author = "Asimow, Paul D.", journal = "Geochimica et Cosmochimica Acta", volume = "66", number = "15A", pages = "A34", month = "August", year = "2002", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-144751592", note = "© 2002 Pergamon-Elsevier Science Ltd.", revision_no = "14", abstract = "Decompression melting of the asthenospheric mantle is\nroutinely modelled as an isentropic process, but as\nthermodynamic models evolve to the point where this\nconstraint can be rigorously (and perhaps accurately) imposed,\nit becomes important to test the quality of this assumption. In\nparticular, as McKenzie (1984) recognised, when melt\nmigration occurs the upwelling is neither adiabatic nor\nreversible due to advection of heat by the melt and\ngravitational dissipation. McKenzie estimated that these\neffects were negligible relative to the rather large uncertainties\nin his melting parameters, but concluded that melt migration\nleads to excess melting above that generated in the isentropic\ncase, by at most 60%. However, relative movement of melt\nand solids has another first-order effect - the possibility of\nintroducing chemical disequilibrium, or something akin to\nfractional melting. It is well known that fractional melting\nprocesses are less productive in general than equilibrium\nmelting, so this raises the possibility that melt migration leads\nto substantially less melting and crustal production than the\nisentropic equilibrium case. In order to settle which of these\neffects is dominant and to bound the magnitude of both\neffects, I construct an energy equation similar to McKenzie's\nthat allows for chemical and thermal disequilibrium between\nmigrating melts and residues and perform a series of one-dimensional\nMELTS calculations that show the net melt\nproduction of various cases.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33897, title ="Oxygen-isotope evidence for altered oceanic crust in the Atlantic MORB source", author = "Cooper, Kari M. and Eiler, John M.", journal = "Geochimica et Cosmochimica Acta", volume = "66", number = "15A", pages = "A151-A151", month = "August", year = "2002", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-092507177", note = "© 2002 Pergamon-Elsevier Science Ltd.", revision_no = "14", abstract = "A long-wavelength geochemical gradient in Mid-Atlantic\nRidge (MAR) samples collected between 33 and 41°N has\npreviously been attributed to mixing of material from depleted\nand enriched (EMII-type) mantle components. Enriched\nmantle domains are principally identified using isotopes of\nincompatible trace elements, which can be dominated by small\nmass fractions of enriched material. Oxygen, by contrast,\noccurs in roughly constant abundance in most mantle and\ncrustal minerals and deviations from mantle δ^(18)O reflect near-surface\nprocesses; thus variations in δ^(18)O can be used to\nconstrain the percentage of recycled near-surface materials\nwithin a given source region. We present here high-precision\noxygen-isotope analyses of MAR glasses and discuss the\nimplications for the nature and percentage of the regional\nenriched component.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33872, title ="Direct shock wave loading of Stishovite to 235 GPa: Implications for perovskite stability relative to an oxide assemblage at lower mantle conditions", author = "Luo, Sheng-Nian and Mosenfelder, J. L.", journal = "Geophysical Research Letters", volume = "29", number = "14", pages = "Art. No. 1691", month = "July", year = "2002", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-135949010", note = "© 2002 American Geophysical Union. Received 7 June 2002; accepted 21 June 2002; published 25 July 2002. This work was supported by NSF grant EAR-9506377. We thank W. Panero and D. Andrault for kindly sharing their preprints with us, M. Long, P. Gelle and C. McCaughey for technical support and the reviewers for comments. Contribution No. 8865, Division of Geological and Planetary Sciences, California Institute of Technology. ", revision_no = "12", abstract = "Pure stishovite and coesite samples with zero porosity and dimensions appropriate for planar shock wave experiments have been synthesized with multi-anvil high-pressure techniques. The equation of state of stishovite is obtained by direct shock wave loading up to 235 GPa: K_(0T) = 306 ± 5 GPa and K'_(0T) = 5.0 ± 0.2 where K_(0T) and K'_(0T) are ambient bulk modulus and its pressure derivative, respectively. The Hugoniots (shock equations of state) for stishovite, coesite and quartz achieve widely differing internal energy states at equal volume and therefore allow us to determine the Gruneisen parameter of stishovite. On the basis of the resulting P-V-T equation of state for stishovite and previous studies on other phases on the MgO-SiO_2 binary, the breakdown reaction of MgSiO_3-perovskite to MgO and SiO_2 was calculated. Our calculations show that perovskite is thermodynamically stable relative to the stishovite and periclase assemblage at lower mantle conditions. We obtain similar results for a range of models, despite the appreciable differences among these experiment-based thermodynamic parameters.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33909, title ="Stishovite and its implications in geophysics: new results from shock-wave experiments and theoretical modeling", author = "Luo, S.-N. and Mosenfelder, J. L.", journal = "Physics-Uspekhi", volume = "45", number = "4", pages = "435-439", month = "April", year = "2002", issn = "1063-7869", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-113903468", note = "© 2002 Institute of Physics. Contribution No. 8856, Division of Geological and Planetary Sciences, California Institute of\nTechnology. ", revision_no = "19", abstract = "Abstract Unavailable.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/37937, title ="Analysis of hydrogen in olivine by SIMS: Evaluation of standards and protocol", author = "Mosenfelder, Jed L. and Le Voyer, Marion", journal = "American Mineralogist", volume = "96", number = "11-12", pages = "1725-1741", month = "November", year = "2001", doi = "10.2138/am.2011.3810", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130415-102910989", note = "© 2011 Mineralogical Society of America.\n\nManuscript received February 17, 2011; Manuscript accepted July 5, 2011; Manuscript handled by Florian Heidelbach.\n\nFinancial support for this research was provided by the Gordon and Betty Moore Foundation, the White Rose Foundation, and by NSF grant EAR-0947956 to George Rossman. We thank Erik Hauri, Jeremy Boyce, and Richard Hervig for helpful discussions; Chi Ma for assistance with the electron microprobe and SEM; and Jörg Hermann and an anonymous reviewer for helpful suggestions that improved the manuscript.", revision_no = "16", abstract = "We measured hydrogen concentrations in 12 olivines using secondary ion mass spectrometry (SIMS and NanoSIMS), cross-calibrated against Fourier transform infrared (FTIR) spectroscopy and nuclear reaction analysis (NRA). Five of these samples are routinely used for calibration in other laboratories. We assess the suitability of these olivines as standards based on over 300 SIMS analyses, comprising 22 separate calibrations. Seven olivines with 0–125 ppm H_(2)O give highly reproducible results; in contrast to previous studies, the data are fit to well-constrained calibration lines with high correlation coefficients (r^2 = 0.98–1). However, four kimberlitic megacrysts with 140–245 ppm H2O sometimes yield ^(16)O^(1)H/^(30)Si ratios that have low internal precision and can vary by up to a factor of two even in sequential analyses. A possible cause of this behavior is the presence of sub-microscopic inclusions of hydrous minerals, such as serpentine. In most cases, however, we link the anomalous results to the presence of sub-micrometer to micrometer-scale pores (as small as 100 nm), which we imaged using SEM and NanoSIMS. These pores are interpreted to be fluid inclusions containing liquid H_(2)O, other volatiles (including fluorine), and/or hydrous phase precipitates. Ionization of the contents of the pores contributes variably to the measured ^(16)O^(1)H, resulting in analyses with erratic depth profiles and corresponding high uncertainties (up to 16%, 2σ_mean). After filtering of these analyses using a simple criterion based on the error predicted by Poisson counting statistics, all the data fit well together. Our results imply that the Bell et al. (2003) calibration can be applied accurately to all olivines with IR bands from ~3400–3700 cm^(−1), without the need for band-specific IR absorption coefficients. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1463, title ="Calculation of Peridotite Partial Melting from Thermodynamic Models of Minerals and Melts, IV. Adiabatic Decompression and the Composition and Mean Properties of Mid-ocean Ridge Basalts", author = "Asimow, Paul D. and Hirschmann, M. M.", journal = "Journal of Petrology", volume = "42", number = "5", pages = "963-998", month = "May", year = "2001", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:ASIjpet01", note = "© Oxford University Press 2001. Reprinted with permission. \n\nReceived January 25, 2000; Revised typescript accepted August 16, 2000. \n\nThe authors gratefully acknowledge constructive reviews by Emily Klein, Jennifer Witter, and Kevin Johnson, and especially heroic editorial handling by Dennis Geist. P.D.A. was supported during part of this work by a postdoctoral research fellowship from Lamont–Doherty Earth Observatory. This work was supported by NSF grants OCE-9711735 to M.M.H., and EAR-9219899, OCE-9504517 and EAR-9706254 to E.M.S.", revision_no = "9", abstract = "Composition, mean pressure, mean melt fraction, and crustal thickness of model mid-ocean ridge basalts (MORBs) are calculated using MELTS. Polybaric, isentropic batch and fractional melts from ranges in source composition, potential temperature, and final melting pressure are integrated to represent idealized passive and active flow regimes. These MELTS-derived polybaric models are compared with other parameterizations; the results differ both in melt compositions, notably at small melt fractions, and in the solidus curve and melt productivity, as a result of the self-consistent energy balance in MELTS. MELTS predicts a maximum mean melt fraction (~0·08) and a limit to crustal thickness (<=15 km) for passive flow. For melting to the base of the crust, MELTS requires an ~200°C global potential temperature range to explain the range of oceanic crustal thickness; conversely, a global range of 60°C implies conductive cooling to ~50 km. Low near-solidus productivity means that any given crustal thickness requires higher initial pressure in MELTS than in other models. MELTS cannot at present be used to model details of MORB chemistry because of errors in the calibration, particularly Na partitioning. Source heterogeneity cannot explain either global or local Na–Fe systematics or the FeO–K2O/TiO2 correlation but can confound any extent of melting signal in CaO/Al2O3.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33766, title ="A model that reconciles major- and trace-element data from abyssal peridotites", author = "Asimow, Paul D.", journal = "Earth and Planetary Science Letters", volume = "169", number = "3-4", pages = "303-319", month = "June", year = "1999", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-110308922", note = "© 1999 Elsevier Science B.V.\nReceived 4 June 1998; revised version received 30 March 1999; accepted 30 March 1999.\nThis paper grew out of discussions with Charlie\nLangmuir, Ro Kinzler, and Marc Spiegelman.\nThanks to Charlie Langmuir for the use of his melting\nsoftware and fractionation calculations. Mike\nBaker and John Beckett kindly shared a preprint of\ntheir abyssal peridotite manuscript and gave permission\nto discuss their results in advance of publication.\nThe manuscript benefited from constructive reviews\nby Peter Kelemen and Rodey Batiza. The author is\nsupported by a postdoctoral research fellowship from\nLamont–Doherty Earth Observatory. [FA]", revision_no = "13", abstract = "Abyssal peridotite samples from slow-spreading oceanic ridges have been interpreted as residues of near-fractional melting processes on the basis of trace-element data, whereas major-element compositions and modes of the same samples require interactions between migrating melts and residual solids, either by equilibrium porous flow, refertilization, or olivine crystallization. Modeling of major- and trace-element data shows that these peridotite samples are consistent with a variety of melting and melt migration histories that include elements or episodes both of near-fractional melting and of equilibrium porous flow. A component of equilibrium porous flow explains peridotite compositions better than olivine deposition or refertilization. Mixing of primary basalt liquids composed of variable proportions of unmodified liquid increments extracted by near-fractional melting, and of liquids transported by equilibrium porous flow generates local trend systematics like those observed in fractionation-corrected basalt compositions at slow-spreading ridges. Both the local trend in basalts and the fractionated trace elements in peridotites are absent at the fast-spreading East Pacific Rise, allowing simpler models of melting and melt migration than those required at Atlantic and Indian ridges and implying a spreading-rate or magma-flux dependence to the mechanism of melt extraction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33409, title ="Calculation of Peridotite Partial Melting from Thermodynamic Models of Minerals and Melts. III. Controls on Isobaric Melt Production and the Effect of Water on Melt Production", author = "Hirschmann, M. M. and Asimow, Paul D.", journal = "Journal of Petrology", volume = "40", number = "5", pages = "831-851", month = "May", year = "1999", doi = "10.1093/petroj/40.5.831", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120821-130612151", note = "© 1999 Oxford University Press. \n\nReceived April 5, 1998; Accepted December 2, 1998. \n\nWe thank Bill Minarik, Glenn Gaetani, and Gautam Sen for thorough and constructive reviews. This work was supported by OCE-9711735 (M.M.H.), OCE-9529790 (M.S.G.) and EAR-9219899 and OCE-9504517 (E.M.S.). This paper is Caltech Division of Geological and Planetary Sciences Contribution 8510.\n\n", revision_no = "21", abstract = "We present a rigorous calculation of the isobaric entropy (S) change of the melting reaction for peridotite (∂S/∂F)^(rxn)_P, where F is the melt fraction. Calculations at 1 and 2 GPa for fertile and depleted peridotite show that (∂S/∂F)^(rxn)_P varies as a function of extent of melting, temperature, and residual mineral assemblage. Changes in reaction stoichiometry cause discontinuous changes in ∂S/∂F)^(rxn)_P. Although calculated (∂S/∂F)^(rxn)_P varies by about a factor of two (from ∼0.25 to ∼0.5 J/K per g), such variations have relatively little effect on the formation of melt during adiabatic upwelling and a characteristic value suitable for peridotite partial melting at least up to 3 GPa is 0.3 J/K per g. Calculated variations in isobaric melt productivity, (∂F/∂T)_P, are large and have a significant effect on calculated adiabatic productivity, (∂F/∂P)_S. For partial melting of fertile peridotite, MELTS calculations suggest that near-solidus productivities are greatly reduced relative to productivities at higher melt fraction, owing to the incompatible behavior of Na_(2)O and the effect of this component on the liquidus temperature of partial melts. This behavior can also be demonstrated in simple model systems. Calculated near-solidus productivity for fractional or incremental batch melting of peridotite is lower than for batch melting, but after a small amount of melting (∼2%), productivity for the fractional or incremental batch melting case is greater than that of batch melting. This too can be demonstrated both by MELTS calculations and by calculations in simple model systems. Productivities for systems enriched in incompatible components are systematically lower than those depleted in such components, though the total melt produced at any given temperature will be greater for an enriched system. Exhaustion of clinopyroxene from peridotite residua decreases calculated productivity by about a factor of four, and therefore extensive partial melting of harzburgitic residues is inhibited. Calculated isothermal addition of water to hot peridotite causes melting to increase roughly linearly with the abundance of water added to the system, in agreement with the trend recognized earlier for Mariana trough basalts. Melt production for calculated addition of a subduction fluid (45 wt % H_(2)O, 45% Na_(2)O, 10% K_(2)O) is only slightly greater than for pure water. If water addition to peridotite is not forced to be isothermal by an externally imposed heat sink or by buffering from low variance chemical reactions, then it will approach isenthalpic conditions, which will reduce melt production per increment of water added by about a factor of two. For heating of peridotite containing minor amounts of H_(2)O, calculations suggest that the extent of melting will remain small (<5%) until the temperature is sufficient to generate significant melt for an equivalent dry peridotite. Small degrees of melting deep in mantle source regions caused by alkalis, CO_2, and H_(2)O probably result in several distinct melting regimes where melt productivities are very small and melt compositions are strongly influenced by high concentrations of alkalis and/or volatiles. Such regions are almost certainly in the garnet peridotite stability field, and owing to the small extents of melting and low productivities in these deep melting zones, they are likely regions for development of extreme U-series disequilibria.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33408, title ="Steady-state Mantle–Melt Interactions in One Dimension: I. Equilibrium Transport and Melt Focusing", author = "Asimow, Paul D. and Stolper, E. M.", journal = "Journal of Petrology", volume = "40", number = "3", pages = "475-494", month = "March", year = "1999", doi = "10.1093/petroj/40.3.475", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120821-130330912", note = "© 1999 Oxford University Press. \n\nReceived December 1, 1997; accepted August 13, 1998. \n\nThe authors thank Tim Elliott, Peter Reiners and Marc Spiegelman for careful and thoughtful reviews, and Jon Davidson for editorial handling. John Longhi kindly performed some calculations for us with his melting model. We have had numerous helpful discussions with Peter Kelemen and Marc Spiegelman. This work was supported by NSF Grants OCE-9529878 and EAR 9219899, and by a Lamont–Doherty Earth Observatory postdoctoral fellowship to P.D.A. This is Caltech Division of Geological and Planetary Sciences Contribution 8508.", revision_no = "17", abstract = "Mantle–melt interaction during melt transport is explored in one dimension and steady state. We reconsider the equivalence between one-dimensional steady equilibrium transport and batch melting. In the absence of diffusion and radioactivity, conservation of mass flux requires that the major and trace element compositions of melt and solid at each point are the same as is generated by batch melting the source composition at the same pressure and temperature. Energy conservation requires that temperature and extent of melting are independent of melt migration except for irreversible source terms related to viscous compaction and gravitational energy release. The equivalence of phase compositions at each pressure between steady-state equilibrium transport and batch melting simplifies melt transport calculations. We examine the effects of increasing the melt flux to simulate melt focusing by channeling or by two-dimensional flow with converging melt streamlines. Melt focusing modifies the mineralogy of both residual matrix and erupted melt. We use MELTS calculations to model the formation of dunite by this mechanism and quantify the melt flux required to exhaust orthopyroxene from the residue as a function of pressure. The model dunites are found to be similar to natural dunites observed in the mantle section of ophiolite sequences.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39532, title ="Melting the Mantle", author = "Asimow, Paul D.", pages = "55-68", month = "January", year = "1999", isbn = "9780126431407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130723-130553608", note = "© 2000 Academic Press.", revision_no = "14", abstract = "The stony part of the Earth is solid under normal conditions\nat the present day. Volcanism is the eruption of\nmolten or partially molten rock, that is, magma. The\nfirst stage of any volcanic process therefore must be\nmelting: We have to produce a liquid by partial melting\nbefore it can migrate from the source region (see Migration\nof Melt chapter) and subsequently erupt (Part II).\nThe locations of volcanoes on Earth are controlled primarily\nby where melting takes place. The volume, frequency,\nand style of eruptions are dependent on many\nfactors but the first considerations are how much magma\nis supplied by melting, at what depth melting takes place, and the distribution of melt production in the source\nregion in space and time.\n\n\nBefore roughly 1960, igneous petrology was mostly\nconcerned with the evolution and differentiation of\nmagma after it left its source region. In the following\ntwo decades, attention shifted to the pressure (P) and\ntemperature (T) at which primary melts were extracted\nfrom the mantle, without detailed understanding of how\nthe melts were produced. In the last 20 years, however,\nthe application of ideas from thermodynamics, experimental\npetrology, and fluid dynamics has provided a\nstrong basis for understanding the basic physical processes\nunderlying the melting of Earth's mantle. This\nchapter explores how and why the crust and mantle of\nthe Earth melt, which together with information about\ntectonic processes and chemical composition (discussed\nin other chapters in this part) determines where and when\nmelting takes place.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33711, title ="Algorithmic modifications extending MELTS to calculate subsolidus phase relations", author = "Ghiorso, Mark S. and Asimow, Paul D.", journal = "American Mineralogist", volume = "83", number = "9-10", pages = "1127-1132", month = "September", year = "1998", issn = "0003-004X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-132227508", note = "© 1998 Mineralogical Society of America.\n\nManuscript received: April 13, 1998; manuscript accepted: June 10, 1998; paper handled by David M. Jenkins.\n\nThe authors thank Denton Ebel, Alex Navrotsky, and Tracy Rushmer for helpful comments on the manuscript, and David Jenkins for editorial handling. Paul D. Asimow is supported by a postdoctoral research fellowship from Lamont-Doherty Earth Observatory. M.S.G. acknowledges material support from the National Science Foundation (OCE-9529790).", revision_no = "17", abstract = "Algorithmic modifications to the MELTS software package are presented in order that calculations of heterogeneous phase equilibria can be performed in the subsolidus. Methods\nare presented for: (1) selecting an \"initial guess assemblage\" that satisfies the bulk composition constraints; (2) detecting saturation of new phases (including liquid) in an assemblage; (3) adding and removing phases from the assemblage without adjusting the system bulk composition; and (4) constraining the assemblage to a fixed f_(O2). These methods have O2 been added to MELTS, allowing it to calculate heterogeneous phase equilibria with or without liquid, closed or open to O, and with fixed intensive variables (P,T), (P,S), (P,H), or (V,T). Applications include fractional melting calculations, metamorphic phase equilibria, and geophysical models of subsolidus regions of the Earth.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33480, title ="Determination of the partial molar volume of SiO_2 in silicate liquids at elevated pressures and temperatures: A new experimental approach", author = "Gaetani, Glenn A, and Stolper, Edward M.", journal = "Geochimica et Cosmochimica Acta", volume = "62", number = "14", pages = "2499-2508", month = "July", year = "1998", doi = "10.1016/S0016-7037(98)00172-0", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120823-104105677", note = "© 1998 Elsevier Science Ltd. \n\nReceived 4 August 1997. Revised 20 April 1998. Accepted 20 April 1998. Available online 21 November 1998. \n\nThe authors thank R. Lange, A. Navrotsky, and an anonymous referee for helpful reviews. The comments of Y. Bottinga and T. Grove are also gratefully acknowledged. The authors thank S. Newman for performing FTIR analyses of Glass Buttes rhyolite. This research was supported by DOE grant DE-FG03-85ER13445, by NSF grant EAR-9725461, and by an O. K. Earl prize postdoctoral fellowship (to GG) from the Division of Geological and Planetary Sciences at the California Institute of Technology. Caltech Division of Geological and\nPlanetary Sciences Contribution 5707.", revision_no = "16", abstract = "This study presents a new approach for determining the partial molar volume and its pressure derivative for a silicate liquid component through an experimental determination of the isothermal pressure dependence of the solubility in the liquid of a crystalline phase having the composition of the component. Because this approach allows the determination of partial molar volumes of liquid components at elevated pressure, it has the potential to detect pressure-induced structural changes associated with particular components in silicate liquid through their influence on partial molar volumes. To illustrate the approach, an experimental determination of the solubility of quartz in a rhyolitic liquid was used to determine the partial molar volume of SiO_2 at pressures up to 35 kbar and a temperature of 1350°C. The 1 bar partial molar volume for SiO_2 determined in this way, 2.635 ± 0.009 J/bar, is slightly smaller than the 2.690 ± 0.006 J/bar determined by Lange and Carmichael (1987) (all uncertainties are 1σ). The isothermal pressure dependence of the partial molar volume of SiO_2 at 10 to 35 kbar (−8.69 × 10^(−6) ± 6.1 × 10^(−7) J/bar^2) is approximately one-half of the value determined by Kress and Carmichael (1991) at 1 bar (−1.96 × 10^(−5) ± 0.2 × 10^(−6) J/bar^2). Our high pressure determination can be reconciled with the existing 1 bar volume and compressibility data if the isothermal pressure dependence of the partial molar volume of SiO_2 in silicate liquids decreases rapidly between 1 bar and 10 kbar, then remains approximately constant to at least 35 kbar.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33612, title ="Calculation of Peridotite Partial Melting from Thermodynamic Models of Minerals and Melts. I. Review of Methods and Comparison with Experiments", author = "Asimow, Paul D. and Hirschmann, M. M.", journal = "Journal of Petrology", volume = "39", number = "6", pages = "1091-1115", month = "June", year = "1998", doi = "10.1093/petrology/39.6.1091", issn = "0022-3530", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-115542189", note = "© 1998 Oxford University Press. \n\nReceived May 9 1997; revised typescript accepted December 12. 1997. \n\nThis work was supported by OCE-9711735 (M.M.H.), OCE-9529790 (M.S.G.), and EAR-9219899 and OCE-9504517 (E.M.S.). This work benefited greatly from discussions with Mike Baker, John Beckett and Sally Newman, and from helpful reviews by Rebecca Lange, Gautam Sen and Ro Kinzler. This paper is Caltech Division of Geological and Planetary Sciences Contribution 6836.", revision_no = "17", abstract = "Thermodynamic calculation of partial melting of peridotite using the MELTS algorithm has the potential to aid understanding of a wide range of problems related to mantle melting. We review the methodology of MELTS calculations with special emphasis on the features that are relevant for evaluating the suitability of this thermodynamic model for simulations of mantle melting. Comparison of MELTS calculations with well–characterized peridotite partial melting experiments allows detailed evaluation of the strengths and weaknesses of the algorithm for application to peridotite melting problems. Calculated liquid compositions for partial melting of fertile and depleted peridotite show good agreement with experimental trends for all oxides; for some oxides the agreement between the calculated and experimental concentrations is almost perfect, whereas for others, the trends with melt fraction are comparable, but there is a systematic offset in absolute concentration. Of particular interest is the prediction by MELTS that at 1 GPa, near–solidus partial melts of fertile peridotite have markedly higher SiO_2 than higher melt fraction liquids, but that at similar melt fractions, calculated partial melts of depleted peridotites are not SiO_2 enriched. Similarly, MELTS calculations suggest that near–solidus partial melts of fertile peridotite, but not those of depleted peridotite, have less TiO_2 than would be anticipated from higher temperature experiments. Because both experiments and calculations suggest that these unusual near–solidus melt compositions occur for fertile peridotite but not for depleted peridotite, it is highly unlikely that these effects are the consequence of experimental or model artifacts. Despite these successes of the results of calculations of peridotite melting using MELTS, there are a number of shortcomings to application of this thermodynamic model to calculations of mantle melting. In particular, calculated compositions of liquids produced by partial melting of peridotite have more MgO and less SiO_2 than equivalent experimentally derived liquids. This mismatch, which is caused by overprediction of the stability of orthopyroxene relative to olivine, causes a number of other problems, including calculated temperatures of melting that are too high. Secondarily, the calculated distribution of Na between pyroxenes and liquid does not match experimentally observed values, which leads to exaggerated calculated Na concentrations for near–solidus partial melts of peridotite. Calculations of small increments of batch melting followed by melt removal predict that fractional melting is less productive than batch melting near the solidus, where the composition of the liquid is changing rapidly, but that once the composition of the liquid ceases to change rapidly, fractional and batch melting produce liquid at similar rates per increment of temperature increase until the exhaustion of clinopyroxene. This predicted effect is corroborated by sequential incremental batch melting experiments (Hirose & Kawamura, 1994, Geophysical Research Letters, 21, 2139–2142). For melting of peridotite in response to fluxing with water, the calculated effect is that melt fraction increases linearly with the amount of water added until exhaustion of clinopyroxene (cpx), at which point the proportion of melt created per increment of water added decreases. Between the solidus and exhaustion of cpx, the amount of melt generated per increment of water added increases with temperature. These trends are similar to those documented experimentally by Hirose & Kawamoto (1995, Earth and Planetary Science Letters, 133, 463–473).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33376, title ="An analysis of variations in isentropic melt productivity", author = "Asimow, Paul D. and Hirschmann, M. M.", journal = "Philosophical Transactions A: Mathematical, Physical and Engineering Sciences", volume = "355", number = "1723", pages = "255-281", month = "February", year = "1997", doi = "10.1098/rsta.1997.0009", issn = "1364-503X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120820-160120936", note = "© 1997 The Royal Society. \n\nThe authors are grateful to Mark Ghiorso and Richard Sack, the authors of MELTS, for permission to play with their code and suit it to our needs. Mike O'Hara provided a helpful review and much important devil's advocacy. This work was supported by NSF grants OCE-9504517, EAR-9219899 and OCE-9314505. This is Division of Geological and Planetary Sciences contribution 5703.", revision_no = "18", abstract = "The amount of melt generated per unit pressure drop during adiabatic upwelling, the isentropic melt productivity, cannot be determined directly from experiments and is commonly assumed to be constant or to decrease as melting progresses. From analysis of one– and two–component systems and from calculations based on a thermodynamic model of peridotite partial melting, we show that productivity for reversible adiabatic (i.e. isentropic) depressurization melting is never constant; rather, productivity tends to increase as melting proceeds. Even in a one–component system with a univariant solid–liquid boundary, the 1/T dependence of (∂S/∂T)_P and the downward curvature of the solidus (due to greater compressibility of liquids relative to minerals) lead to increased productivity with increasing melt fraction during batch fusion (and even for fractional fusion in some cases). Similarly, for multicomponent systems, downward curvature of contours of equal melt fraction between the solidus and the liquidus contributes to an increase in productivity as melting proceeds. In multicomponent systems, there is also a lever–rule relationship between productivity and the compositions of coexisting liquid and residue such that productivity is inversely related to the compositional distance between coexisting bulk solid and liquid. For most geologically relevant cases, this quantity decreases during progressive melting, again contributing to an increase in productivity with increasing melting. These results all suggest that the increases in productivity with increasing melt fraction (punctuated by drops in productivity upon exhaustion of each phase from the residue) predicted by thermodynamic modelling of melting of typical mantle peridotites using MELTS are neither artifacts nor unique properties of the model, but rather general consequences of adiabatic melting of upwelling mantle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33405, title ="The effect of pressure-induced solid-solid phase transitions on decompression melting of the mantle", author = "Asimow, Paul D. and Hirschmann, M. M.", journal = "Geochimica et Cosmochimica Acta", volume = "59", number = "21", pages = "4489-4506", month = "November", year = "1995", doi = "10.1016/0016-7037(95)00252-U", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120821-120111971", note = "© 1995 Elsevier Science Ltd. \n\nReceived 19 January 1995. Accepted 10 July 1995. Available online 5 April 2000. \n\nP. D. Asimow was supported by an NSF graduate fellowship. M.M. Hirschmann was supported by an NSF Earth Sciences post-doctoral fellowship. This paper is based in part on work funded by NSF grants EAR-92-19899 and OCE-93-14505. We are grateful to Frank Richter and Peter Kelemen for helpful reviews and to Reid Cooper for useful discussions. Division of Geological and Planetary Sciences Contribution #5499. \n\nEditorial handling: E. Merino", revision_no = "23", abstract = "Pressure-release melting of the earth's mantle is thought to be an isentropic process. The intersection of an isentropic melting path with a solid-state phase transition affecting the residual minerals must result in some change in melting rate unless the entropy of reaction of the phase transition is exactly zero. Furthermore, both phase transitions of primary interest for peridotite melting in the upper mantle (garnet-spinel peridotite and spinel-plagioclase peridotite) have positive Clapeyron slopes, and hence the lower-pressure assemblage has a higher molar entropy. Thus, these phase transitions must retard isentropic, decompression melting, or even lead to freezing. There cannot be enhanced melting accompanying such phase transitions, even if there is a cusp in the solidus.\nModel calculations in simple one-component and two-component systems demonstrate the effect of solid-solid phase transformations on isentropic decompression melting. Conversion of low entropy solids to high entropy solids in the presence of liquid results in crystallization; the amount of crystallization depends on the relative molar entropies of the solid and liquid phases, on the modal abundance of the reacting solid phases, and on the proportion of liquid present when the reaction is initiated. The effect of solid-solid phase transitions on freezing is more pronounced for fractional fusion than for batch fusion in that melting ceases for a finite pressure interval at pressures below the invariant point where melt and the solids involved in the phase transition coexist.\nIsentropic upwelling calculations for a model nine-component peridotite using a modified version of the MELTS potential minimization algorithm (Ghiorso et al., 1994; Ghiorso and Sack, 1995) verify that the simple-system behavior can be extended to multicomponent, mantle-like systems: melt production is suppressed during the transformation from garnet to spinel peridotite and for batch melting there is freezing during the transformation from spinel to plagioclase peridotite; these effects are exaggerated during fractional fusion and barren zones are produced as in the simple systems. These results imply that melt production during upwelling may be highly nonuniform. Very slow melt production in the spinel-garnet transition region may enhance development of U-Th disequilibria. If significant contributions of melt from garnet peridotite are needed to account for the Lu-Hf systematics and REE patterns in MORB, melting must begin deep within the garnet stability zone. If plagioclase ever appears in the melting residue, this event is likely to end decompression melting despite further upwelling. Regions such as the garnet-spinel and spinel-plagioclase peridotite transitions may serve as nucleation sites for solitary waves in porous flow or regions of fracture formation and enhanced melt segregation.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/65614, title ="Isentropic Melting Processes in the Mantle", author = "Asimow, P. D. and Hirschmann, M. M.", number = "3/95", pages = "12-14", month = "July", year = "1995", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160323-093201156", note = "© 1995 Alfred-Wegener-Stiftung.", revision_no = "10", abstract = "Batch melting of ascending mantle can be approximated as an isentropic\nprocess, since on the time scale of melting heat flow into or out of source\nregions will typically be negligible and the process is slow enough to be close to\nreversible. Similarly, fractional fusion can be idealized as a series of\nincremental isentropic melting steps, although the entropy of the residue\ndecreases in each step. Although actual melting processes (e.g., involving melt\nmigration, diffusion, and convective boundary layers) must deviate to some\nextent from idealized isentropic conditions, modeling of mantle processes under\nthe assumption of constant entropy is tractable from a thermodynamic\nperspective and leads to a number of insights. Here we present models of the\nproductivity of isentropic pressure-release melting, consider the effect of solid-solid\nphase transitions on melting, and model deep crystal fractionation in\nascending melts of the mantle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33845, title ="Fluid Outflows From Venus Impact Craters: Analysis From Magellan Data", author = "Asimow, Paul D. and Wood, John A.", journal = "Journal of Geophysical Research E", volume = "97", number = "E8", pages = "13643-13665", month = "August", year = "1992", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120905-082050979", note = "© 1992 by the American Geophysical Union. Received 1 October 1991; accepted 28 April 1992. The authors wish to thank Brennan Klose, Akihiko Hasimoto, Beth Holmberg, Craig Leff, and Peter Schultz for discussions and technical help. We are indebted to Phillip Shaller and Robert Herrick for providing unpublished data. This work was supported by JPL contract 958593.", revision_no = "15", abstract = "Many impact craters on Venus have unusual outflow features originating in or under the continuous ejecta blankets and continuing downhill into the surrounding terrain. These features clearly resulted from flow of low-viscosity fluids, but the identity of those fluids is not clear. In particular, it should not be assumed a priori that the fluid is an impact melt. A number of candidate processes by which impact events might generate the observed features are considered, and predictions are made concerning the rheological character of flows produced by each mechanism. A sample of outflows was analyzed using Magellan images and a model of unconstrained Bingham plastic flow on inclined planes, leading to estimates of viscosity and yield strength for the flow materials. It is argued that at least two different mechanisms have produced outflows on Venus: an erosive, channel-forming process and a depositional process. The erosive fluid is probably an impact melt, but the depositional fluid may consist of fluidized solid debris, vaporized material, and/or melt. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33908, title ="Tests of random density models of terrestrial planets", author = "Kaula, William M. and Asimow, Paul D.", journal = "Geophysical Research Letters", volume = "18", number = "5", pages = "909-912", month = "May", year = "1991", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120906-111842591", note = "© 1991 American Geophysical Union. Received 25 July 1990; Revised October 18, 1990; accepted 20 October 1990. Paul Asimow was supported for a visit to U.C.L.A. by the NASA\nPlanetary Geology and Geophysics Undergraduate Research Program. ", revision_no = "13", abstract = "Random density models are analyzed to determine the low degree harmonics of the gravity field of a planet, and therefrom two properties: an axiality P_l , the percent of the degree variance in the zonal term referred to an axis through the maximum for degree l; and an angularity E_(ln) , the angle between the maxima for two degrees l, n. The random density distributions give solutions reasonably consistent with the axialities and angularities for the low degrees, l < 5, of Earth, Venus, and Moon, but not for Mars, which has improbably large axialities and small angularities. Hence the random density model is an unreliable predictor for the non‐hydrostatic second‐degree gravity of Mars, and thus for the moment‐of‐inertia, which is more plausibly close to 0.365MR^2.", }