[
{
"id": "authors:m1nv9-5xx14",
"collection": "authors",
"collection_id": "m1nv9-5xx14",
"cite_using_url": "https://authors.library.caltech.edu/records/m1nv9-5xx14",
"type": "article",
"title": "Shallow Differentiation of Primitive Arc Magmas at the Jurassic Emigrant Gap Mafic Complex, Sierra Nevada, California",
"author": [
{
"family_name": "Ryan-Davis",
"given_name": "Juliet",
"orcid": "0000-0001-7048-5937",
"clpid": "Ryan-Davis-Juliet"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0003-3252-7109",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Sisson",
"given_name": "Thomas W",
"orcid": "0000-0003-3380-6425"
}
],
"abstract": "The Emigrant Gap composite pluton exposes ultramafic to silicic intrusive rocks that preserve the chemical evolution of primitive mafic arc magmas and their open-system interactions in the upper crust during mid-Jurassic growth of the Sierra Nevada batholith (California). We present field and petrographic observations and mineral and whole-rock chemistry of the ~35-km2 ultramafic to dioritic Emigrant Gap mafic complex and an adjacent penecontemporaneous ~90-km2 granodiorite that together make up the composite pluton. In the Emigrant Gap mafic complex, four roughly central masses of dunite, wehrlite, and olivine clinopyroxenite are surrounded by weakly layered gabbronorite and non-layered diorite. The ultramafic rocks are cumulates formed from near-liquidus minerals of primitive arc magmas that accumulated in steep feeder zones with substantial modification by melt–mush reaction as primitive liquids repeatedly transited the mush-filled conduits. The dominant gabbronoritic rocks are the variably accumulative products of more advanced crystallization–differentiation of arc tholeiitic basalts and basaltic andesites. The adjacent granodiorite intrusion originated separately and preserves field and geochemical evidence for assimilation of metasedimentary rocks. Open-system hybridization between the gabbronoritic mushes and the granodioritic magma produced an intervening body of two-pyroxene diorite. We infer that the ultramafic rocks and gabbronorite of the Emigrant Gap mafic complex crystallized from near-primitive arc basaltic to basaltic andesitic magmas at ~0.15–0.3 GPa, with estimated fO2 of ≥FMQ +1 and dissolved H2O concentrations of only ~0.5–2 wt %. Notably, the Emigrant Gap composite pluton is distinct from other Mesozoic plutons in the Sierra Nevada batholith because of (1) its abundance of mafic and ultramafic rocks that crystallized from relatively primitive mafic melts and (2) the low inferred H2O concentrations of its parental magmas, indicated by a near absence of igneous amphibole and by the intermediate rather than calcic compositions of plagioclase. A Jurassic regional extension event probably accounts for the formation of relatively dry primitive arc magmas, as well as for their ascending to the upper crust.
",
"doi": "10.1093/petrology/egag013",
"issn": "0022-3530",
"publisher": "Oxford University Press (OUP)",
"publication": "Journal of Petrology",
"publication_date": "2026-02",
"series_number": "2",
"volume": "67",
"issue": "2",
"pages": "egag013"
},
{
"id": "authors:y42cq-mh835",
"collection": "authors",
"collection_id": "y42cq-mh835",
"cite_using_url": "https://authors.library.caltech.edu/records/y42cq-mh835",
"type": "article",
"title": "Temporal variation in oxygen isotopes of peraluminous granites derived from sedimentary sources",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Hern\u00e1ndez-Montenegro",
"given_name": "Juan D.",
"orcid": "0000-0001-7505-4650",
"clpid": "Hern\u00e1ndez-Montenegro-Juan-D"
}
],
"abstract": "\n
\n
\n
The oxygen isotopic composition of magmatic rocks provides critical constraints on the contributions of crust versus mantle in their genesis. Peraluminous granites derived from partial melting of sedimentary rocks offer a unique archive to examine how the oxygen isotope composition of sedimentary rocks recycled into magmas has changed throughout Earth history. In this study, we explore this record through a two-pronged approach. First, we compile a comprehensive dataset of oxygen isotope bulk-rock and mineral analyses from globally distributed peraluminous granites and volcanic rocks ranging in age from 3.2 billion years to 6 million years. Second, we model the isotopic fractionation between sedimentary source rocks and derivative melts, as well as minerals in equilibrium with the melt during anatexis. Our compilation demonstrates a progressive increase in δ18O values of zircon and garnet from the Archean to Paleoproterozoic and again in the latest Neoproterozoic to Phanerozoic. Specifically, the average δ18O of zircon from peraluminous granites increases from 6.7 ± 1.0 ‰ to 9.5 ± 0.8 ‰ at ∼ 2.35 Ga, followed by another increase to 10.4 ± 0.7 ‰ after 600 Ma (errors are ± 1 s.d.). These observations align with the sedimentary rock record which suggests enhanced weathering and clay deposition resulting from tectonic and biological forcings. Furthermore, the increase in δ18O of peraluminous granites broadly mirrors similar secular increases in the δ18O values of siliciclastic sedimentary rocks. However, using our modeled fractionations between melt and source rock, the reconstructed source-rock δ18O values capture only the lower end of the siliciclastic sedimentary rock range, suggesting that sedimentary rocks recycled into magmas have, on average, lower δ18O values than coeval clay-rich shales. We propose that any global analyses of oxygen isotopes in magmatic rocks or zircon should use the average values of calculated source rocks for peraluminous granites in defining crustal contributions. Furthermore, our study highlights the broader implications of the observed trends, including the progressive contamination of the mantle and elevation of its δ18O values.
\n
\n
\n
\n
\n
\n
Lower-crustal garnet clinopyroxenite (sometimes termed “arclogite”) fractionation in thick-crustal (>35 km) arc settings presents a compelling model to explain Fe-depletion trends, high oxygen fugacity, and evidence of recent delamination observed in many continental arcs. However, the origin of the garnet clinopyroxenites via igneous or metamorphic processes remains unclear. Due to the preferential incorporation of light Fe isotopes in garnet relative to clinopyroxene or amphibole, Fe isotopes are ideally suited for studying the effects of garnet fractionation on magmatic systems. Here, we present whole-rock and mineral Fe isotope data from a suite of lower to mid/upper-crustal Andean xenoliths from Mercaderes, Colombia. This data is combined with petrography, major and trace element mineral and whole-rock chemistry, geothermobarometry, and thermodynamic modeling to explore the xenoliths' petrogenesis and the Northern Andes' crustal structure. Whole-rock samples display a narrow range of Fe isotope compositions (δ56Fe = –0.02 to +0.11 ‰), which do not correlate with lithology, chemistry, or pressure-temperature conditions. This result is inconsistent with previous studies predicting the existence of an isotopically light Fe reservoir in the garnet-rich lower Andean crust. Through thermodynamic modeling, we show that the lack of isotopic fractionation in the Mercaderes xenoliths is more consistent with the suite representing a prograde metamorphic sequence, in which amphibole dehydration reactions drive metamorphism of mid/upper-crustal diorite protoliths. While our data do not preclude the presence of garnet clinopyroxenite cumulates at the base of the Andean crust, or that the delamination of such cumulates played an important role in the evolution of the Andes, they do indicate that not all garnet clinopyroxenites are cumulate in origin. Instead, the lower Andean crust represents an amalgamation of igneous and metamorphic rock, with metamorphism of mid-crustal lithologies and partial melting of mafic cumulate roots acting in tandem to drive densification and delamination of the lower crust in a self-feeding mechanism.
\n
\n
\n
\n
\n
\n
Granites are an important compositional endmember and critical building block of the continental crust. Yet, their origin remains controversial primarily due to the diversity of granite types demanding different formation processes and sources. This chapter reviews the geochemical features of four broad categories of granites (strongly peraluminous granites, arc-related granites, post-collisional metaluminous, magnesian potassic granites, and ferroan granites) and their inferred modes of origin and distribution through time. Stable isotopes including traditional (O and S) and non-traditional (Si, Fe, and Ti) are highlighted as tools to understand differentiation of basalts and crustal assimilation during granite formation.
\n
\n
\n
\n
\n
\n
The large variability in Fe isotope ratios of sedimentary rocks (particularly those from the Archean and Proterozoic) contrasts with that of igneous rocks, which display a much more limited range in values. Notably, among igneous rocks, those inferred to form via partial melting of siliciclastic sediments – strongly peraluminous granites (SPGs) – exhibit greater variability in their Fe isotope compositions, suggesting SPGs may capture isotopic variations in the sedimentary record. However, the extent and mechanisms of iron isotope fractionation between SPGs and their source remain poorly understood. Our study integrates iron isotope analyses with petrological modeling to investigate equilibrium isotopic fractionation during generation of SPG magmas. As a case study, we focus on the Neoarchean Ghost Lake Batholith and the adjacent metasedimentary rocks in Ontario, Canada. These units represent an internally differentiated SPG batholith and metamorphosed sedimentary rocks interpreted as the source of the batholith.
\n
We measured δ56Fe compositions of SPG samples, metasedimentary rocks, and a restitic rock. Sulfide grains were also measured in four metapelite samples and a granite sample. We find no correlation between the δ56Fe composition of metasedimentary rocks and their metamorphic grade, indicating iron isotopes behave as a closed system during metamorphism. Modeling results show that iron isotopes in SPGs from the Ghost Lake batholith are consistent with equilibrium fractionation during biotite dehydration melting, with predicted δ56Fe values for melts and restitic assemblages mainly controlled by the source composition. Our results predict negligible isotopic fractionation between the residue and the source, whereas ∼0.177–0.277 ‰ is expected between SPG melts and the residue, accounting for high δ56Fe values in granite samples. Lower δ56Fe values may indicate that some granites represent mixtures of melt and cumulus material or result from assimilation of restite or source/host rock. However, despite deviations from pure equilibrium fractionation, the variability in δ56Fe values for SPGs is about one order of magnitude smaller than that seen in the sedimentary record for the Archean and Proterozoic (∼0.2 ‰ vs. >2 ‰). We posit that this narrower range of isotopic variation in SPGs results from metamorphism and partial melting, which can homogenize large isotopic variations in sedimentary protoliths. Thus, SPGs represent reliable archives for the bulk iron isotope evolution of siliciclastic sedimentary rocks through time.
\n
\n
\n
\n
\n
We present bulk-rock and mineral Fe isotope data of ultramafic to mafic xenoliths and basaltic to andesitic lavas from Adagdak Volcano (Adak Island, Central Aleutians) to study the effects of early differentiation on the Fe isotopic evolution of island arc basalts and their crystallization products. The Fe isotope composition of ultramafic cumulate xenoliths increases from dunite (δ56Fe = –0.09 to –0.02 ‰) to clinopyroxenite (δ56Fe = +0.06 to +0.09 ‰), consistent with higher modal proportions of clinopyroxene (δ56Fe = –0.05 to +0.11 ‰) relative to olivine (δ56Fe = –0.10 to +0.06 ‰) in the latter. Mid-crustal cumulate amphibole gabbro and hornblendite cumulates also record heavier Fe isotope compositions (δ56Fe = +0.04 to +0.08 ‰) due to the abundance of isotopically heavy amphibole (δ56Fe = +0.07 to +0.09 ‰) and magnetite (δ56Fe = +0.11 to +0.13 ‰) in these rocks. High inter-mineral fractionations observed in spinel-olivine and spinel-clinopyroxene pairs (Δ56Fespl-ol = +0.12 to +0.28 and Δ56Fespl-cpx = +0.06 to +0.19) suggest that spinel is not recording equilibrium crystallization conditions for the ultramafic assemblages, likely due to subsolidus Fe-Mg exchange. Our data also include Fe isotope measurements of one mantle dunite (δ56Fe = +0.03 ± 0.05 ‰). Five Adagdak lavas, spanning from basalts to andesites, yield a narrow range of δ56Fe between +0.03 and +0.06 ‰. Our results highlight the potential of amphibole in driving the Fe isotope depletion trends observed in many erupted arc lavas, as amphibole hosts 28–99 % of the FeOT budget in the amphibole gabbro and hornblendite cumulates. This is also supported by single-crystal synchrotron Mössbauer spectroscopy of two amphibole grains, the first from an amphibole gabbro and the second from a hornblendite, which yield Fe3+/ΣFe ratios of 0.55 ± 0.06 and 0.58 ± 0.02, respectively. Water content and hydrogen isotope compositions determined by secondary-ion mass spectrometry from the same amphibole grains indicate partial dehydrogenation. Using Rayleigh fractionation modeling to account for oxidation during post-crystallization dehydrogenation, we calculate magmatic Fe3+/ΣFe ratios of 0.41 ± 0.04 for the amphibole gabbro and 0.30 ± 0.05 for the hornblendite. These data are then used to estimate an appropriate Fe force constant for Adagdak amphibole and quantitatively evaluate the effects of amphibole fractionation. Through a fractional crystallization model, we show how arc melts may experience periods of increasing δ56Fe during olivine-dominated fractionation, followed by decreasing δ56Fe once magnetite and amphibole saturate as cumulate phases. Notably, this dichotomy between fractionation of isotopically light versus heavy cumulate assemblages and its effects on the Fe isotope evolution of arc magmas is not captured by the Adagdak lava record, highlighting the utility of cumulates in chronicling the early isotopic evolution of magmatic systems.
\n
\n
\n\n\n
Contributions of heat and/or mass from mafic magmas are commonly invoked in models of voluminous granodiorite and andesite generation in magmatic and volcanic arcs worldwide. However, mafic intrusions are a volumetrically minor component in most arc batholiths. This is the case in the Sierra Nevada batholith, California, USA, where gabbro and diorite plutons are smaller and less abundant than the granitoid suites that make up the bulk of the batholith. Here, we constrain the timing and geochemistry of mafic intrusions in the Sierra Nevada batholith to assess the role of these compositions in arc batholith construction. Previous detailed studies on a limited number of mafic intrusions demonstrate that they formed penecontemporaneously with the felsic batholith, but there is a need for a broader survey of mafic plutons using modern geochronological techniques. New U-Pb zircon ages for 13 gabbro to diorite plutons and geochemistry from 17 mafic intrusions in the eastern Sierra Nevada batholith document two main episodes of mafic magmatism in the eastern Sierra Nevada batholith, from 168 Ma to 145 Ma and from 100 Ma to 89 Ma. These episodes overlap with the ages of granitoid plutons in the eastern Sierra Nevada batholith, including the Late Jurassic Palisade Crest and Late Cretaceous John Muir intrusive suites, in addition to other felsic plutons dated in the eastern Sierra Nevada batholith. Non-primitive mineral compositions in the mafic bodies indicate that their parental magmas are the evolved products of mantle-derived basalts that first differentiated in the lower crust prior to ascent and crystallization in the upper crust. The presence of rocks with cumulate textures, as well as a wide range of bulk-rock compositions (SiO2 wt% 38–64, Mg# 39–74), show that magmatic differentiation continued within each mafic body after intrusion into the upper crust. Sr/Y ratios in melt-like (i.e., non-cumulate) mafic samples suggest that the crustal thickness of the Sierra Nevada batholith was roughly 30 km in the Early Jurassic and increased to ~44 km by the Late Cretaceous. Concomitant intrusion of mafic melts along with voluminous granitoid plutons supports mantle melting as a major contributor of heat and magmatic volumes to the crust during construction of the eastern Sierra Nevada batholith.
\n\n
Strongly peraluminous granites (SPGs) are generated by the partial melting of sedimentary rocks and can thus provide a novel archive to reveal secular trends in Earth's environmental history that integrate siliciclastic sedimentary lithologies. The nitrogen (N) content of Archean, Proterozoic, and Phanerozoic SPGs reveals a systematic increase across the Precambrian–Phanerozoic boundary. This rise is supported by a coeval increase in the phosphorus (P) contents of SPGs. Collectively, these data are most parsimoniously explained by an absolute increase in biomass burial in the late Proterozoic or early Phanerozoic by a factor of ~5 and as much as 8. The Precambrian–Phanerozoic transition was a time of progressive oxygenation of surface environments paired with major biological innovations, including the rise of eukaryotic algae to ecological dominance. Because oxygenation suppresses biomass preservation in sediments, the increase in net biomass burial preserved in SPGs reveals an expansion of the biosphere and an increase in primary production across this interval.
",
"doi": "10.1130/g51800.1",
"issn": "0091-7613",
"publisher": "Geological Society of America",
"publication": "Geology",
"publication_date": "2024-01-01",
"series_number": "1",
"volume": "52",
"issue": "1",
"pages": "87-91"
},
{
"id": "authors:h7w1g-b4n12",
"collection": "authors",
"collection_id": "h7w1g-b4n12",
"cite_using_url": "https://authors.library.caltech.edu/records/h7w1g-b4n12",
"type": "article",
"title": "Carbonate clumped isotopes record the heterogenous onset of metamorphism in the Alta stock contact aureole, Utah",
"author": [
{
"family_name": "Stewart",
"given_name": "E. M.",
"orcid": "0000-0002-5092-3140",
"clpid": "Stewart-Emily-M"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0003-3252-7109",
"clpid": "Bucholz-C-E"
}
],
"abstract": "Contact metamorphism of carbonate rocks is a complex process, often characterized by chemical and isotopic disequilibrium and dominated by open-system fluid flow. As such, a handful of recent studies have applied the relatively new tool of carbonate clumped isotope thermometry across km-scale contact aureoles to track conditions from low to high grade. Results have been particularly intriguing among low grade carbonates at the extreme outer edge of the metamorphic aureole. We therefore present results of carbonate clumped isotope analysis combined with detailed petrography and sample characterization to explore the onset of metamorphism in the Alta stock contact aureole, Utah. In addition to focusing on a few densely sampled field profiles near the lowest-grade talc isograd, we perform mm-scale microsampling to assess the relationship between heterogeneous reaction features and carbonate clumped isotopes. We find that elevated metamorphic temperatures (~ 275–300 °C) are recorded by matrix dolomite only in samples which underwent corresponding recrystallization and grain size reduction, and that the boundary between recrystallized and un-recrystallized samples is consistently expressed in the field across a ~ 33 m wide zone. At the microscale, clumped isotopes reveal very local equilibration and recrystallization, recording differing prograde and retrograde reaction temperatures within a few millimeters. Carbonate clumped isotope thermometry and traditional stable isotopes are further used to explore heterogeneous fluid compositions and channelized flow in the outer aureole.
",
"doi": "10.1007/s00410-023-02061-5",
"issn": "0010-7999",
"publisher": "Springer Science and Business Media LLC",
"publication": "Contributions to Mineralogy and Petrology",
"publication_date": "2023-11",
"series_number": "11",
"volume": "178",
"issue": "11",
"pages": "81"
},
{
"id": "authors:xgvt1-v1d45",
"collection": "authors",
"collection_id": "xgvt1-v1d45",
"cite_using_url": "https://authors.library.caltech.edu/records/xgvt1-v1d45",
"type": "article",
"title": "Petrology and Geochemistry of Adak Island Plutonic Xenoliths: Implications for Primitive Magma Generation and Crustal Differentiation in the Aleutian Island Arc",
"author": [
{
"family_name": "Sosa",
"given_name": "Emma S",
"orcid": "0000-0002-1765-6191",
"clpid": "Sosa-Emma-S"
},
{
"family_name": "Bucholz",
"given_name": "Claire E",
"orcid": "0000-0003-3252-7109",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Barickman",
"given_name": "Mattison H"
},
{
"family_name": "VanTongeren",
"given_name": "Jill A",
"orcid": "0000-0002-9702-3107"
},
{
"family_name": "Setera",
"given_name": "Jacob B",
"orcid": "0000-0002-2038-6727"
},
{
"family_name": "Kay",
"given_name": "Suzanne Mahlburg",
"orcid": "0000-0003-1125-3209"
},
{
"family_name": "Kay",
"given_name": "Robert W"
}
],
"abstract": "Deep crustal cumulates in arcs offer a window into the chemistry and crystallization conditions (P–T–H2O–fO2) of primitive basalts in the upper mantle and lower crust and can be studied in ancient exhumed terranes or in xenoliths erupted in young arc lavas. Here, we expand on previous studies and thoroughly characterize the extensive xenolith suites erupted from the Mt. Moffett and Mt. Adagdak volcanic centers (Adak Island, Central Aleutians), which range from primitive ultramafic cumulates to more evolved amphibole gabbros and hornblendites. We present detailed petrography as well as in situ trace and major element mineral chemistry. We use these data to calculate pressure, temperature, and fO2 estimates for the xenoliths, and compare these findings to experimental results to understand the crystallization sequence and P–T–H2O–fO2 under which the cumulates formed. The Moffett crystallization sequence is defined by early amphibole fractionation and an abrupt shift in oxide compositions from chromite to magnetite, while the Adagdak suite is characterized by simultaneous saturation of amphibole+plagioclase and oxide compositions that become increasingly aluminous before magnetite saturation. Olivine–spinel oxybarometry of the Adagdak xenoliths indicates that they are oxidized relative to mid-ocean ridge basalt (MORB:FMQ +0.1 to +2.1). Highly fractionated REE and elevated Sr/Y ratios are observed in clinopyroxene from the most primitive cumulates, consistent with a contribution from a basaltic eclogite melt. This basaltic eclogite melt is hypothesized to come from partial melting of the slab or through melting of basalt introduced into the subarc mantle through forearc subduction erosion. These signatures are greatly diminished in the more evolved lithologies, which can be explained through fractionation of plagioclase and amphibole. Our findings support the presence of a complex magmatic plumbing system beneath Adak, with Mt. Moffett and Mt. Adagdak volcanic centers tapping compositionally distinct sources. More broadly, our results are consistent with studies suggesting that low-degree basaltic eclogite melts through slab melting or forearc subduction erosion contribute to arc magmas in the Aleutians, although the associated geochemical signatures are easily obscured by differentiation in the crust.
",
"doi": "10.1093/petrology/egad073",
"issn": "0022-3530",
"publisher": "Oxford University Press (OUP)",
"publication": "Journal of Petrology",
"publication_date": "2023-10-01",
"series_number": "10",
"volume": "64",
"issue": "10",
"pages": "egad073"
},
{
"id": "authors:zn43c-91y53",
"collection": "authors",
"collection_id": "zn43c-91y53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221205-230336036",
"type": "article",
"title": "Fe\u00b3\u207a/Fe\u1d40 ratios of amphiboles determined by high spatial resolution single-crystal synchrotron M\u00f6ssbauer spectroscopy",
"author": [
{
"family_name": "Ratschbacher",
"given_name": "Barbara C.",
"orcid": "0000-0002-2112-7225",
"clpid": "Ratschbacher-Barbara-C"
},
{
"family_name": "Jackson",
"given_name": "Jennifer M.",
"orcid": "0000-0002-8256-6336",
"clpid": "Jackson-J-M"
},
{
"family_name": "Toellner",
"given_name": "Thomas S.",
"clpid": "Toellner-Thomas-S"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Sturhahn",
"given_name": "Wolfgang",
"orcid": "0000-0002-9606-4740",
"clpid": "Sturhahn-Wolfgang"
},
{
"family_name": "Solomatova",
"given_name": "Natalia V.",
"orcid": "0000-0002-2331-3427",
"clpid": "Solomatova-Natalia-V"
}
],
"abstract": "The Fe\u00b3\u207a/Fe\u1d40 ratios (Fe\u00b3\u207a/[Fe\u00b2\u207a+Fe\u00b3\u207a]) in minerals can be used to understand their crystallization and post-crystallization conditions. However, as natural minerals are often zoned and contain inclusions, bulk techniques, e.g., wet chemistry, may not provide accurate Fe\u00b3\u207a/Fe\u1d40 values for a single phase of interest. We determined Fe\u00b3\u207a/Fe\u1d40 ratios of amphiboles in different crystallographic orientations by single-crystal synchrotron M\u00f6ssbauer spectroscopy (SMS) in energy and time domain modes from four volcanic localities (Long Valley Caldera, Mount St. Helens, Lassen Volcanic Center, U.S.A., and Mt. Pinatubo, Philippines). The high spatial resolution (as low as 12 \u00d7 12 \u03bcm spot size) and standard-free nature of SMS allow the detection of intra-grain compositional heterogeneities in Fe\u00b3\u207a/Fe\u1d40 with relatively low uncertainties.\n\nWe combine SMS with major element compositions, water contents, and hydrogen isotope compositions to document the Fe\u00b3\u207a/Fe\u1d40 ratios as a function of mineral composition and post-crystallization dehydrogenation. Spectra were fitted with up to five distinct sites: ferrous iron on M(1), M(2), M(3), and ferric iron on M(2) and M(3), consistent with X-ray diffraction studies on single crystals of amphibole. The Fe\u00b3\u207a/Fe\u1d40 ratios range from 0.14 \u00b1 0.03 (Long Valley Caldera), 0.51 to 0.63 \u00b1 0.02 (representing intra-grain heterogeneities, Mount St. Helens) to 0.86 \u00b1 0.03 (Lassen Volcanic Center). The latter grain experienced post-crystallization dehydrogenation, shown by its low water content (0.6 \u00b1 0.05 wt%) and its elevated hydrogen isotope composition (\u03b4D = +25 \u00b1 3\u2030 relative to SMOW). The Fe\u00b3\u207a/Fe\u1d40 ratios of 0.62 \u00b1 0.01 and 0.20 \u00b1 0.01 of two Mt. Pinatubo grains correlate with high-Al\u2082O\u2083 cores and low-Al\u2082O\u2083 rims and smaller phenocrysts in the sample, respectively. This study shows that SMS is capable of distinguishing two different domains with dissimilar Fe\u00b3\u207a/Fe\u1d40 values formed under different crystallization conditions, demonstrating that SMS in combination with major element, water, and hydrogen isotope compositions allows the interpretation of amphibole Fe\u00b3\u207a/Fe\u1d40 ratios in the context of crystallization and post-crystallization processes.",
"doi": "10.2138/am-2022-8115",
"issn": "0003-004X",
"publisher": "Mineralogical Society of America",
"publication": "American Mineralogist",
"publication_date": "2023-01",
"series_number": "1",
"volume": "108",
"issue": "1",
"pages": "70-86"
},
{
"id": "authors:kmvdz-y1920",
"collection": "authors",
"collection_id": "kmvdz-y1920",
"cite_using_url": "https://authors.library.caltech.edu/records/kmvdz-y1920",
"type": "article",
"title": "Secular variability in zircon phosphorus concentrations prevents simple petrogenetic classification",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Liebmann",
"given_name": "J.",
"orcid": "0000-0002-0739-3148"
},
{
"family_name": "Spencer",
"given_name": "C. J."
}
],
"abstract": "Phosphorus (P) concentrations in zircon have been used to discriminate their derivation from metaluminous versus strongly peraluminous granites (SPGs) based on the empirical observation of lower P concentrations in zircon from Phanerozoic metaluminous versus peraluminous granites. Higher P concentrations in zircon from Phanerozoic SPGs reflect enhanced apatite solubility in peraluminous melts and overall higher P concentrations in peraluminous granites. However, SPGs derived from partial melting of Precambrian sedimentary rocks have lower P concentrations compared to Phanerozoic metaluminous granites, reflecting lower P concentrations in Precambrian versus Phanerozoic sedimentary sources. We demonstrate that zircons from Precambrian SPGs also have lower P concentrations compared to Phanerozoic counterparts, likely reflecting lower P concentrations in their parental melts. Applying the P-in-zircon proxy to the detrital zircon record does not effectively discriminate between metaluminous and peraluminous sources and underestimates contributions from peraluminous granites. Although detrital zircons are an important early Earth archive, a uniformitarian perspective cannot always be applied when using trace element proxies developed on Phanerozoic samples.
",
"doi": "10.7185/geochemlet.2240",
"issn": "2410-339X",
"publisher": "European Association of Geochemistry",
"publication": "Geochemical Perspectives Letters",
"publication_date": "2022-11",
"volume": "24",
"pages": "12-16"
},
{
"id": "authors:xnwky-r4n64",
"collection": "authors",
"collection_id": "xnwky-r4n64",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221031-575177800.3",
"type": "article",
"title": "Coevolution of sedimentary and strongly peraluminous granite phosphorus records",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
}
],
"abstract": "Phosphorus plays an important role in both surface biological cycles as a critical macronutrient and in magmatic systems as the backbone for trace element-rich phosphate minerals. Phosphorus cycling between igneous and sedimentary systems throughout Earth history has had potentially profound effects on biogeochemical cycles. Previous studies have focused on the impacts of enhanced contribution of phosphorus from igneous rocks on marine phosphorus budgets. In contrast, the effect of changing sedimentary phosphorus abundances on the phosphorus budget of magmas has not been investigated. Here I present a compilation of phosphorus concentrations in strongly peraluminous granites (SPGs), which are derived through the partial melting of sedimentary rocks, spanning the past \u223c3.5 billion years. Maximum phosphorus concentrations of SPGs increase abruptly in the Phanerozoic, closely following a similar, previously documented increase in phosphorus concentrations in marine siliciclastic sediments deposited after 720 Ma. The effect of metamorphic, magmatic, and subsolidus processes on SPG bulk-rock phosphorus concentrations are considered in turn. Lower average bulk-rock phosphorus concentrations in SPGs derived from metasedimentary rocks deposited prior to 720 Ma likely reflect lower phosphorus concentrations of their metasedimentary sources. The SPG compilation both confirms previous observations of phosphorus abundances in the marine sedimentary record and provides an alternative archive in that it integrates large volumes of continental shelf to slope sedimentary rocks. A clear shift in the crustal phosphorus cycle is documented with the initiation of enhanced recycling of sedimentary phosphorus into the igneous crust, where it can be again weathered and returned to the ocean to fuel further photosynthesis. Although phosphorus concentrations in zircon have been used to distinguish between derivation from strongly peraluminous \"S-type\" from metaluminous \"I-type\" granites, the results presented here suggest that phosphorus concentrations in SPGs have a time dependency and that phosphorus concentrations in zircon from SPGs may vary similarly in time.",
"doi": "10.1016/j.epsl.2022.117795",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2022-10-15",
"volume": "596",
"pages": "Art. No. 117795"
},
{
"id": "authors:r2rxa-sm025",
"collection": "authors",
"collection_id": "r2rxa-sm025",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220705-346489000",
"type": "article",
"title": "Whole-rock geochemistry and zircon O-Hf isotope compositions of ca. 2.35\u00a0Ga strongly peraluminous granites: Implications for increase in zircon \u03b4\u00b9\u2078O values during the Paleoproterozoic",
"author": [
{
"family_name": "Xie",
"given_name": "Shi-Wen",
"clpid": "Xie-Shi-Wen"
},
{
"family_name": "Wang",
"given_name": "Fang",
"clpid": "Wang-Fang"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Liu",
"given_name": "Fu-Lai",
"clpid": "Liu-Fu-Lai"
},
{
"family_name": "Wang",
"given_name": "Pei-Zhi",
"clpid": "Wang-Pei-Zhi"
},
{
"family_name": "Bao",
"given_name": "Ze-Min",
"clpid": "Bao-Ze-Min"
},
{
"family_name": "Liu",
"given_name": "Dun-Yi",
"clpid": "Liu-Dun-Yi"
}
],
"abstract": "Zircon oxygen isotope ratios have been used to trace the incorporation of sedimentary rocks into magmas. The dramatic increase in maximum zircon \u03b4\u00b9\u2078O values in the Paleoproterozoic observed in global databases coincides with changes in surface environments (e.g., the rise of subaerial and oxidative weathering), implying a connection between elevated zircon \u03b4\u00b9\u2078O and these changes. Zircon \u03b4\u00b9\u2078O between 2.5 and 2.2 Ga, however, is relatively under-constrained owing to limited available data in this age range. To augment data from this critical time period and understand potential causes for the elevated zircon \u03b4\u00b9\u2078O values, we report U-Pb zircon ages and \u03b4\u00b9\u2078O values of zircon, as well as, whole-rock major and trace element geochemistry of Paleoproterozoic strongly peraluminous granites (SPGs) from the southwestern margin of the Yangtze Block (China). Our geochronological data demonstrate that these SPGs crystallized at \u223c2.35 Ga and that inherited zircon with ages of 2428\u20132721 Ma are present in these granites, indicating the source rocks of these granites were deposited, subsequently metamorphosed, and partially melted between 2.43 and 2.35 Ga. Synmagmatic zircon from samples dated in this study have \u03b5Hf(t) values of \u22126.4 to \u22120.9 and high \u03b4\u00b9\u2078O values of 7.6\u20139.9\u2030, elevated above the maximum value observed in Archean zircon (\u223c7\u2030). These granites can be divided into two groups based on whole-rock geochemistry. Both Group 1 and Group 2 granites were derived from a similar high \u03b4\u00b9\u2078O, metapelitic source, but were generated by dehydration melting and hydrous melting, respectively. Our results demonstrate that the fine-grained sedimentary rocks from which the SPGs were derived had relatively high \u03b4\u00b9\u2078O (as compared to older sedimentary rocks) by 2.43\u20132.35 Ga. The depositional time interval of the high-\u03b4\u00b9\u2078O sedimentary sources for SPGs studied here coincides with the emergence of continental crust above sea level and the Great Oxidation Event. Supporting the findings of previous studies, the contemporaneity of our dataset with these changes in Earth's surface environments suggests that subaerial and potentially oxidative weathering contributed (at least partially) to the elevation of \u03b4\u00b9\u2078O of fine-grained sedimentary rocks. Recycling of these high-\u03b4\u00b9\u2078O sedimentary rocks into magmas contributed to the dramatic change in \u03b4\u00b9\u2078O of magmatic zircon in the earliest Paleoproterozoic. In addition, although this study is focused on a single locality, our results suggest that the abrupt shift observed in global zircon \u03b4\u00b9\u2078O data sets likely occurred by 2.35 Ga. Last, a literature compilation of zircon \u03b4\u00b9\u2078O data from SPGs suggested that zircon \u03b4\u00b9\u2078O values may have also experienced a stepwise increase in the Neoproterozoic to Phanerozoic from 12 to 14\u2030. The coincidence of these increases in zircon \u03b4\u00b9\u2078O values with global oxygenation events suggests that atmospheric oxygenation may have contributed to the increase in \u03b4\u00b9\u2078O of sedimentary rocks.",
"doi": "10.1016/j.gca.2022.06.029",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2022-09-01",
"volume": "332",
"pages": "186-202"
},
{
"id": "authors:14psx-r6k51",
"collection": "authors",
"collection_id": "14psx-r6k51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220606-735977000",
"type": "article",
"title": "Constraints on Early Paleozoic Deep-Ocean Oxygen Concentrations From the Iron Geochemistry of the Bay of Islands Ophiolite",
"author": [
{
"family_name": "Stolper",
"given_name": "Daniel A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-Daniel-A"
},
{
"family_name": "Pu",
"given_name": "Xiaofei",
"orcid": "0000-0003-2120-7054",
"clpid": "Pu-Xiaofei"
},
{
"family_name": "Lloyd",
"given_name": "Max K.",
"orcid": "0000-0001-9367-2698",
"clpid": "Lloyd-Max-K"
},
{
"family_name": "Christensen",
"given_name": "Nikolas I.",
"orcid": "0000-0003-2956-040X",
"clpid": "Christensen-Nikolas-I"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Lange",
"given_name": "Rebecca A.",
"orcid": "0000-0003-0309-6178",
"clpid": "Lange-Rebecca-A"
}
],
"abstract": "The deep ocean is generally considered to have changed from anoxic in the Precambrian to oxygenated by the Late Paleozoic (\u223c420\u2013400 Ma) due to changes in atmospheric oxygen concentrations. When the transition occurred, that is, in the Early Paleozoic or not until the Late Paleozoic, is less well constrained. To address this, we measured Fe\u00b3\u207a/\u03a3Fe of volcanic rocks, sheeted dykes, gabbros, and ultramafic rocks from the Early Paleozoic (\u223c485 Ma) Bay of Islands (BOI) ophiolite as a proxy for hydrothermal alteration in the presence or absence of O\u2082 derived from deep marine fluids. Combining this data with previously published data from the BOI indicates that volcanic rocks are oxidized relative to intrusive crustal rocks (0.35 \u00b1 0.02 vs. 0.19 \u00b1 0.01, 1 standard error), which we interpret to indicate that the volcanic section was altered by marine-derived fluids that contained some dissolved O\u2082. We compare our results directly to the Macquarie Island and Troodos ophiolites, drilled oceanic crust, previously compiled data for ophiolitic volcanic rocks, and newly compiled data for ophiolitic intrusive rocks. These comparisons show that the BOI volcanic (but not intrusive) rocks are oxidized relative to Precambrian equivalents, but are less oxidized relative to Late Paleozoic to modern equivalents. We interpret these results to indicate that the Early Paleozoic ocean contained dissolved O\u2082, but at concentrations \u223c2.4\u00d7 lower than for the Late Paleozoic to today.",
"doi": "10.1029/2021gc010196",
"issn": "1525-2027",
"publisher": "American Geophysical Union",
"publication": "Geochemistry, Geophysics, Geosystems",
"publication_date": "2022-07",
"series_number": "7",
"volume": "23",
"issue": "7",
"pages": "Art. No. e2021GC010196"
},
{
"id": "authors:29aqa-1vz07",
"collection": "authors",
"collection_id": "29aqa-1vz07",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211110-161345996",
"type": "article",
"title": "Evidence for polybaric fractional crystallization in a continental arc: Hidden Lakes mafic complex, Sierra Nevada batholith, California",
"author": [
{
"family_name": "Lewis",
"given_name": "Madeline J.",
"orcid": "0000-0001-7968-2822",
"clpid": "Lewis-Madeline-J"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Jagoutz",
"given_name": "Oliver E.",
"clpid": "Jagoutz-Oliver-E"
}
],
"abstract": "Although the voluminous granitoids that constitute the upper crust of the Sierra Nevada batholith (California) have been investigated in detail, comparatively few studies focus on the origin of mafic bodies at similar crustal levels. Here, we present field and petrographic observations, geochronology, and geochemistry of the Hidden Lakes mafic complex in the central-eastern Sierra Nevada batholith. Our results show that the complex comprises norites, gabbros, monzondiorites, and monzonites that record fractional crystallization of a hydrous (~\u20093 wt% H\u2082O), non-primitive basalt within the upper crust (0.3 GPa) at c. 95\u201396 Ma. To quantitatively model the generation of the observed lithologies, we construct a two-stage polybaric crystallization model based on cumulate and melt-like bulk-rock compositions. In the first step, we model fractionation of a primitive, mantle-derived basalt at\u2009>\u200930 km depth, generating dominantly pyroxenite cumulates. The evolution of the derivative melt (67% of melt mass remaining) is then modeled to fractionate at 12 km depth to produce the observed lithologies within the Hidden Lakes mafic complex. Extension of this model to higher-silica melt compositions (>\u200965 wt% SiO\u2082) replicates observed granodiorite compositions in the batholith, suggesting that polybaric crystallization could be an important process for the generation of arc granitoid melts. The depth of differentiation in continental arcs is debated, as field observations indicate abundant lower crustal fractionation while experimental data suggest that high-pressure crystallization of hydrous basalts cannot produce the non-peraluminous granitoid compositions observed in continental arc batholiths. Our model supports polybaric differentiation as one potential mechanism to resolve this inconsistency.",
"doi": "10.1007/s00410-021-01844-y",
"issn": "0010-7999",
"publisher": "Springer",
"publication": "Contributions to Mineralogy and Petrology",
"publication_date": "2021-11",
"series_number": "11",
"volume": "176",
"issue": "11",
"pages": "Art. No. 90"
},
{
"id": "authors:b1jtb-g8c13",
"collection": "authors",
"collection_id": "b1jtb-g8c13",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210503-125957872",
"type": "article",
"title": "Emergence of continents above sea\u2010level influences sediment melt composition",
"author": [
{
"family_name": "Liebmann",
"given_name": "Janne",
"clpid": "Liebmann-Janne"
},
{
"family_name": "Spencer",
"given_name": "Christopher J.",
"clpid": "Spencer-Christopher-J"
},
{
"family_name": "Kirkland",
"given_name": "Christopher L.",
"orcid": "0000-0003-3367-8961",
"clpid": "Kirkland-Christopher-L"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "He",
"given_name": "Xiao-Fang",
"clpid": "He-Xiao-Fang"
},
{
"family_name": "Santosh",
"given_name": "M.",
"clpid": "Santosh-M"
},
{
"family_name": "Xia",
"given_name": "Xiaoping P.",
"clpid": "Xia-Xiaoping-P"
},
{
"family_name": "Martin",
"given_name": "Laure",
"clpid": "Martin-Laure"
},
{
"family_name": "Evans",
"given_name": "Noreen J.",
"clpid": "Evans-Noreen-J"
}
],
"abstract": "The Archean\u2010Proterozoic transition heralded a number of fundamental changes on Earth, including the oxygenation of the atmosphere, a marked emergence of continents above sea\u2010level, and an increase in \u03b4\u00b9\u2078O of felsic magmas. The potential drivers for the latter are changes in the composition of supracrustal material or increased crustal reworking. Although the onset of subduction\u2010induced continental collision and associated enhanced crustal recycling could produce high\u2010\u03b4\u00b9\u2078O felsic magmas, temporally constrained zircon \u03b4\u00b9\u2078O reveals an increase in \u03b4\u00b9\u2078O at ~2.35 Ga that predates the oldest widely recognized supercontinent. In this work, we use the O and Hf isotope ratios of magmatic zircon crystals in Archean and Proterozoic sediment\u2010derived granitoids of the North China Craton to track the incorporation of supracrustal material into magmas. The results are consistent with a Paleoproterozoic increase of continental freeboard producing sedimentary reservoirs with comparatively elevated \u03b4\u00b9\u2078O that subsequently partially melted to generate the granitoids.",
"doi": "10.1111/ter.12531",
"issn": "0954-4879",
"publisher": "Wiley",
"publication": "Terra Nova",
"publication_date": "2021-10",
"series_number": "5",
"volume": "33",
"issue": "5",
"pages": "465-474"
},
{
"id": "authors:xa44s-2vw16",
"collection": "authors",
"collection_id": "xa44s-2vw16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210823-154141103",
"type": "article",
"title": "Coupling sulfur and oxygen isotope ratios in sediment melts across the Archean-Proterozoic transition",
"author": [
{
"family_name": "Liebmann",
"given_name": "Janne",
"orcid": "0000-0002-0739-3148",
"clpid": "Liebmann-Janne"
},
{
"family_name": "Spencer",
"given_name": "Christopher J.",
"orcid": "0000-0003-4264-3701",
"clpid": "Spencer-Christopher-J"
},
{
"family_name": "Kirkland",
"given_name": "Christopher L.",
"orcid": "0000-0003-3367-8961",
"clpid": "Kirkland-Christopher-L"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Xia",
"given_name": "Xiao-Ping",
"orcid": "0000-0002-3203-039X",
"clpid": "Xia-Xiao-Ping"
},
{
"family_name": "Martin",
"given_name": "Laure",
"clpid": "Martin-Laure"
},
{
"family_name": "Kitchen",
"given_name": "Nami",
"clpid": "Kitchen-Nami"
},
{
"family_name": "Shumlyanskyy",
"given_name": "Leonid",
"orcid": "0000-0002-6775-4419",
"clpid": "Shumlyanskyy-Leonid"
}
],
"abstract": "The Archean-Proterozoic transition marks a time of fundamental geologic, biologic, and atmospheric changes to the Earth system, including oxygenation of the atmosphere (termed the Great Oxygenation Event; GOE), and the emergence of continents above sea level. The impacts of the GOE on Earth's surface environment are imprinted on the geologic record, including the disappearance of mass-independent fractionation of sulfur isotopes (S-MIF). Temporally overlapping geologic and geochemical observations (e.g. a change in oxygen isotope ratio of sediments and an increase in subaerial volcanism) imply the widespread subaerial emergence of continents was coeval with atmospheric oxygenation. Here we present triple sulfur isotope ratios in pyrite and oxygen isotope ratios in garnet and zircon in a global suite of Archean and Proterozoic granitoids derived from the partial melting of sedimentary protoliths. These crustal melts record an increase in average garnet and zircon \u03b4\u00b9\u2078O from 7.2\u2030 before 2.3 Ga to 10.0\u2030 post-2.3 Ga. Pre-2.3 Ga granitoids show small S-MIF signatures with \u0394\u00b3\u00b3S ranging from \u22120.29\u2030 to 0.13\u2030, whereas post-2.3 Ga granitoids record S-MDF (i.e. \u0394\u00b3\u00b3S = 0\u2030). The combination of sulfur and oxygen isotope signatures in the same sample with zircon U-Pb geochronology provides new insights on a potential causal link between the emergence of continents and Paleoproterozoic atmospheric oxygenation.",
"doi": "10.1016/j.gca.2021.05.045",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2021-08-15",
"volume": "307",
"pages": "242-257"
},
{
"id": "authors:sba7c-0q245",
"collection": "authors",
"collection_id": "sba7c-0q245",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200817-094633188",
"type": "article",
"title": "Sulfur isotope behavior during metamorphism and anatexis of Archean sedimentary rocks: A case study from the Ghost Lake batholith, Ontario, Canada",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Biasi",
"given_name": "Joseph A.",
"orcid": "0000-0003-1196-7877",
"clpid": "Biasi-J-A"
},
{
"family_name": "Beaudry",
"given_name": "Patrick",
"clpid": "Beaudry-P"
},
{
"family_name": "Ono",
"given_name": "Shuhei",
"orcid": "0000-0002-1348-9584",
"clpid": "Ono-Shuhei"
}
],
"abstract": "Recycling of surface-derived sulfur into the deep earth can impart distinct sulfur isotope signatures to magmas. The details of sulfur transfer from sedimentary rocks to magmas (and ultimately igneous rocks) through metamorphism and devolatilization and/or partial melting, however, is difficult to trace. To understand this process in detail we studied multiple-sulfur isotope compositions of sulfides in the Archean (c. 2685 Ma) Ghost Lake batholith (GLB) and its surrounding host metasedimentary rocks of the Superior Craton (Ontario, Canada) by high spatial resolution secondary ion mass spectrometry, complemented by high-precision gas source isotope ratio mass spectrometry measurements. The GLB comprises strongly peraluminous biotite+cordierite, biotite+muscovite, and muscovite+garnet+tourmaline granites to leucogranites, which are thought to represent the partial melts of surrounding metagreywackes and metapelites. The metasedimentary rocks display a range of metamorphic grades increasing from biotite-chlorite (280-380 \u00b0C) at \u223c5 km away from the GLB to sillimanite-K-feldspar grade (\u223c660 \u00b0C) immediately adjacent to the batholith, thus providing a natural experiment to understand sulfur isotope variations from low- to high-grade Archean sedimentary rocks, as well as granites representative of their partial melts.\nWe find that metasedimentary sulfide \u03b4\u00b3\u2074S values increase with progressive metamorphism at most 2-3\u2030 (from \u22121\u2030 up to +1 to +2\u2030). An increase in \u03b4\u00b3\u2074S values in pyrrhotite during prograde metamorphism can be explained through Rayleigh fractionation during pyrite desulfidation reactions. Pyrite from all but one of the granite samples preserve \u03b4\u00b3\u2074S values similar to that of the high-grade metasedimentary rocks, indicating that partial melting did not result in significant fractionation of \u03b4\u00b3\u2074S. The exception to this is one granite sample from a part of the batholith characterized by abundant metasedimentary inclusions. This sample contains pyrite with heterogeneous and low \u03b4\u00b3\u2074S values (down to \u221216\u2030) which likely resulted from incomplete homogenization of sulfur between the granitic melt and metasedimentary inclusions. Small (several tenths of a permil), mostly positive \u0394\u00b3\u00b3S are observed in both the metasedimentary rocks and granites.\nOur results suggest that Archean strongly peraluminous granites could be a high-fidelity archive to quantify the bulk sulfur isotope composition of the Archean siliciclastic sediments. Further, our findings indicate that subduction of reduced sulfur-bearing sediments in the Archean with \u03b4\u00b3\u2074S at or near 0\u2030 should result in release of sulfur-bearing fluids in the mantle wedge with similar values (within a few permil). S-MIF (if initially present in Archean surface material) may be preserved during this process. However, the absence of S-MIF in igneous rocks does not preclude assimilation of Archean sedimentary material as either S-MIF may not be originally present in the Archean sedimentary sulfur and/or homogenization or dilution could obscure any S-MIF originally present in assimilated Archean sediments.",
"doi": "10.1016/j.epsl.2020.116494",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2020-11-01",
"volume": "549",
"pages": "Art. No. 116494"
},
{
"id": "authors:npe67-g5w79",
"collection": "authors",
"collection_id": "npe67-g5w79",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190909-093503339",
"type": "article",
"title": "Oxygen fugacity at the base of the Talkeetna arc, Alaska",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Kelemen",
"given_name": "Peter B.",
"orcid": "0000-0003-4757-0855",
"clpid": "Kelemen-P-B"
}
],
"abstract": "The origin of the more oxidized nature of arc magmas as compared to that of mid-ocean ridge basalts (MORB) is debated, considered to be either a feature of their mantle source, or produced during crustal transit and eruption. Fe^(3+)/Fe^T ratios (Fe^(3+)/[Fe^(3+)\u2009+\u2009Fe^(2+)]) in arc volcanic rocks and glasses and thermodynamic oxybarometry on mantle xenoliths from arc lavas indicate elevated magmatic oxygen fugacity (fO_2), whereas, redox-sensitive trace elements ratios and abundances in arc volcanic rocks have been used to suggest that arcs have source regions with fO_2 similar to the MORB source. Here, we take an alternative approach by calculating the fO_2 of the uppermost mantle and lowermost ultramafic cumulates from the accreted Jurassic Talkeetna arc (Alaska). This approach allows us to quantify the fO_2 of the sub-arc mantle and of primary arc magmas crystallizing at the base of an island arc, which have not been affected by processes during crustal transit and eruption which could affect their fO_2. Implementing olivine\u2013spinel oxybarometry, we find that the upper mantle (harzburgites and lherzolites) and ultramafic cumulates (clinopyroxenites and dunites) crystallized between +\u20090.4 and +\u20092.3 log units above the fayalite-magnetite-quartz buffer, consistent with previous studies suggesting that the sub-arc mantle is oxidized relative to that of MORB. In addition, the Talkeetna paleo-arc allows us to examine coeval lavas and their redox-sensitive trace element ratios (e.g., V/Sc). The average V/Sc ratios of high MgO (>\u20096 wt%) lavas are 6.7\u2009\u00b1\u20091.6 (2\u03c3), similar to that of MORB. However, V/Sc ratios must be interpretted in terms the degree of partial melting, as well as, the initial V/Sc ratio of the mantle source in order to derive information about fO_2 of their mantle source. The V/Sc ratios of Talkeetna lavas are consistent with the elevated fO_2 recorded in the sub-arc mantle and primitive cumulates (olivine Mg# [Mg/(Mg\u2009+\u2009Fe)]\u2009\u00d7\u2009100\u2009>\u200982) if a depleted mantle source underwent 15\u201320% melting. Our results suggest that the arc mantle is, on average, more oxidized than the MORB source and that V/Sc ratios must be interpreted in the context of a partial melting model where all model parameters are appropriate for arc magma genesis. This study reconciles V/Sc ratios in arc volcanic rocks with fO_2 of primary arc basalts and the sub-arc mantle from the same locality.",
"doi": "10.1007/s00410-019-1609-z",
"issn": "0010-7999",
"publisher": "Springer",
"publication": "Contributions to Mineralogy and Petrology",
"publication_date": "2019-10",
"series_number": "10",
"volume": "174",
"issue": "10",
"pages": "Art. No. 79"
},
{
"id": "authors:kf2zy-ks753",
"collection": "authors",
"collection_id": "kf2zy-ks753",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191114-112103999",
"type": "article",
"title": "Strongly Peraluminous Granites across the Archean\u2013Proterozoic Transition",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Spencer",
"given_name": "Christopher J.",
"clpid": "Spencer-C-J"
}
],
"abstract": "Strongly peraluminous granites (SPGs) form through the partial melting of metasedimentary rocks and therefore represent archives of the influence of assimilation of sedimentary rocks on the petrology and chemistry of igneous rocks. With the aim of understanding how variations in sedimentary rock characteristics across the Archean\u2013Proterozoic transition might have influenced the igneous rock record, we compiled and compared whole-rock chemistry, mineral chemistry, and isotope data from Archean and Paleo- to Mesoproterozoic SPGs. This time period was chosen as the Archean\u2013Proterozoic transition broadly coincides with the stabilization of continents, the rise of subaerial weathering, and the Great Oxidation Event (GOE), all of which left an imprint on the sedimentary rock record. Our compilation of SPGs is founded on a detailed literature review of the regional geology, geochronology, and inferred origins of the SPGs, which suggest derivation from metasedimentary source material. Although Archean and Proterozoic SPGs are similar in terms of mineralogy or major-element composition owing to their compositions as near-minimum melts in the peraluminous haplogranite system, we discuss several features of their mineral and whole-rock chemistry. First, we review a previous analysis of Archean and Proterozoic SPGs biotite and whole-rock compositions indicating that Archean SPGs, on average, are more reduced than Proterozoic SPGs. This observation suggests that Proterozoic SPGs were derived from metasedimentary sources that on average had more oxidized bulk redox states relative to their Archean counterparts, which could reflect an increase in atmospheric O\u2082 levels and more oxidized sedimentary source rocks after the GOE. Second, based on an analysis of Al\u2082O\u2083/TiO\u2082 whole-rock ratios and zircon saturation temperatures, we conclude that Archean and Proterozoic SPGs formed through partial melting of metasedimentary rocks over a similar range of melting temperatures, with both 'high-' and 'low-'temperature SPGs being observed across all ages. This observation suggests that the thermo-tectonic processes resulting in the heating and melting of metasedimentary rocks (e.g. crustal thickening or underplating of mafic magmas) occurred during generation of both the Archean and Proterozoic SPGs. Third, bulk-rock CaO/Na\u2082O, Rb/Sr, and Rb/Ba ratios indicate that Archean and Proterozoic SPGs were derived from partial melting of both clay-rich (i.e. pelites) and clay-poor (i.e. greywackes) source regions that are locality specific, but not defined by age. This observation, although based on a relatively limited dataset, indicates that the source regions of Archean and Proterozoic SPGs were similar in terms of sediment maturity (i.e. clay component). Last, existing oxygen isotope data for quartz, zircon, and whole-rocks from Proterozoic SPGs show higher values than those of Archean SPGs, suggesting that bulk sedimentary \u00b9\u2078O/\u00b9\u2076O ratios increased across the Archean\u2013Proterozoic boundary. The existing geochemical datasets for Archean and Proterozoic SPGs, however, are limited in size and further work on these rocks is required. Future work must include detailed field studies, petrology, geochronology, and constraints on sedimentary source ages to fully interpret the chemistry of this uniquely useful suite of granites.",
"doi": "10.1093/petrology/egz033",
"issn": "0022-3530",
"publisher": "Oxford University Press",
"publication": "Journal of Petrology",
"publication_date": "2019-07",
"series_number": "7",
"volume": "60",
"issue": "7",
"pages": "1299-1348"
},
{
"id": "authors:1g0ay-b6151",
"collection": "authors",
"collection_id": "1g0ay-b6151",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190412-084938417",
"type": "article",
"title": "Neoproterozoic to early Phanerozoic rise in island arc redox state due to deep ocean oxygenation and increased marine sulfate levels",
"author": [
{
"family_name": "Stolper",
"given_name": "Daniel A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
}
],
"abstract": "A rise in atmospheric O_2 levels between 800 and 400 Ma is thought to have oxygenated the deep oceans, ushered in modern biogeochemical cycles, and led to the diversification of animals. Over the same time interval, marine sulfate concentrations are also thought to have increased to near-modern levels. We present compiled data that indicate Phanerozoic island arc igneous rocks are more oxidized (Fe^(3+)/\u03a3Fe ratios are elevated by 0.12) vs. Precambrian equivalents. We propose this elevation is due to increases in deep-ocean O_2 and marine sulfate concentrations between 800 and 400 Ma, which oxidized oceanic crust on the seafloor. Once subducted, this material oxidized the subarc mantle, increasing the redox state of island arc parental melts, and thus igneous island arc rocks. We test this using independently compiled V/Sc ratios, which are also an igneous oxybarometer. Average V/Sc ratios of Phanerozoic island arc rocks are elevated (by +1.1) compared with Precambrian equivalents, consistent with our proposal for an increase in the redox state of the subarc mantle between 800 and 400 Ma based on Fe^(3+)/\u03a3Fe ratios. This work provides evidence that the more oxidized nature of island arc vs. midocean-ridge basalts is related to the subduction of material oxidized at the Earth's surface to the subarc mantle. It also indicates that the rise of atmospheric O_2 and marine sulfate to near-modern levels by the late Paleozoic influenced not only surface biogeochemical cycles and animal diversification but also influenced the redox state of island arc rocks, which are building blocks of continental crust.",
"doi": "10.1073/pnas.1821847116",
"pmcid": "PMC6500123",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2019-04-30",
"series_number": "18",
"volume": "116",
"issue": "18",
"pages": "8746-8755"
},
{
"id": "authors:0wmp2-drr48",
"collection": "authors",
"collection_id": "0wmp2-drr48",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190506-075110988",
"type": "article",
"title": "A Comparison of Oxygen Fugacities of Strongly Peraluminous Granites across the Archean\u2013Proterozoic Boundary",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Stolper",
"given_name": "Edward M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
},
{
"family_name": "Breaks",
"given_name": "Frederick W.",
"clpid": "Breaks-F-W"
}
],
"abstract": "We constrain the oxygen fugacity (\u2060f_(O2)\u2060) of strongly peraluminous granites [SPGs; i.e. granites (sensu lato) generated through the partial melting of sediments] across the Archean\u2013Proterozoic boundary, which coincides roughly with the Great Oxygenation Event (GOE), to understand whether secular changes in atmospheric O_2 levels may be imprinted on the f_(O2) of igneous rocks. SPGs were chosen to maximize the potential effects of sediments in their sources on the f_(O2) of the magmas. We studied 28 Archean (2685\u20132547\u2009Ma) and 31 Meso- to Paleoproterozoic (1885\u20131420\u2009Ma) geographically distributed samples from North America, spanning two cratons (Superior and Wyoming) and both orogenic and anorogenic Proterozoic provinces (Trans-Hudson Orogen, Wopmay Orogen, and SW USA). We present an analysis of both new and previously published whole-rock major and trace element data and mineral major element chemistry from the samples. All the studied samples are peraluminous high-silica plutonic rocks (all contain >67\u2009wt % SiO_2, and 92% are true granites with >69\u2009wt % SiO_2), and biotite + muscovite\u2009\u00b1\u2009garnet\u2009\u00b1\u2009tourmaline\u2009\u00b1\u2009sillimanite are the primary aluminous minerals in all samples. Whole-rock major element and trace element abundances of all samples are consistent with derivation by partial melting of aluminous sediments. To constrain the f_(O2) of crystallization of the SPGs, we developed an alphaMELTS-based method that takes advantage of the sensitivity of biotite Fe^T/(Fe^T + Mg) ratios to f_(O2)\u2060. This method is able to reproduce experimental and empirical data where biotite compositions and whole-rock compositions, pressures and temperatures of crystallization and f_(O2) are known. For the SPGs in this study, alphaMELTS modeling indicates that 68% of Proterozoic samples crystallized at an f_(O2) between NNO \u20131 and NNO +1\u00b71 (where NNO is nickel\u2013nickel oxide buffer), whereas the remaining Proterozoic samples (32%) and most of the Archean samples (75%) crystallized at \u2264NNO \u20132. The simplest explanation of these results is that the Proterozoic SPGs were derived from metasedimentary source rocks that on average had more oxidized bulk redox states relative to their Archean counterparts. The bulk redox state of the metasedimentary source rocks of SPGs of all ages is defined by the relative abundances of oxidized (e.g. Fe^(3+) and S^(6+)) and reduced (e.g. organic matter) material. The crystallization of both Archean and Proterozoic samples at f_(O2) values of \u2264NNO \u20132 is consistent with them having their f_(O2) buffered by graphite (formed from organic carbon) in their source regions. However, the dominantly low f_(O2) (\u2264NNO \u20132) values of the Archean SPGs plausibly reflects the presence of organic material and relatively reduced metasedimentary rocks in their source region prior to the GOE. In contrast, the elevated f_(O2) values of the majority of the Proterozoic SPGs may reflect enhanced sulfate contents or increased Fe^(3+)/Fe^T in sediments after the GOE, which, in terms of the bulk redox state of their metasedimentary source region, would have offset the reducing nature of organic matter present there.",
"doi": "10.1093/petrology/egy091",
"issn": "0022-3530",
"publisher": "Oxford University Press",
"publication": "Journal of Petrology",
"publication_date": "2018-11",
"series_number": "11",
"volume": "59",
"issue": "11",
"pages": "2123-2156"
},
{
"id": "authors:dcx07-p3113",
"collection": "authors",
"collection_id": "dcx07-p3113",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170406-085435368",
"type": "article",
"title": "Oxygen Isotope Trajectories of Crystallizing Melts: Insights from Modeling and the Plutonic Record",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Jagoutz",
"given_name": "Oliver",
"clpid": "Jagoutz-O"
},
{
"family_name": "VanTongeren",
"given_name": "Jill A.",
"clpid": "VanTongeren-J-A"
},
{
"family_name": "Setera",
"given_name": "Jacob",
"clpid": "Setera-J"
},
{
"family_name": "Wang",
"given_name": "Zhengrong",
"orcid": "0000-0003-3149-0236",
"clpid": "Wang-Zhengrong"
}
],
"abstract": "Elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth. The \u03b4^(18)O value of a melt, however, can also increase through closed-system fractional crystallization. In order to quantify the change in melt \u03b4^(18)O due to crystallization, we develop a detailed closed-system fractional crystallization mass balance model and apply it to six experimentally- and naturally-determined liquid lines of descent (LLDs), which cover nearly complete crystallization intervals (melt fractions of 1 to <0.1). The studied LLDs vary from anhydrous tholeiitic basalts to hydrous high-K and calc-alkaline basalts and are characterized by distinct melt temperature-SiO_2 trajectories, as well as, crystallizing phase relationships. Our model results demonstrate that melt fraction-temperature-SiO_2 relationships of crystallizing melts, which are strongly a function of magmatic water content, will control the specific \u03b4^(18)O path of a crystallizing melt. Hydrous melts, typical of subduction zones, undergo larger increases in \u03b4^(18)O during early stages of crystallization due to their lower magmatic temperatures, greater initial increases in SiO_2 content, and high temperature stability of low \u03b4^(18)O phases, such as oxides, amphibole, and anorthitic plagioclase (versus albite). Conversely, relatively dry, tholeiitic melts only experience significant increases in \u03b4^(18)O at degrees of crystallization greater than 80%. Total calculated increases in melt \u03b4^(18)O of 1.0 to 1.5\u2030 can be attributed to crystallization from \u223c50 to 70 wt.% SiO_2 for modeled closed-system crystallizing melt compositions. As an example application, we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences, a relatively dry, tholeiitic sequence from the Upper and Upper Main Zones (UUMZ) of the Bushveld Complex (South Africa) and a high-K, hydrous sequence from the arc-related Dariv Igneous Complex (Mongolia). These two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed-system fractional crystallization and their LLDs have been modeled in detail. We calculated equilibrium melt \u03b4^(18)O values using the measured mineral \u03b4^(18)O values and calculated mineral-melt fractionation factors. Increases of 2-3\u2030 and 1-1.5\u2030 in the equilibrium melts are observed for the Dariv Igneous Complex and the UUMZ of the Bushveld Complex, respectively. Closed-system fractional crystallization model results reproduce the 1\u2030 increase observed in the equilibrium melt \u03b4^(18)O for the Bushveld UUMZ, whereas for the Dariv Igneous Complex assimilation of high \u03b4^(18)O material is necessary to account for the increase in melt \u03b4^(18)O values. Assimilation of evolved supracrustal material is also confirmed with Sr and Nd isotope analyses of clinopyroxene from the sequence. Beginning with a range of mantle-derived basalt \u03b4^(18)O values of 5.7\u2030 (\"pristine\" mantle) to \u223c7.0\u2030 (heavily subduction-influenced mantle), our model results demonstrated that high-silica melts (i.e. granites) with \u03b4^(18)O of up to 8.5\u2030 can be produced through fractional crystallization alone. Lastly, we model the zircon-melt \u03b4^(18)O fractionations of different LLDs, emphasizing their dependence on the specific SiO_2-T relationships of a given crystallizing melt. Wet, relatively cool granitic melts will have larger zircon-melt fractionations, potentially by \u223c1.5\u2030, compared to hot, dry granites. Therefore, it is critical to constrain zircon-melt fractionations specific to a system of interest when using zircon \u03b4^(18)O values to calculate melt \u03b4^(18)O.",
"doi": "10.1016/j.gca.2017.03.027",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2017-06-15",
"volume": "207",
"pages": "154-184"
},
{
"id": "authors:dsnjs-a5693",
"collection": "authors",
"collection_id": "dsnjs-a5693",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161117-091918674",
"type": "article",
"title": "Constraining the time scales of magmatic differentiation with U-Pb zircon geochronology",
"author": [
{
"family_name": "Bucholz",
"given_name": "C. E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Eddy",
"given_name": "M. P.",
"clpid": "Eddy-M-P"
},
{
"family_name": "Jagoutz",
"given_name": "O.",
"clpid": "Jagoutz-O"
},
{
"family_name": "Bowring",
"given_name": "S. A.",
"clpid": "Bowring-S-A"
},
{
"family_name": "Schmidt",
"given_name": "M. W.",
"clpid": "Schmidt-M-W"
},
{
"family_name": "Sambuu",
"given_name": "O.",
"clpid": "Sambuu-O"
}
],
"abstract": "Quantifying the time scales of magmatic differentiation is critical for understanding the rate at which silicic plutonic and volcanic rocks form. Directly dating this process is difficult because locations with both clear evidence for fractional crystallization and the accessory phases necessary for radiometric dating are rare. Early zircon saturation, however, appears to be characteristic of many high-K, arc-related melts due to their generally elevated initial Zr concentrations. Thus, high-K plutonic series are ideal candidates to study the time scales of magmatic differentiation using zircon U-Pb geochronology. This study focuses on the Dariv Igneous Complex in western Mongolia where early saturation of zircon in a suite of cogenetic, upper crustal (<0.5 GPa) igneous rocks ranging from ultramafic cumulates to evolved granitoids allows us to date magmatic differentiation. Crystallization ages from six samples across the sequence indicate that magmatic fractionation from a basalt to high-silica (>65 wt% SiO_2) melt occurred in \u2264590 \u00b1 350 k.y. This estimate is greater than modeled time scales of conductive cooling of a single intrusion and physical segregation of minerals from a melt, suggesting that continued influx of heat through magmatic activity in the complex may have prolonged cooling and thus time scales associated with the production of silica-enriched melts.",
"doi": "10.1130/G38505.1",
"issn": "0091-7613",
"publisher": "Geological Society of America",
"publication": "Geology",
"publication_date": "2017-01",
"series_number": "1",
"volume": "45",
"issue": "1",
"pages": "11-14"
},
{
"id": "authors:kk3zx-0h760",
"collection": "authors",
"collection_id": "kk3zx-0h760",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180112-092037923",
"type": "article",
"title": "Fractional crystallization of high-K arc magmas: biotite- versus amphibole-dominated fractionation series in the Dariv Igneous Complex, Western Mongolia",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Jagoutz",
"given_name": "Oliver",
"clpid": "Jagoutz-O"
},
{
"family_name": "Schmidt",
"given_name": "Max W.",
"clpid": "Schmidt-M-W"
},
{
"family_name": "Sambuu",
"given_name": "Oyungerel",
"clpid": "Sambuu-O"
}
],
"abstract": "Many studies have documented hydrous fractionation of calc-alkaline basalts producing tonalitic, granodioritic, and granitic melts, but the origin of more alkaline arc sequences dominated by high-K monzonitic suites has not been thoroughly investigated. This study presents results from a combined field, petrologic, and whole-rock geochemical study of a paleo-arc alkaline fractionation sequence from the Dariv Range of the Mongolian Altaids. The Dariv Igneous Complex of Western Mongolia is composed of a complete, moderately hydrous, alkaline fractionation sequence ranging from phlogopite-bearing ultramafic and mafic cumulates to quartz\u2013monzonites to late-stage felsic (63\u201375 wt% SiO_2) dikes. A volumetrically subordinate more hydrous, amphibole-dominated fractionation sequence is also present and comprises amphibole (\u00b1phlogopite) clinopyroxenites, gabbros, and diorites. We present 168 whole-rock analyses for the biotite- and amphibole-dominated series. First, we constrain the liquid line of descent (LLD) of a primitive, alkaline arc melt characterized by biotite as the dominant hydrous phase through a fractionation model that incorporates the stepwise subtraction of cumulates of a fixed composition. The modeled LLD reproduces the geochemical trends observed in the \"liquid-like\" intrusives of the biotite series (quartz\u2013monzonites and felsic dikes) and follows the water-undersaturated albite\u2013orthoclase cotectic (at 0.2\u20130.5 GPa). Second, as distinct biotite- and amphibole-dominated fractionation series are observed, we investigate the controls on high-temperature biotite versus amphibole crystallization from hydrous arc melts. Analysis of a compilation of hydrous experimental starting materials and high-Mg basalts saturated in biotite and/or amphibole suggests that the degree of K enrichment controls whether biotite will crystallize as an early high-T phase, whereas the degree of water saturation is the dominant control of amphibole crystallization. Therefore, if a melt has the appropriate major-element composition for early biotite and amphibole crystallization, as is true of the high-Mg basalts from the Dariv Igneous Complex, the relative proximity of these two phases to the liquidus depends on the H_2O concentration in the melt. Third, we compare the modeled high-K LLD and whole-rock geochemistry of the Dariv Igneous Complex to the more common calc-alkaline trend. Biotite and K-feldspar fractionation in the alkaline arc series results in the moderation of K_2O/Na_2O values and LILE concentrations with increasing SiO_2 as compared to the more common calc-alkaline series characterized by amphibole and plagioclase crystallization and strong increases in K_2O/Na_2O values. Lastly, we suggest that common calc-alkaline parental melts involve addition of a moderate pressure, sodic, fluid-dominated slab component while more alkaline primitive melts characterized by early biotite saturation involve the addition of a high-pressure potassic sediment melt.",
"doi": "10.1007/s00410-014-1072-9",
"issn": "0010-7999",
"publisher": "Springer",
"publication": "Contributions to Mineralogy and Petrology",
"publication_date": "2014-11",
"series_number": "5",
"volume": "168",
"issue": "5",
"pages": "Art. No. 1072"
},
{
"id": "authors:jcq7a-cgq96",
"collection": "authors",
"collection_id": "jcq7a-cgq96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180111-162502718",
"type": "article",
"title": "Fractional crystallization of high-K arc magmas: biotite- versus amphibole-dominated fractionation series in the Dariv Igneous Complex, Western Mongolia",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Jagoutz",
"given_name": "Oliver",
"clpid": "Jagoutz-O"
},
{
"family_name": "Schmidt",
"given_name": "Max W.",
"clpid": "Schmidt-M-W"
},
{
"family_name": "Sambuu",
"given_name": "Oyungerel",
"clpid": "Sambuu-O"
}
],
"abstract": "Many studies have documented hydrous fractionation of calc-alkaline basalts producing tonalitic, granodioritic, and granitic melts, but the origin of more alkaline arc sequences dominated by high-K monzonitic suites has not been thoroughly investigated. This study presents results from a combined field, petrologic, and whole-rock geochemical study of a paleo-arc alkaline fractionation sequence from the Dariv Range of the Mongolian Altaids. The Dariv Igneous Complex of Western Mongolia is composed of a complete, moderately hydrous, alkaline fractionation sequence ranging from phlogopite-bearing ultramafic and mafic cumulates to quartz\u2013monzonites to late-stage felsic (63\u201375 wt% SiO2) dikes. A volumetrically subordinate more hydrous, amphibole-dominated fractionation sequence is also present and comprises amphibole (\u00b1phlogopite) clinopyroxenites, gabbros, and diorites. We present 168 whole-rock analyses for the biotite- and amphibole-dominated series. First, we constrain the liquid line of descent (LLD) of a primitive, alkaline arc melt characterized by biotite as the dominant hydrous phase through a fractionation model that incorporates the stepwise subtraction of cumulates of a fixed composition. The modeled LLD reproduces the geochemical trends observed in the \"liquid-like\" intrusives of the biotite series (quartz\u2013monzonites and felsic dikes) and follows the water-undersaturated albite\u2013orthoclase cotectic (at 0.2\u20130.5 GPa). Second, as distinct biotite- and amphibole-dominated fractionation series are observed, we investigate the controls on high-temperature biotite versus amphibole crystallization from hydrous arc melts. Analysis of a compilation of hydrous experimental starting materials and high-Mg basalts saturated in biotite and/or amphibole suggests that the degree of K enrichment controls whether biotite will crystallize as an early high-T phase, whereas the degree of water saturation is the dominant control of amphibole crystallization. Therefore, if a melt has the appropriate major-element composition for early biotite and amphibole crystallization, as is true of the high-Mg basalts from the Dariv Igneous Complex, the relative proximity of these two phases to the liquidus depends on the H2O concentration in the melt. Third, we compare the modeled high-K LLD and whole-rock geochemistry of the Dariv Igneous Complex to the more common calc-alkaline trend. Biotite and K-feldspar fractionation in the alkaline arc series results in the moderation of K2O/Na2O values and LILE concentrations with increasing SiO2 as compared to the more common calc-alkaline series characterized by amphibole and plagioclase crystallization and strong increases in K2O/Na2O values. Lastly, we suggest that common calc-alkaline parental melts involve addition of a moderate pressure, sodic, fluid-dominated slab component while more alkaline primitive melts characterized by early biotite saturation involve the addition of a high-pressure potassic sediment melt.",
"doi": "10.1007/s00410-014-1072-9",
"issn": "0010-7999",
"publisher": "Springer",
"publication": "Contributions to Mineralogy and Petrology",
"publication_date": "2014-11",
"series_number": "5",
"volume": "168",
"issue": "5",
"pages": "Art. no. 1072"
},
{
"id": "authors:gk22b-f2t10",
"collection": "authors",
"collection_id": "gk22b-f2t10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180111-162502460",
"type": "article",
"title": "Phlogopite- and clinopyroxene-dominated fractional crystallization of an alkaline primitive melt: petrology and mineral chemistry of the Dariv Igneous Complex, Western Mongolia",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Jagoutz",
"given_name": "Oliver",
"clpid": "Jagoutz-O"
},
{
"family_name": "Schmidt",
"given_name": "Max W.",
"clpid": "Schmidt-M-W"
},
{
"family_name": "Sambuu",
"given_name": "Oyungerel",
"clpid": "Sambuu-O"
}
],
"abstract": "We present field relationships, petrography, and mineral major and trace element data for the Neoproterozoic Dariv Igneous Complex of the Altaids of Western Mongolia. This unique complex of high-K plutonic rocks is composed of well-exposed, km-scale igneous intrusions of wehrlites, phlogopite wehrlites, apatite-bearing phlogopite clinopyroxenites, monzogabbros, monzodiorites, and clinopyroxene-bearing monzonites, all of which are intruded by late stage lamprophyric and aplitic dikes. The biotite-dominated igneous complex intrudes depleted harzburgitic serpentinite. The observed lithological variability and petrographic observations suggest that the plutonic rocks can be ascribed to a fractionation sequence defined by olivine + clinopyroxene \u00b1 Fe\u2013Ti oxides \u2192 phlogopite + apatite \u2192 K-feldspar + plagioclase \u2192 amphibole + quartz. Notably, phlogopite is the dominant hydrous mafic mineral. Petrogenesis of the observed lithologies through a common fractionation sequence is supported by a gradual decrease in the Mg# [molar Mg/(Fe_(total) + Mg) \u00d7 100] of mafic minerals. Crystallization conditions are derived from experimental phase petrology and mineral chemistry. The most primitive ultramafic cumulates crystallized at \u22640.5 GPa and 1,210\u20131,100 \u00b0C and oxygen fugacity (fO_2) of +2\u20133 \u2206FMQ (log units above the fayalite\u2013quartz\u2013magnetite buffer). Trace element modeling using clinopyroxene and apatite rare earth element compositions indicates that the dominant mechanism of differentiation was fractional crystallization. The trace element composition of a parental melt was calculated from primitive clinopyroxene compositions and compares favorably with the compositions of syn-magmatic lamprophyres that crosscut the fractionation sequence. The parental melt composition is highly enriched in Th, U, large ion lithophile elements, and light rare earth elements and has a pronounced negative Nb\u2013Ta depletion, suggestive of an alkaline primitive melt originating from a subduction-imprinted mantle. Comparison with a global compilation of primitive arc melts demonstrates that Dariv primitive melts are similar in composition to high-K primitive melts found in some continental arcs. Thus, the high-K fractionation sequence exposed in the Dariv Igneous Complex may be a previously unrecognized important fractionation sequence resulting in alkali-rich upper crustal granitoids in continental arc settings.",
"doi": "10.1007/s00410-014-0994-6",
"issn": "0010-7999",
"publisher": "Springer",
"publication": "Contributions to Mineralogy and Petrology",
"publication_date": "2014-04",
"series_number": "4",
"volume": "167",
"issue": "4",
"pages": "Art. No. 994"
},
{
"id": "authors:tna8v-bcp64",
"collection": "authors",
"collection_id": "tna8v-bcp64",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180111-162502212",
"type": "article",
"title": "Post-entrapment modification of volatiles and oxygen fugacity in olivine-hosted melt inclusions",
"author": [
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Gaetani",
"given_name": "Glenn A.",
"clpid": "Gaetani-G-A"
},
{
"family_name": "Behn",
"given_name": "Mark D.",
"clpid": "Behn-M-D"
},
{
"family_name": "Shimizu",
"given_name": "Nobumichi",
"clpid": "Shimizu-Nobumichi"
}
],
"abstract": "The solubilities of volatiles (H_2O, CO_2, S, F, and Cl) in basaltic melts are dependent on variables such as temperature, pressure, melt composition, and redox state. Accordingly, volatile concentrations can change dramatically during the various stages of a magma's existence: from generation, to ascent through the mantle and crust, to final eruption at the Earth's surface. Olivine-hosted melt inclusions have the potential to preserve volatile concentrations at the time of entrapment due to the protection afforded by the host olivine against decompression and changes to the oxidation state of the external magma. Recent studies, however, have demonstrated that rapid diffusive re-equilibration of H_2O and oxygen fugacity (f_(O_2)) can occur within olivine-hosted melt inclusions. Here we present volatile, hydrogen isotope, and major element data from dehydration experiments and a quantitative model that assesses proposed mechanisms for diffusive re-equilibration of H_2O and f_(O_2) in olivine-hosted melt inclusions. Our comprehensive set of data for the behavior of common magmatic volatiles (H_2O, CO_2, F, Cl, and S) demonstrates that post-entrapment modification of CO_2, and to a lesser extent S, can also occur. We show that the CO_2 and S concentrations within an included melt decrease with progressive diffusive H_2O loss, and propose that this occurs due to dehydration-induced changes to the internal pressure of the inclusion. Therefore, deriving accurate estimates for pre-eruptive CO_2 and S concentrations from olivine-hosted melt inclusions requires accounting for the amount of CO_2 and S hosted in vapor bubbles. We find, however, that Cl and F concentrations in olivine-hosted melt inclusions are not affected by diffusive re-equilibration through the host olivine nor by dehydration-induced pressure changes within the melt inclusion. Our results indicate that measured H_2O, CO_2 and S concentrations and Fe^(3+)/\u03a3Fe ratios of included melts are not necessarily representative of the melt at the time of entrapment and thus are not reliable proxies for upper mantle conditions.",
"doi": "10.1016/j.epsl.2013.05.033",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2013-07-15",
"volume": "374",
"pages": "145-155"
},
{
"id": "authors:s2f4s-2tq77",
"collection": "authors",
"collection_id": "s2f4s-2tq77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180111-162501944",
"type": "article",
"title": "Rapid reequilibration of H_2O and oxygen fugacity in olivine-hosted melt inclusions",
"author": [
{
"family_name": "Gaetani",
"given_name": "Glenn A.",
"clpid": "Gaetani-G-A"
},
{
"family_name": "O'Leary",
"given_name": "Julie A.",
"clpid": "O'Leary-J-A"
},
{
"family_name": "Shimizu",
"given_name": "Nobumichi",
"clpid": "Shimizu-Nobumichi"
},
{
"family_name": "Bucholz",
"given_name": "Claire E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Newville",
"given_name": "Matthew",
"clpid": "Newville-M"
}
],
"abstract": "The solubility of H_2O in silicate melt drops substantially with decreasing pressure, so that a magma initially containing several weight percent H_2O in a crustal magma reservoir is left with only a few thousand parts per million following ascent and eruption at the Earth's surface. This rapid release of volatiles makes determining the pre-eruptive H_2O contents of magmas very difficult. Olivine-hosted melt inclusions are thought to retain their H_2O because they are protected from decompression by the strength of the host crystal, and pre-eruptive concentrations obtained from melt inclusions have been used to both estimate the amount of H_2O in the upper mantle and investigate its role in the melt generation process. The greatest uncertainty involved in constraining upper mantle conditions from melt inclusions is the potential for rapid diffusive loss or gain of H^+ (protons) through the host olivine. Here we present results from hydration and dehydration experiments that demonstrate that, contrary to the widely held view, H_2O loss or gain in melt inclusions is not limited by redox reactions and significant fluxes of H^+ through the host olivine are possible on very short time scales. We also show that the Fe^(3+)/\u03a3Fe of an olivine-hosted melt inclusion maintains equilibrium with the external environment via diffusion of point defects through the host olivine. Our results demonstrate that, while pre-eruptive H_2O and Fe^(3+)/\u03a3Fe can be reliably estimated, olivine-hosted melt inclusions do not necessarily retain a record of the H_2O and O_2 fugacity conditions at which they formed. High-H_2O melt inclusions are particularly susceptible to diffusive dehydration, and therefore are not reliable proxies for the state of the upper mantle.",
"doi": "10.1130/G32992.1",
"issn": "0091-7613",
"publisher": "Geological Society of America",
"publication": "Geology",
"publication_date": "2012-10",
"series_number": "10",
"volume": "40",
"issue": "10",
"pages": "915-918"
},
{
"id": "authors:mg25s-ydp92",
"collection": "authors",
"collection_id": "mg25s-ydp92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120228-161222506",
"type": "article",
"title": "Oxygen isotope constraints on the origin of high-Cr garnets from kimberlites",
"author": [
{
"family_name": "Wang",
"given_name": "Zhengrong",
"orcid": "0000-0003-3149-0236",
"clpid": "Wang-Zhengrong"
},
{
"family_name": "Bucholz",
"given_name": "Claire",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Skinner",
"given_name": "Brian",
"clpid": "Skinner-B"
},
{
"family_name": "Shimizu",
"given_name": "Nobumichi",
"clpid": "Shimizu-Nobumichi"
},
{
"family_name": "Eiler",
"given_name": "John",
"clpid": "Eiler-J-M"
}
],
"abstract": "The association between diamonds and high-Cr, sub-calcic garnets from kimberlites suggests that garnets have experienced high pressure (and presumably, high temperature) conditions in the subcontinental lithosphere\nmantle (SCLM). The oxygen isotope compositions of these garnets are generally reported to be lower than average values of mantle olivines (~5.2\u2030)\u2014opposite the sense of oxygen isotope fractionation expected at high-temperature equilibrium, and to correlate negatively with their Cr-contents. These observations were interpreted to indicate the sub-calcic garnets either are derived from melting Cr-enriched but ^(18)O-depleted source in the SCLM, or have experienced cryptic metasomatism by high-Cr, high-Mg#, but ^(18)O-depleted fluids/melts in the SCLM or during their ascent to the surface. We investigate the possibility that oxygen isotope characteristics of these garnets instead reflect an analytical artifact that reduces the measured \u03b4^(18)O of garnets in proportion to its Cr content\u2014a so-called 'Cr-effect'. Mixtures of garnet standards (UWG-2) plus various amounts of pure Cr-metal were measured for \u03b4^(18)O-values by infrared-laser fluorination technique (ILFT). Our results show that oxygen isotope compositions of sample mixtures vary systematically as a function of Cr-content and O_(2)-yield. Mass-balance analyses indicate that the correlation between the measured \u03b4^(18)O-value and Cr-content is an analytical artifact mostly due to isotopic fractionation between the extracted-O_(2) and chromium oxyfluorides left as residues in the sample chamber during the ILFT analyses, which amounts to a decrease in the measured \u03b4^(18)O values of ~0.064\u2030 for the increase of every wt.% Cr_(2)O_(3) present in garnets. After applying our experimentally-calibrated correction factor to garnet samples in garnet peridotite xenoliths from South Africa, our study reveals an equilibrium oxygen isotope fractionation between the Cr-poor garnet and coexisting olivine (i.e., garnet\u2265olivine) with a fractionation factor of ~0.28\u2030. More importantly, high-Cr garnets (Cr_(2)O_(3)>5%), after correction for the 'Cr-effect', are actually enriched, rather than depleted, in 18O compared with low-Cr garnets, suggesting the involvement of ^(18)O-enriched crustal materials during their formation. We hypothesize a fluid-flow model using depthdependent Cr partitioning. This model simultaneously explains relatively high-\u03b4^(18)O-values and Cr and Mg enrichment in garnets, implying that the reduced C\\H\\O fluids that are responsible for the formation of diamonds in both eclogite and peridotite xenoliths in kimberlites, are also responsible for transporting Cr to oxidized locations where the Cr partition coefficient between garnet and fluids is high.",
"doi": "10.1016/j.epsl.2011.09.061",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2011-12-15",
"series_number": "3-4",
"volume": "312",
"issue": "3-4",
"pages": "337-347"
},
{
"id": "authors:ey6k3-sej49",
"collection": "authors",
"collection_id": "ey6k3-sej49",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180111-162501653",
"type": "article",
"title": "Fluid flow and Al transport during quartz-kyanite vein formation, Unst, Shetland Islands, Scotland",
"author": [
{
"family_name": "Bucholz",
"given_name": "C. E.",
"orcid": "0000-0001-5332-8278",
"clpid": "Bucholz-C-E"
},
{
"family_name": "Ague",
"given_name": "J. J.",
"clpid": "Ague-J-J"
}
],
"abstract": "Quartz-kyanite veins, adjacent alteration selvages and surrounding 'precursor' wall rocks in the Dalradian Saxa Vord Pelite of Unst in the Shetland Islands (Scotland) were investigated to constrain the geochemical alteration and mobility of Al associated with channelized metamorphic fluid infiltration during the Caledonian Orogeny. Thirty-eight samples of veins, selvages and precursors were collected, examined using the petrographic microscope and electron microprobe, and geochemically analysed. With increasing grade, typical precursor mineral assemblages include, but are not limited to, chlorite+chloritoid, chlorite+chloritoid+kyanite, chlorite+chloritoid+staurolite and garnet+staurolite+kyanite+chloritoid. These assemblages coexist with quartz, white mica (muscovite, paragonite, margarite), and Fe-Ti oxides. The mineral assemblage of the selvages does not change noticeably with metamorphic grade, and consists of chloritoid, kyanite, chlorite, quartz, white mica and Fe-Ti oxides. Pseudosections for selvage and precursor bulk compositions indicate that the observed mineral assemblages were stable at regional metamorphic conditions of 550\u2013600 \u00b0C and 0.8\u20131.1 GPa. A mass balance analysis was performed to assess the nature and magnitude of geochemical alteration that produced the selvages adjacent to the veins. On average, selvages lost about \u221226% mass relative to precursors. Mass losses of Na, K, Ca, Rb, Sr, Cs, Ba and volatiles were \u221230 to \u221260% and resulted from the destruction of white mica. Si was depleted from most selvages and transported locally to adjacent veins; average selvage Si losses were about \u221250%. Y and rare earth elements were added due to the growth of monazite in cracks cutting apatite. The mass balance analysis also suggests some addition of Ti occurred, consistent with the presence of rutile and hematite-ilmenite solid solutions in veins. No major losses of Al from selvages were observed, but Al was added in some cases. Consequently, the Al needed to precipitate vein kyanite was not derived locally from the selvages. Veins more than an order of magnitude thicker than those typically observed in the field would be necessary to accommodate the Na and K lost from the selvages during alteration. Therefore, regional transport of Na and K out of the local rock system is inferred. In addition, to account for the observed abundances of kyanite in the veins, large fluid-rock ratios (102\u2013103 m3fluid m\u22123rock) and time-integrated fluid fluxes in excess of \u223c104 m3fluid m\u22122rock are required owing to the small concentrations of Al in aqueous fluids. It is concluded that the quartz-kyanite veins and their selvages were produced by regional-scale advective mass transfer by means of focused fluid flow along a thrust fault zone. The results of this study provide field evidence for considerable Al mass transport at greenschist to amphibolite facies metamorphic conditions, possibly as a result of elevated concentrations of Al in metamorphic fluids due to alkali-Al silicate complexing at high pressures.",
"doi": "10.1111/j.1525-1314.2009.00851.x",
"issn": "0263-4929",
"publisher": "Wiley-Blackwell",
"publication": "Journal of Metamorphic Geology",
"publication_date": "2010-01",
"series_number": "1",
"volume": "28",
"issue": "1",
"pages": "19-39"
}
]