@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107381, title ="Heating events in the nascent solar system recorded by rare earth element isotopic fractionation in refractory inclusions", author = "Hu, J. Y. and Dauphas, N.", journal = "Science Advances", volume = "7", number = "2", pages = "Art. No. eabc2962", month = "January", year = "2021", doi = "10.1126/sciadv.abc2962", issn = "2375-2548", url = "https://resolver.caltech.edu/CaltechAUTHORS:20210108-111355586", note = "© 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). \n\nSubmitted 16 April 2020; Accepted 16 November 2020; Published 6 January 2021. \n\nCAI samples were provided by P. R. Heck and the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum (FG-FT-3, 4, 6, 7, 8, 9, and 10) and S. Simon (TS32) (see full catalog numbers in Table 1). Discussions with F. M. Richter, P. R. Heck, N. X. Nie, C. Chen, H. Zeng, S. M. Aarons, and A. W. Heard were greatly appreciated. We are grateful to H. Palme and an anonymous reviewer for thorough and constructive reviews, which greatly improved the quality of the manuscript. \n\nThis work was supported by NASA grants NNX17AE86G, NNX17AE87G, 80NSSC17K0744, and 80NSSC20K0821; NSF grant EAR-2001098 to N.D.; and NASA grant 80NSSC17K0251 to A.M.D. \n\nAuthor contributions: J.Y.H., N.D., and F.L.H.T. conceived the study; F.L.H.T. and L.G. selected the samples in a previous study; F.L.H.T. characterized, extracted, and digested the samples; J.Y.H. established the measurement protocol, carried out the isotopic analyses of REEs, did the modeling, and wrote a first draft of the manuscript under the guidance of N.D.; Z.Z. and J.Y.H. carried out the isotopic analyses of Ti; A.M.D. helped with thermodynamic modeling; F.J.C. provided some input on the possible astrophysical setting for CAI formation; N.D., F.L.H.T., R.Y., T.J.I., and J.Y.H. developed the FPLC system; B.L.A.C. helped with comparison of the data with previous Sr isotopic results; N.D., M.R., E.E.A., M.Y.H., and J.Z. helped with interpretation of previously published Eu NRIXS data. All authors contributed to data interpretation and writing of the manuscript. \n\nCompeting interests: N.D., F.L.H.T., R.Y., T.J.I., and J.Y.H. are inventors on a patent related to this work filed by Orlab Chromatography LLC (no. US9884266B2, filed on 8 July 2014, published on 8 January 2015). The authors declare no other competing interests. \n\nData and materials availability: The OL-REE series of isotope standards used in this study are stored at the Origins Laboratory, The University of Chicago and are available upon request from J.Y.H. or N.D. All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.", revision_no = "12", abstract = "Equilibrium condensation of solar gas is often invoked to explain the abundance of refractory elements in planets and meteorites. This is partly motivated, by the observation that the depletions in both the least and most refractory rare earth elements (REEs) in meteoritic group II calcium-aluminum–rich inclusions (CAIs) can be reproduced by thermodynamic models of solar nebula condensation. We measured the isotopic compositions of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb in eight CAIs to test this scenario. Contrary to expectation for equilibrium condensation, we find light isotope enrichment for the most refractory REEs and more subdued isotopic variations for the least refractory REEs. This suggests that group II CAIs formed by a two-stage process involving fast evaporation of preexisting materials, followed by near-equilibrium recondensation. The calculated time scales are consistent with heating in events akin to FU Orionis– or EX Lupi–type outbursts of eruptive pre–main-sequence stars.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105748, title ="Drivers of zirconium isotope fractionation in Zr-bearing phases and melts: the roles of vibrational, nuclear field shift and diffusive effects", author = "Méheut, Merlin and Ibañez-Mejia, Mauricio", journal = "Geochimica et Cosmochimica Acta", volume = "292", pages = "217-234", month = "January", year = "2021", doi = "10.1016/j.gca.2020.09.028", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201002-090438118", note = "© 2020 Elsevier Ltd. \n\nReceived 5 June 2020, Accepted 22 September 2020, Available online 1 October 2020. \n\nThis research was supported by NSF-EAR grants 1823748 (to MIM) and 1824002 (to FT) and start-up funds to MIM provided by University of Rochester and to FT provided by Caltech. This work was performed using HPC resources from CALMIP (Calcul en Midi-Pyrénées; Grant 2019-P1037). We are grateful for critical evaluations from Editor Mark Rehkämper, Jörn-Frederik Wotzlaw, and two anonymous reviewers, which helped to improve the clarity of this manuscript. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "23", abstract = "Conflicting results exist regarding the mechanisms, direction, and magnitude of Zr isotope fractionation in igneous systems. To better understand the origin of the fractionations observed in magmatic Zr-bearing minerals and bulk rocks, we theoretically investigated the main potential driving processes: thermodynamic equilibrium effects driven by either (i) vibrational energy or (ii) nuclear volume, and (iii) diffusion-driven kinetic effects. Vibrational equilibrium fractionation properties were estimated for zircon (^(VIII)ZrSiO₄), baddeleyite (^(VII)ZrO₂), gittinsite (^(VI)ZrCaSi₂O₇), sabinaite (Na₄^(VIII)Zr₂TiC₄O₁₆), and vlasovite (Na₂^(VI)ZrSi₄O₁₁). These properties show dependency on Zr coordination, as well as the presence of strong covalent bonds (C O, Si O by order of decreasing effect) in the material. More importantly, despite the large variety of structures investigated, the predicted mass-dependent equilibrium fractionations (Δ⁹⁴/⁹⁰Zr ∼±0.05‰ relative to zircon at 800\u202f°C) are systematically one order of magnitude smaller than required to explain the natural variability observed to date in natural settings (δ⁹⁴/⁹⁰Zr from ∼+1 to −5‰). Likewise, careful evaluation of expected nuclear field shift (NFS) effects predict a magnitude of fractionation of ∼0.08‰ (at 800\u202f°C), further supporting the conclusion that equilibrium effects cannot be invoked to explain extreme δ⁹⁴/⁹⁰Zr zircon values. Furthermore, the mass-dependency of all Zr isotope ratios reported in zircon crystals precludes a contribution of NFS effects larger than ∼0.01‰ on δ⁹⁴/⁹⁰Zr. On the other hand, we show that diffusion, and in particular the development of Zr diffusive boundary layers in silicate magmas during fractional crystallization, provides a viable and most likely mechanism to produce permil-level, mass-dependent isotope fractionations similar to those observed in natural systems. We propose testable scenarii to explain the large and contrasting Zr isotopes signatures in different magmatic zircons, which underline the importance of magmatic composition, Zr diffusivity, and crystallization timescales.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107104, title ="Distribution Coefficients of the REEs, Sr, Y, Ba, Th, and U between α-HIBA and AG50W-X8 Resin", author = "Li, Haoyu and Tissot, François L. H.", journal = "ACS Earth and Space Chemistry", month = "December", year = "2020", doi = "10.1021/acsearthspacechem.0c00273", issn = "2472-3452", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201215-141038772", note = "© 2020 American Chemical Society. \n\nReceived 1 October 2020; Accepted 2 December 2020; Revised 2 December 2020; Published online 15 December 2020. \n\nWe thank the three anonymous reviewers and editor Joel D. Blum for constructive criticisms, which greatly helped us to improve the manuscript. This work was supported by grants NASA grants NNX17AE86G, NNX17AE87G, 80NSSC17K0744, and 80NSSC20K0821 and NSF grant EAR-2001098 to N.D.; grant GP2020-003 (provided by Korea Institute of Geoscience and Mineral Resources) to S.-G.L.; NASA grant 80NSSC20K1398 (PI: F.L.H.T., FI: H.L.), NSF grant EAR-1824002, and start-up funds (provided by Caltech) to F.L.H.T. \n\nAuthor Contributions. N.D., F.L.H.T., and S-G.L. conceived the study. S.-G.L. and F.L.H.T. performed the partitioning experiments. H.L. and F.L.H.T. processed and interpreted the data. E.H. conducted Elution 2. H.L. wrote the first draft under F.L.H.T.’s guidance. All authors contributed to writing and/or editing of the manuscript. \n\nThe authors declare no competing financial interest.", revision_no = "15", abstract = "Rare-earth elements (REEs) are known for their similar behaviors, which make their purification through chromatographic techniques particularly challenging. The use of α-hydroxyisobutyric acid (α-HIBA) in combination with a cation-exchange resin is perhaps the most widely used chromatographic technique to separate individual REEs from each other. However, only limited REE partition data between α-HIBA and cation resins exist, which makes it challenging to develop and optimize purification techniques using this platform. Here, we report distribution coefficients (K_d) of REEs, as well as Sr, Y, Ba, Th, and U, between α-HIBA at pH = 4.50 and AG50W-X8 cation-exchange resin, obtained by batch equilibration experiments. For all 19 elements, the distribution coefficients decrease with increasing acid concentration. For the REEs, a linear relationship is observed in log–log space between K_d values and α-HIBA molarity. While the K_d values have been calibrated at pH = 4.50, formulas are provided allowing recasting of the K_d values at any pH. To test the accuracy of the data, we compare elution curves simulated using the newly determined distribution coefficients to actual elution curves. The close agreement between simulated and experimental elution curves demonstrates that the distribution coefficients obtained in this study are effective to devise multielement extraction and purification scheme for high-precision elemental and isotopic analyses of REEs for various applications.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103310, title ="Zirconium stable isotope analysis of zircon by MC-ICP-MS: Methods and application to evaluating intra-crystalline zonation in a zircon megacryst", author = "Tompkins, Hannah G. D. and Zieman, Lisa J.", journal = "Journal of Analytical Atomic Spectrometry", volume = "35", number = "6", pages = "1167-1186", month = "June", year = "2020", doi = "10.1039/c9ja00315k", issn = "0267-9477", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200519-100855433", note = "© 2020 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. \n\nSubmitted 17 Sep 2019; Accepted 05 May 2020; First published 07 May 2020. \n\nDavid McGee is thanked for access to the MIT Nu Plasma II, and Joel DesOrmeau for the careful and time-consuming SEM-CL imaging of MTUR1 at U. Nevada in Reno. Matthew Bown, Chaofeng Li and an anonymous reviewer are thanked for constructive comments that helped improve the final version of this manuscript. This research was supported by a Stephen Pollock Undergraduate Research Grant awarded by the NE section of the Geological Society of America (to HT), NSF-EAR grants 1823748 (to MIM) and 1824002 (to FT) and start-up funds to MIM provided by University of Rochester and to FT provided by Caltech. \n\nThere are no conflicts to declare.", revision_no = "15", abstract = "Zirconium (Zr) plays a key role in the development of phases like zircon (ZrSiO₄) and baddeleyite (ZrO₂) in magmatic systems. These minerals are crucial for the study of geologic time and crustal evolution, and their high resistivity to weathering and erosion results in their preservation on timescales of billions of years. Although zircon and baddeleyite may also preserve a robust record of Zr isotope behavior in high-temperature terrestrial environments, little is known about the factors that control Zr isotope partitioning in magmatic systems, the petrogenetic significance of fractionated compositions, or how these variations are recorded in Zr-rich accessory phases. Here, we describe a new analytical protocol for accurately determining the Zr stable isotope composition of zircon by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), using the double-spike method to correct for procedural and instrumental mass bias. We apply this technique to test whether zircon crystallization in carbonatite magmatic systems is a driver of Zr isotope fractionation by interrogating the internal zonation of a zircon megacryst from the Mud Tank carbonatite (MTUR1). We find the MTUR1 megacryst to lack internal zoning within analytical uncertainties with a mean μ⁹⁴/⁹⁰Zr_(NIST) = −55 ± 28 ppm (2 SD, n = 151), which suggests that zircon crystallization is not a driver of Zr isotope fractionation in carbonatite magmas. This observation is in stark contrast with those made in silicate magmatic systems, raising the possibility that the bonding environment of Zr⁴⁺ ions may be fundamentally different in carbonatite vs. silicate melts. Because of its remarkable homogeneity, the MTUR1 megacryst is an ideal natural reference material for Zr isotopic analysis of zircon using both solution and spatially resolved methods. The reproducibility of a pure Zr solution and our chemically purified zircon fractions indicate that the external reproducibility of our method is on the order of ±28 ppm for μ⁹⁴/⁹⁰Zr, or ±7 ppm per amu, at 95% confidence.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100052, title ="Evidence of presolar SiC in the Allende Curious Marie calcium–aluminium-rich inclusion", author = "Pravdivtseva, O. and Tissot, F. L. H.", journal = "Nature Astronomy", volume = "4", number = "6", pages = "617-624", month = "June", year = "2020", doi = "10.1038/s41550-019-1000-z", issn = "2397-3366", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191125-163016120", note = "© 2020 Springer Nature Limited. \n\nReceived 05 March 2019; Accepted 06 December 2019; Published 27 January 2020. \n\nWe are grateful to D. Nakashima and A. Nguyen for the constructive and thorough review and for the help provided during the editorial process. We thank P. Heck, J. Holstein, and the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum for providing the Curious Marie specimen (catalogue number ME3364-3.2). This work was supported by NASA grant 80NSSC19K0508 to O.P.; a Crosby Postdoctoral Fellowships (MIT), NSF-EAR grant 1824002, and start-up funds provided by Caltech to F.L.H.T.; by NASA grants NNX17AE86G (LARS), NNX17AE87G 531 (Emerging Worlds) and 80NSSC17K0744 (Habitable Worlds) to N.D. \n\nData availability: The data that support the plots within this paper and other findings of this study are provided in the Supplementary Information as Supplementary Tables 1‒4, and are also available from the corresponding author upon reasonable request. \n\nAuthor Contributions: O.P designed the study, conducted the noble gas analyses, treated the data and wrote the first draft of the paper. F.L.H.T. selected, prepared and characterized the studied sample. O.P. and S.A. interpreted the data. N.D. critically contributed to the paper presentation. All the authors contributed to the discussion of the results and commented on the manuscript. \n\nThe authors declare no competing interests. \n\nPeer review information: Nature Astronomy thanks Daisuke Nakashima, Ann Nguyen and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.", revision_no = "24", abstract = "Calcium–aluminium-rich inclusions (CAIs) are one of the first solids to have condensed in the solar nebula, while presolar grains formed in various evolved stellar environments. It is generally accepted that CAIs formed close to the Sun at temperatures above 1,500\u2009K, where presolar grains could not survive, and were then transported to other regions of the nebula where the accretion of planetesimals took place. In this context, a commonly held view is that presolar grains are found solely in the fine-grained rims surrounding chondrules and in the low-temperature fine-grained matrix that binds the various meteoritic components together. Here we demonstrate, on the basis of noble gas isotopic signatures, that presolar SiC grains were incorporated into fine-grained CAIs in the Allende carbonaceous chondrite at the time of their formation, and have survived parent-body processing. This finding provides new clues on the conditions in the nascent Solar System at the condensation of the first solids.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100521, title ="Extreme Zr stable isotope fractionation during magmatic fractional crystallization", author = "Ibañez-Mejia, Mauricio and Tissot, François L. H.", journal = "Science Advances", volume = "5", number = "12", pages = "Art. No. eaax8648", month = "December", year = "2019", doi = "10.1126/sciadv.aax8648", issn = "2375-2548", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200106-080043111", note = "© 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). \n\nSubmitted 30 April 2019; Accepted 4 November 2019; Published 18 December 2019. \n\nWe thank D. McGee for access to the MIT Nu Plasma II and J. DesOrmeau for the scanning electron microscopy imaging at U. Nevada in Reno. We thank E. Bloch and M. Méheut for comments to an earlier version of the manuscript. G. Gaetani, H. Marshall, and three anonymous reviewers provided comments that greatly helped improve the manuscript. \n\nFunding: This research was supported by NSF-EAR grants 1823748 (to M.I.-M.) and 1824002 (to F.L.H.T.), and startup funds to M.I.-M. provided by U. Rochester. \n\nAuthor contributions: M.I.-M. and F.L.H.T. designed the study, developed all laboratory methods, performed the measurements, interpreted the results, and wrote the manuscript. \n\nThe authors declare that they have no competing interests. \n\nData and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Aliquots from rock and mineral samples used in this study are stored at U. Rochester and available from M.I.-M. upon request.", revision_no = "11", abstract = "Zirconium is a commonly used elemental tracer of silicate differentiation, yet its stable isotope systematics remain poorly known. Accessory phases rich in Zr⁴⁺ such as zircon and baddeleyite may preserve a unique record of Zr isotope behavior in magmatic environments, acting both as potential drivers of isotopic fractionation and recorders of melt compositional evolution. To test this potential, we measured the stable Zr isotope composition of 70 single zircon and baddeleyite crystals from a well-characterized gabbroic igneous cumulate. We show that (i) closed-system magmatic crystallization can fractionate Zr stable isotopes at the >0.5% level, and (ii) zircon and baddeleyite are isotopically heavy relative to the melt from which they crystallize, thus driving chemically differentiated liquids toward isotopically light compositions. Because these effects are contrary to first-order expectations based on mineral-melt bonding environment differences, Zr stable isotope fractionation during zircon crystallization may not solely be a result of closed-system thermodynamic equilibrium.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/98640, title ="Nucleosynthetic, radiogenic and stable strontium isotopic variations in fine- and coarse-grained refractory inclusions from Allende", author = "Charlier, B. L. A. and Tissot, F. L. H.", journal = "Geochimica et Cosmochimica Acta", volume = "265", pages = "413-430", month = "November", year = "2019", doi = "10.1016/j.gca.2019.09.005", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190913-095500320", note = "© 2019 Elsevier Ltd. \n\nReceived 16 September 2018, Accepted 4 September 2019, Available online 12 September 2019. \n\nWe thank Greg Brennecka, Glenn MacPherson and two anonymous reviewers for their thorough and incisive reviews which helped clarify our presentation and thinking. We also thank Qing-zhu Yin for his comments and Jeffrey Catalano for final editorial handling. This work was supported by a Crosby Postdoctoral Fellowships (MIT) and NSF grant (EAR1824002) to FT, and NASA grants NNX17AE86G (LARS), NNX17AE87G (Emerging Worlds), and 80NSSC17K0744 (Habitable Worlds) to ND.", revision_no = "18", abstract = "We present new nucleosynthetic, radiogenic and stable Sr isotopic data from fifteen previously studied CAIs from the Allende CV3 meteorite, including the highly altered Curious Marie inclusion. We use double-spike TIMS techniques to determine the degrees of isotopic mass fractionation, and also present internally normalised data for the same sample digestions to permit comparisons with previous studies and couple these isotopic data with Rb, Sr, Eu and Th abundance data to consider the origins and relationships of the isotopic variations documented here. Analysed CAIs display elevated μ^(84)Sr anomalies of +58 ppm to +287 ppm, with variability far outside of analytical uncertainties (13 ppm 2 s.d.). We cannot tell at present whether these variations arise from heterogeneities in p-process ^(84)Sr or in the other non-radiogenic isotopes of Sr (^(86)Sr, ^(88)Sr) that are produced by the main s-process, weak s-process, and r-process. All inclusions fall on an offset mass-dependent fractionation line in three-isotope space (δ^(88/86)Sr vs δ^(84/86)Sr) identical within error to that previously defined by bulk undifferentiated meteorites, and have a total range of δ^(88/86)Sr of ∼5.3 ‰ (+1.67 ‰ to -3.67 ‰), reflecting kinetic isotope effects during partial condensation/evaporation and/or low-temperature alteration processes. CI-normalized Sr/Th ratios in our CAIs correlate with normalized Eu/Th ratios with a ∼1:1 relationship, regardless of texture or Sr-isotopic values. This indicates that Sr and Eu had similar condensation behaviors with Eu condensing as Eu^(2+) and having the same chemical behavior in minerals as Sr^(2+) under conditions relevant to CAI formation in the solar nebula. Rb/Th ratios are highly variable: fine-grained CAIs display elevated Rb/Th ratios, consistent with the introduction of Rb into the CAIs by alkali-rich secondary alteration fluids. The μ ^(84)Sr anomalies measured in our CAIs are similar (in magnitude) to those found in carbonaceous chondrites that formed in the outer part of the solar system. A way to reconcile this observation with the formation of CAIs near the Sun would be if the inventories of Sr and other refractory elements in carbonaceous chondrites are dominated by a cryptic refractory dust component (CRD) that was formed early and near the Sun, and was subsequently transported outwards to the carbonaceous chondrite-forming region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/98071, title ="^(238)U/^(235)U measurement in single-zircon crystals: implications for the Hadean environment, magmatic differentiation and geochronology", author = "Tissot, François L. H. and Ibanez-Mejia, Mauricio", journal = "Journal of Analytical Atomic Spectrometry", volume = "34", number = "10", pages = "2035-2052", month = "October", year = "2019", doi = "10.1039/c9ja00205g", issn = "0267-9477", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190821-095956243", note = "© 2019 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. \n\nThe article was received on 15 Jun 2019, accepted on 16 Jul 2019 and first published on 26 Jul 2019. \n\nThis work was supported by an NSF grant (EAR1824002) and Crosby Postdoctoral Fellowships (MIT) to FT and MI, a Chamberlin Postdoctoral Fellowship (University of Chicago) to PB, grants from NSF (PG EAR1444951 and CSEDI EAR1502591) and NASA (LARS NNX17AE86G, EW NNX17AE87G, and SSW NNX15AJ25G) to ND, an MIT Ferry Fund award and NSF award (EAR1439559) to DM, and a NASA (EW 80NSSC17K0773) grant to TG. \n\nAuthor contributions: FT, PB, MI and ND initiated the study; FT, PB and MI designed the research; TMH provided the Jack Hills zircons; FT and MI performed the research. FT performed the measurements on ND's and DM's instruments and analyzed the data (including modeling). FT, MI and PB interpreted the data. FT wrote the manuscript with contributions from all co-authors. \n\nData and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the ESI.† Additional data related to this paper may be requested from the authors.", revision_no = "21", abstract = "Owing to the challengingly small amounts of uranium (U) they contain, the isotopic composition (^(238)U/^(235)U) of single zircon grains has never been measured. Leveraging methods we designed for analysis of small sample amounts and modern MC-ICPMS instruments, we show that precise (±0.04 to ±0.25‰) single-zircon ^(238)U/^(235)U measurements are now possible. We report data for 31 single grains from the Jack Hills conglomerate, and 3 reference zircon localities (FC-1, R33 and Temora). Consistent with the reducing conditions implied by the small Ce anomalies of many Hadean zircon, Jack Hills grains display only small δ238U variations (from −0.60 to −0.12‰). The distribution is centered on the average chondritic and bulk continental crust value, arguing against the widespread existence of Oklo-type reactors in the early Earth. The subtle δ^(238)U variations in Jack Hills zircons are more plausibly explained by a small (∼0.10%) mass-dependent equilibrium isotope fractionation between at least one U-bearing accessory mineral and silicate melts, during magmatic differentiation under reducing conditions. In contrast, the large δ^(238)U difference between pooled titanite and pooled zircon fractions from the Fish Canyon Tuff sample suggests larger isotope effects during igneous fractional crystallization under oxidizing conditions (∼QFM+2), with preferential removal of ^(235)U from the melt and into zircon, and/or other accessory phases. We estimate that ∼50% of zircon dated by the CA-ID-TIMS method would be amenable to single-grain U isotope measurements, making this method widely applicable to future studies. This would enable (i) improvements in precision and accuracy of U–Pb and Pb–Pb dates, (ii) accurate investigation of U-series disequilibrium contribution to U–Pb discordance, and (iii) accurate re-evaluation of U decay constants.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/90395, title ="Controls of eustasy and diagenesis on the ^(238)U/^(235)U of carbonates and evolution of the seawater (^(234)U/^(238)U) during the last 1.4 Myr", author = "Tissot, François L. H. and Chen, Cindy", journal = "Geochimica et Cosmochimica Acta", volume = "242", pages = "233-265", month = "December", year = "2018", doi = "10.1016/j.gca.2018.08.022", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181024-132628441", note = "© 2018 Elsevier Ltd. \n\nReceived 19 January 2018, Accepted 10 August 2018, Available online 23 August 2018. \n\nFT thanks Anne M. Gothmann for valuable discussions and comments on an earlier version of the manuscript. The Field Museum (Chicago) is thanked for providing several carbonate samples. Constructive criticisms from Morten B. Andersen, Chris Holmden, one anonymous reviewer, and editor Claudine Stirling greatly helped improve the manuscript. This work was supported by grants from ACS (52964-ND2), NSF (EAR1502591 and EAR1444951) and NASA (NNX17AE86G, NNX17AE87G, and NNX15AJ25G) to ND, a Crosby Postdoctoral Fellowship to FT, and funding from NSERC Discovery and Accelerator grant (RGPIN-316500) to AB. \n\nAuthors Contributions: FT and ND initiated the project. FT designed the research. FT, BMG, MN, GH, CC and PKS performed the research. FT interpreted the data with inputs from ND, CC, AB and PKS. FT wrote the manuscript with contributions from all co-authors.", revision_no = "14", abstract = "Using a leaching protocol designed for the study of U isotopes in recent carbonates, we measured the U isotope composition, both ^(238)U/^(235)U and ^(234)U/^(238)U, of modern and ancient corals (n\u202f=\u202f6), a limestone and a dolostone, as well as 43 shallow-water carbonate sediments from the ODP Leg 166 Site 1009 drill core, on the slope of the Bahamas platform. Although bulk corals record the seawater δ^(238)U value within ±0.02‰, differences of up to 0.30‰ in the δ^(238)U of individual leachates suggest a control of the coral structure and a more positive ^(238)U/^(235)U ratio in the centers of calcification.\nThe drill core δ^(238)U data shows that the ^(238)U/^(235)U ratio of shallow-water carbonates is controlled mainly by (1) variations in sea-level through the mixing of different amounts of platform-derived sediments (with δ^(238)U ∼0.50–0.60‰ heavier than seawater) and pelagic sediments (with seawater-like δ^(238)U values), (2) authigenic U enrichment via pore-watercirculation and U reduction both on the platform and down to ∼5 m below the surface (mbsf) after deposition of the sediment, and, to a lesser extent, by (3) early diagenetic processes (i.e., carbonate dissolution and/or recrystallization) during sediment burial. The global effect of these processes leaves the δ^(238)U values of shallow-water carbonates offset relative to that of seawater by Δ_(Carbonates-SW)\u202f=\u202f+0.24\u202f±\u202f0.06‰ (95% CI, including all samples). This shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow-water platform, shelf and slope environments (i.e., most of the carbonate sedimentary record prior to the Mesozoic) to account for the average effect of carbonate diagenesis. Assuming that the ^(238)U/^(235)U ratio of carbonate platform sediments directly records the seawater ^(238)U/^(235)U ratio would underestimate the extent of ocean-seafloor anoxia by at least a factor 10. The rapid fluctuations in δ^(238)U values due to sea-level changes (i) is a factor that should be considered before interpreting δ^(238)U variations as reflecting changes in oceanic paleoredox conditions and (ii) reinforces the need for statistically meaningful data sets.\nThe δ(^(234)U) data suggest that the (^(234)U/^(238)U) ratio of the seawater has remained within ∼20‰ of the modern seawater value during the last 1–1.4 Myr. Furthermore, we find that small-scale (1–15‰) variations in seawater δ(^(234)U) mirror sea-level changes during the penultimate glacial-interglacial period (∼140 to ∼200\u202fka), thus confirming the record of lower δ(^(234)U)_(SW) during periods of low sea-level stand and expanding it to at least the last two glacial-interglacial events (i.e., ∼0.23\u202fMa). Such fluctuations in δ(^(234)U)_(initial) values should be taken into account when screening carbonate sediments U-Th ages on the basis of the initial (^(234)U/^(238)U) ratios of the samples.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87085, title ="Titanium isotopes and rare earth patterns in CAIs: Evidence for thermal processing and gas-dust decoupling in the protoplanetary disk", author = "Davis, Andrew M. and Zhang, Junjun", journal = "Geochimica et Cosmochimica Acta", volume = "221", pages = "275-295", month = "January", year = "2018", doi = "10.1016/j.gca.2017.07.032", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180613-152623011", note = "© 2017 Elsevier Ltd. \n\nReceived 25 February 2017, Accepted 19 July 2017, Available online 27 July 2017. \n\nThis paper is dedicated to the memory of Ernst Zinner, who, among his many accomplishments, was a pioneer in studying titanium isotope anomalies in CAIs and presolar grains. We thank Curtis Williams and an anonymous reviewer for their careful and constructive reviews. This work was supported by the U.S. National Aeronautics and Space Administration, through grants NNX09AG39G and NNX15AF78G to AMD and NNX12AH60G to ND, and by the U.S. National Science Foundation, through grant EAR1144429 to ND.", revision_no = "14", abstract = "Titanium isotopic compositions (mass-dependent fractionation and isotopic anomalies) were measured in 46 calcium-, aluminum-rich inclusions (CAIs) from the Allende CV chondrite. After internal normalization to ^(49)Ti/^(47)Ti, we found that ε^(50)Ti values are somewhat variable among CAIs, and that ε^(46)Ti is highly correlated with ε^(50)Ti, with a best-fit slope of 0.162 ± 0.030 (95% confidence interval). The linear correlation between ε^(46)Ti and ε^(50)Ti extends the same correlation seen among bulk solar objects (slope 0.184 ± 0.007). This observation provides constraints on dynamic mixing of the solar disk and has implications for the nucleosynthetic origin of titanium isotopes, specifically on the possible contributions from various types of supernovae to the solar system. Titanium isotopic mass fractionation, expressed as δ′^(49)Ti, was measured by both sample-standard bracketing and double-spiking. Most CAIs are isotopically unfractionated, within a 95% confidence interval of normal, but a few are significantly fractionated and the range δ′^(49)Ti is from ∼−4 to ∼+4. Rare earth element patterns were measured in 37 of the CAIs. All CAIs with significant titanium mass fractionation effects have group II and related REE patterns, implying kinetically controlled volatility fractionation during the formation of these CAIs.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87099, title ="Distinct ^(238)U/^(235)U ratios and REE patterns in plutonic and volcanic angrites: Geochronologic implications and evidence for U isotope fractionation during magmatic processes", author = "Tissot, François L. H. and Dauphas, Nicolas", journal = "Geochimica et Cosmochimica Acta", volume = "213", pages = "593-617", month = "September", year = "2017", doi = "10.1016/j.gca.2017.06.045", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-103635044", note = "© 2017 Elsevier Ltd. \n\nReceived 28 December 2016, Accepted 28 June 2017, Available online 8 July 2017. \n\nConstructive criticisms from Greg Brennecka, two anonymous reviewers, and editor Yuri Amelin greatly helped improve the manuscript. This work was funded by NSF (grants CSEDI EAR1502591 and Petrology and GeochemistryEAR1444951) and NASA (grants LARS NNX17AE86G, EW NNX17AE87G, and SSW NNX15AJ25G) to ND, NASA grant NNX16AD29G to TG, and a Crosby Postdoctoral Fellowship to FT. The Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum and P. Heck, the Museum National d’Histoire Naturelle (Paris) and the Smithsonian Institute are thanked for providing meteorite samples. G. Brennecka is thanked for providing REE, Th and U concentrations data for some angrites. \n\nAuthors Contributions: ND and FT designed the research; FT performed the research; FT, ND and TG interpreted the data and wrote the paper.", revision_no = "14", abstract = "Angrites are differentiated meteorites that formed between 4 and 11 Myr after Solar Systemformation, when several short-lived nuclides (e.g., ^(26)Al-^(26)Mg, ^(53)Mn-^(53)Cr, ^(182)Hf-^(182)W) were still alive. As such, angrites are prime anchors to tie the relative chronology inferred from these short-lived radionuclides to the absolute Pb-Pb clock. The discovery of variable U isotopic composition (at the sub-permil level) calls for a revision of Pb-Pb ages calculated using an “assumed” constant ^(238)U/^(235)U ratio (i.e., Pb-Pb ages published before 2009–2010). In this paper, we report high-precision U isotope measurement for six angrite samples (NWA 4590, NWA 4801, NWA 6291, Angra dos Reis, D’Orbigny, and Sahara 99555) using multi-collector inductively coupled plasma mass-spectrometry and the IRMM-3636 U double-spike. The age corrections range from −0.17 to −1.20 Myr depending on the samples. After correction, concordance between the revised Pb-Pb and Hf-W and Mn-Cr ages of plutonic and quenched angrites is good, and the initial (^(53)Mn/^(55)Mn)_0 ratio in the Early Solar System (ESS) is recalculated as being (7 ± 1) × 10^(−6) at the formation of the Solar System (the error bar incorporates uncertainty in the absolute age of Calcium, Aluminum-rich inclusions – CAIs). An uncertainty remains as to whether the Al-Mg and Pb-Pb systems agree in large part due to uncertainties in the Pb-Pb age of CAIs.\nA systematic difference is found in the U isotopic compositions of quenched and plutonic angrites of +0.17‰. A difference is also found between the rare earth element (REE) patterns of these two angrite subgroups. The δ^(238)U values are consistent with fractionationduring magmatic evolution of the angrite parent melt. Stable U isotope fractionation due to a change in the coordination environment of U during incorporation into pyroxene could be responsible for such a fractionation. In this context, Pb-Pb ages derived from pyroxenes fraction should be corrected using the U isotope composition measured in the same pyroxene fraction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87100, title ="In situ isotopic studies of the U-depleted Allende CAI Curious Marie: Pre-accretionary alteration and the co-existence of ^(26)Al and ^(36)Cl in the early solar nebula", author = "Tang, Haolan and Liu, Ming-Chang", journal = "Geochimica et Cosmochimica Acta", volume = "207", pages = "1-18", month = "June", year = "2017", doi = "10.1016/j.gca.2017.03.001", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-104655106", note = "© 2017 Elsevier Ltd. \n\nReceived 18 August 2016, Accepted 1 March 2017, Available online 18 March 2017. \n\nWe thank Yuri Amelin, Yunbin Guan, and Benjamin Jacobsen for comments on the manuscript. We are particularly grateful to Edward D. Young and Katelyn A. McCain for their help with simulations of the thermal evolution for the small planetesimals. We also thank Heng Yang for his assistance on contour maps. The Curious Marie sample from the Allende meteorite was provided by the Robert A. Pritzker Center for Meteoritics (Field Museum). Discussions with Alexander N. Krot, Benjamin Jacobsen, Edward D. Young, and Craig E. Manning are greatly appreciated. This work was supported by NASA Grant (NNX13AD13G) to K.D.M., and a Crosby Postdoctoral Fellowship to F.L.H.T. The UCLA ion microprobe facility is partially supported by a grant from the NSF Instrumentation and Facilities program.", revision_no = "16", abstract = "The isotopic composition of oxygen as well as ^(26)Al-^(26)Mg and ^(36)Cl-^(36)S systematics were studied in Curious Marie, an aqueously altered Allende CAI characterized by a Group II REEpattern and a large ^(235)U excess produced by the decay of short-lived ^(247)Cm. Oxygen isotopic compositions in the secondary minerals of Curious Marie follow a mass-dependent fractionation line with a relatively homogenous depletion in ^(16)O (Δ^(17)O of −8‰) compared to unaltered minerals of CAI components. Both Mg and S show large excesses of radiogenic isotopes (^(26)Mg∗ and ^(36)S∗) that are uniformly distributed within the CAI, independent of parent/daughter ratio. A model initial ^(26)Al/^(27)Al ratio [(6.2 ± 0.9) × 10^(−5)], calculated using the bulk Al/Mg ratio and the uniform δ^(26)Mg∗ ∼ +43‰, is similar to the canonical initial solar system value within error. The exceptionally high bulk Al/Mg ratio of this CAI (∼95) compared to other inclusions is presumably due to Mg mobilization by fluids. Therefore, the model initial ^(26)Al/^(27)Al ratio of this CAI implies not only the early condensation of the CAI precursor but also that aqueous alteration occurred early, when ^(26)Al was still at or near the canonical value. This alteration event is most likely responsible for the U depletion in Curious Marie and occurred at most 50 kyr after CAI formation, leading to a revised estimate of the early solar system ^(247)Cm/^(235)U ratio of (5.6 ± 0.3) × 10^(−5). The Mg isotopic composition in Curious Marie was subsequently homogenized by closed-system thermal processing without contamination by chondritic Mg. The large, homogeneous ^(36)S excesses (Δ^(36)S∗ ∼ +97‰) detected in the secondary phases of Curious Marie are attributed to ^(36)Cl decay (t_(1/2) = 0.3 Myr) that was introduced by Cl-rich fluids during the aqueous alteration event that led to sodalite formation. A model ^(36)Cl/^(35)Cl ratio of (2.3 ± 0.6) × 10^(−5) is calculated at the time of aqueous alteration, translating into an initial ^(36)Cl/^(35)Cl ratio of ∼1.7–3 × 10^(−5) at solar system birth. The Mg and S radiogenic excesses suggest that ^(26)Al and ^(36)Cl co-existed in the early solar nebula, raising the possibility that, in addition to an irradiation origin, ^(36)Cl could have also been derived from a stellar source.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87131, title ="Origin of uranium isotope variations in early solar nebula condensates", author = "Tissot, François L. H. and Dauphas, Nicolas", journal = "Science Advances", volume = "2", number = "3", pages = "Art. No. e1501400", month = "March", year = "2016", doi = "10.1126/sciadv.1501400", issn = "2375-2548", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-145133764", note = "© 2016, The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited. \n\nReceived for publication October 7, 2015. Accepted for publication January 12, 2016. \n\nWe thank P. Heck, J. Holstein, and the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum for providing some of the CAI samples; I. Steele for help in operating the SEM at the University of Chicago; and L. Dussubieux for help in operating the LA-ICPMS at the Field Museum. We are grateful to A. M. Davis and B. S. Meyer for discussions. \n\nThis work was supported by grants from NASA (Laboratory Analysis of Returned Samples, NNX14AK09G; Cosmochemistry, OJ-30381-0036A and NNX15AJ25G) and NSF (Petrology and Geochemistry, EAR144495; Cooperative Studies of the Earth’s Deep Interior, EAR150259) to N.D. and a NASA grant (Cosmochemistry, NNX13AE73G) to L.G. \n\nAuthor contributions: N.D. and F.L.H.T. designed the research; F.L.H.T. and L.G. selected the samples; F.L.H.T. performed the research; F.L.H.T., N.D., and L.G. wrote the paper. \n\nThe authors declare that they have no competing interests. \n\nData and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data are available from the authors upon request. This is Origins Lab contribution number 91.", revision_no = "18", abstract = "High-temperature condensates found in meteorites display uranium isotopic variations (^(235)U/^(238)U), which complicate dating the solar system’s formation and whose origin remains mysterious. It is possible that these variations are due to the decay of the short-lived radionuclide ^(247)Cm (t_(1/2) = 15.6 My) into ^(235)U, but they could also be due to uranium kinetic isotopic fractionation during condensation. We report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of ^(235)U reaching ~+6% relative to average solar system composition, which can only be due to the decay of ^(247)Cm. This allows us to constrain the ^(247)Cm/^(235)U ratio at solar system formation to (7.0 ± 1.6) × 10^(−5). This value provides new clues on the universality of the nucleosynthetic r-process of rapid neutron capture.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87122, title ="Spinel–olivine–pyroxene equilibrium iron isotopic fractionation and applications to natural peridotites", author = "Roskosz, Mathieu and Sio, Corliss K. I.", journal = "Geochimica et Cosmochimica Acta", volume = "169", pages = "184-199", month = "November", year = "2015", doi = "10.1016/j.gca.2015.07.035", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-140539393", note = "© 2015 Elsevier Ltd. \n\nReceived 5 December 2014, Accepted 27 July 2015, Available online 12 August 2015. \n\nWe thank Ian Steele (University of Chicago) for assistance in performing the electron probe analyses and Séverine Bellayer (UMET, ENSCL, Université Lille 1) for additional electron microprobe analysis. Jonathan Giencke (Bruker AXS) performed the XRD analysis. We thank Dr. X.M. Zhao for sharing her data on the peridotites from Yangyuan, North China Craton with us. The thoughtful reviews of three anonymous reviewers and the handling by S. Weyer deeply improved the quality of this work. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. This work was supported by an ANR grant (2011JS56 004 01; FrIHIDDA) to MR; grants from NSF Petrology and Geochemistry (EAR1144429), NASA Cosmochemistry (NNX12AH60G), LARS (NNX14AK09G) and FACCTS programs to ND; a Chateaubriand Fellowship to CKS.", revision_no = "12", abstract = "Eight spinel-group minerals were synthesized by a flux-growth method producing spinels with varying composition and Fe^(3+)/Fe_(tot) ratios. The mean force constants of iron bonds in these minerals were determined by synchrotron nuclear resonant inelastic X-ray scattering (NRIXS) in order to determine the reduced isotopic partition function ratios (β-factors) of these spinels. The mean force constants are strongly dependent on the Fe^(3+)/Fe_(tot) of the spinel but are independent, or weakly dependent on other structural and compositional parameters. From our spectroscopic data, it is found that a single redox-dependent calibration line accounts for the effects of Fe^(3+)/Fe_(tot) on the β-factors of spinels. This calibration successfully describes the equilibrium Fe isotopes fractionation factors between spinels and silicates (olivine and pyroxenes). Our predictions are in excellent agreement with independent determinations for the equilibrium Fe isotopic fractionations for the magnetite–fayalite and the magnetite–hedenbergite couples. Our calibration applies to the entire range of Fe^(3+)/Fe_(tot) ratios found in natural spinels and provides a basis for interpreting iron isotopic variations documented in mantle peridotites. Except for a few exceptions, most of the samples measured so far are in isotopic disequilibrium, reflecting metasomatism and partial melting processes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87088, title ="Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia", author = "Tissot, François L. H. and Dauphas, Nicolas", journal = "Geochimica et Cosmochimica Acta", volume = "167", pages = "113-143", month = "October", year = "2015", doi = "10.1016/j.gca.2015.06.034", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180613-154628264", note = "© 2015 Elsevier. \n\nReceived 24 October 2014; accepted in revised form 25 June 2015; available online 4 July 2015. \n\nAssociate editor: Yuri Amelin. \n\nFT thanks T.J. Ireland and P.R. Craddock, for their help with the MC-ICPMS; P.R. Craddock, M. Roskosz and R. Yokochi for providing some seawater and evaporite samples; and N.D. Greber for useful comments on an earlier version of the manuscript. Constructive criticisms from Greg Brennecka, an anonymous reviewer, and editor Yuri Amelin helped improve the manuscript. This work was supported by grants from the ACS Petroleum Research Fund (52964), NSF (EAR-1144429, EAR-1502591), and NASA (NNX12AH60G and NNX14AK09G) to ND. This is Origins Lab contribution number 87.", revision_no = "26", abstract = "The ^(238)U/^(235)U isotopic composition of uranium in seawater can provide important insights into the modern U budget of the oceans. Using the double spike technique and a new data reduction method, we analyzed an array of seawater samples and 41 geostandards covering a broad range of geological settings relevant to low and high temperature geochemistry. Analyses of 18 seawater samples from geographically diverse sites from the Atlantic and Pacific oceans, Mediterranean Sea, Gulf of Mexico, Persian Gulf, and English Channel, together with literature data (n = 17), yield a δ^(238)U value for modern seawater of −0.392 ± 0.005‰ relative to CRM-112a. Measurements of the uranium isotopic compositions of river water, lake water, evaporites, modern coral, shales, and various igneous rocks (n = 64), together with compilations of literature data (n = 380), allow us to estimate the uranium isotopic compositions of the various reservoirs involved in the modern oceanic uranium budget, as well as the fractionation factors associated with U incorporation into those reservoirs. Because the incorporation of U into anoxic/euxinic sediments is accompanied by large isotopic fractionation (Δ_(Anoxic/Euxinic-SW) = +0.6‰), the size of the anoxic/euxinic sink strongly influences the δ^(238)U value of seawater. Keeping all other fluxes constant, the flux of uranium in the anoxic/euxinic sink is constrained to be 7.0 ± 3.1 Mmol/yr (or 14 ± 3% of the total flux out of the ocean). This translates into an areal extent of anoxia into the modern ocean of 0.21 ± 0.09% of the total seafloor. This agrees with independent estimates and rules out a recent uranium budget estimate by Henderson and Anderson (2003). Using the mass fractions and isotopic compositions of various rock types in Earth’s crust, we further calculate an average δ^(238)U isotopic composition for the continental crust of −0.29 ± 0.03‰ corresponding to a ^(238)U/^(235)U isotopic ratio of 137.797 ± 0.005. We discuss the implications of the variability of the ^(238)U/^(235)U ratio on Pb–Pb and U–Pb ages and provide analytical formulas to calculate age corrections as a function of the age and isotopic composition of the sample. The crustal ratio may be used in calculation of Pb–Pb and U–Pb ages of continental crust rocks and minerals when the U isotopic composition is unknown.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87145, title ="Oxygen isotopes and high ^(26)Mg excesses in a U-depleted fine-grained Allende CAI", author = "Tang, H. and Liu, M-C.", journal = "Meteoritics and Planetary Science", volume = "50", number = "S1", pages = "5263", month = "August", year = "2015", issn = "1086-9379", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-084848532", note = "© 2015 Meteoritical Society. \n\nFirst published: 23 July 2015.", revision_no = "9", abstract = "CAIs are thought to be among the first solids formed in the early Solar System (ESS). As such, they are prime samples to study when (1) investigating ESS high-temperature processes, and (2) searching for evidence of short-lived radionu-clides at the time of formation of the SS. A recent systematic study of fine-grained CAIs characterized by a Group II REE pat-tern from Allende [1], found an extremely large ^(235)U excess (δ^(235)U >50 ‰ rel. to CRM-112a) in one sample: ME-3364 3.2. The discovery of this large ^(235)U excess provides definite evidence of the existence of live ^(247)Cm in the ESS, as previously suggested by [2]. In this study, we analyzed the oxygen isotope composi-tions and Al-Mg systematics of CAI ME-3364 3.2 to constrain the conditions of its formation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87118, title ="Reduced partition function ratios of iron and oxygen in goethite", author = "Blanchard, M. and Dauphas, N.", journal = "Geochimica et Cosmochimica Acta", volume = "151", pages = "19-33", month = "February", year = "2015", doi = "10.1016/j.gca.2014.12.006", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-133018006", note = "© 2014 Elsevier Ltd. Published by Elsevier Ltd. \n\nReceived 25 June 2014, Accepted 4 December 2014, Available online 15 December 2014. \n\nL. Paulatto is acknowledged for his technical support to the computational work. This work was performed using HPC resources from GENCI-IDRIS (Grant 2014-i2014041519). This work has been supported by the French National Research Agency (ANR, projects 11-JS56-001 “CrIMin” and 2011JS56 004 01 “FrIHIDDA”), grants from NSF (EAR 1144429) and NASA (NNX12AH60G). Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357.", revision_no = "12", abstract = "First-principles calculations based on the density functional theory (DFT) with or without the addition of a Hubbard U correction, are performed on goethite in order to determine the iron and oxygen reduced partition function ratios (β-factors). The calculated iron phonon density of states (pDOS), force constant and β-factor are compared with reevaluated experimental β-factors obtained from Nuclear Resonant Inelastic X-ray Scattering (NRIXS) measurements. The reappraisal of old experimental data is motivated by the erroneous previous interpretation of the low- and high-energy ends of the NRIXS spectrum of goethite and jarosite samples (Dauphas et al., 2012). Here the NRIXS data are analyzed using the SciPhon software that corrects for non-constant baseline. New NRIXS measurements also demonstrate the reproducibility of the results. Unlike for hematite and pyrite, a significant discrepancy remains between DFT, NRIXS and the existing Mössbauer-derived data. Calculations suggest a slight overestimation of the NRIXS signal possibly related to the baseline definition. The intrinsic features of the samples studied by NRIXS and Mössbauer spectroscopy may also contribute to the discrepancy (e.g., internal structural and/or chemical defects, microstructure, surface contribution). As for oxygen, DFT results indicate that goethite and hematite have similar β-factors, which suggests almost no fractionation between the two minerals at equilibrium.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87089, title ="Magma redox and structural controls on iron isotope variations in Earth's mantle and crust", author = "Dauphas, N. and Roskosz, M.", journal = "Earth and Planetary Science Letters", volume = "398", pages = "127-140", month = "July", year = "2014", doi = "10.1016/j.epsl.2014.04.033", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180613-154839717", note = "© 2014 Elsevier B.V. Published by Elsevier B.V. \n\nReceived 13 July 2013, Revised 15 April 2014, Accepted 21 April 2014, Available online 23 May 2014. \n\nN.D. thanks the NSF Petrology and Geochemistry (EAR1144429) and NASA Cosmochemistry (NNX12AH60G) programs for support. M.R. thanks the support of the French ANR program (2011JS56 004 01, FrIHIDDA). The EPMA facility in Lille is supported by the European Regional Development Fund (ERDF). Constructive criticisms by Elizabeth Cottrell, Sune Nielsen, an anonymous reviewer, and editor Bernard Marty helped improve the manuscript. Discussions with Andrew J. Campbell, Jennifer M. Jackson and Wenli Bi were greatly appreciated.", revision_no = "15", abstract = "The heavy iron isotopic composition of Earth's crust relative to chondrites has been explained by vaporization during the Moon-forming impact, equilibrium partitioning between metal and silicate at core–mantle-boundary conditions, or partial melting and magma differentiation. The latter view is supported by the observed difference in the iron isotopic compositions of MORBS and peridotites. However, the precise controls on iron isotope variations in igneous rocks remain unknown. Here, we show that equilibrium iron isotope fractionation is mainly controlled by redox (Fe^(3+)/Fe_(tot) ratio) and structural (e.g., polymerization) conditions in magmas. We measured, for the first time, the mean force constants of iron bonds in silicate glasses by synchrotron Nuclear Resonant Inelastic X-ray Scattering (NRIXS, also known as Nuclear Resonance Vibrational Spectroscopy – NRVS, or Nuclear Inelastic Scattering – NIS). The same samples were studied by conventional Mössbauer and X-ray Absorption Near Edge Structure (XANES) spectroscopy. The NRIXS results reveal a +0.2 to +0.4‰ equilibrium fractionation on ^(56)Fe/^(54)Fe ratio between Fe^(2+) and Fe^(3+) end-members in basalt, andesite, and dacite glasses at magmatic temperatures. These first measurements can already explain ∼1/3 of the iron isotopic shift measured in MORBs relative to their source. Further work will be required to investigate how pressure, temperature, and structural differences between melts and glasses affect equilibrium fractionation factors. In addition, large fractionation is also found between rhyolitic glass and commonly occurring oxide and silicate minerals. This fractionation reflects mainly changes in the coordination environment of Fe2+ in rhyolites relative to less silicic magmas and mantle minerals, as also seen by XANES. We provide a new calibration of XANES features vs. Fe^(3+)/Fe_(tot) ratio determinations by Mössbauer to estimate Fe^(3+)/Fe_(tot) ratio in situ in glasses of basaltic, andesitic, dacitic, and rhyolitic compositions. Modeling of magma differentiation using rhyolite-MELTS shows that iron structural changes in silicic magmas can explain the heavy iron isotopic compositions of granitoids and rhyolites. This study demonstrates that iron stable isotopes can help reveal planetary redox conditions and igneous processes. Other heterovalent elements such as Ti, V, Eu, Cr, Ce, or U may show similar isotopic variations in bulk rocks and individual minerals, which could be used to establish past and present redox condition in the mantles of Earth and other planets.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87096, title ="Introducing a Comprehensive Data Reduction and Uncertainty Propagation Algorithm for U‐Th Geochronometry with Extraction Chromatography and Isotope Dilution MC‐ICP‐MS", author = "Pourmand, Ali and Tissot, François L. H.", journal = "Geostandards and Geoanalytical Research", volume = "38", number = "2", pages = "129-148", month = "June", year = "2014", doi = "10.1111/j.1751-908X.2013.00266.x", issn = "1639-4488", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-083203813", note = "© 2013 The Authors.\n\n Geostandards and Geoanalytical Research © 2013 International Association of Geoanalysts. \n\nReceived 10 Jun 13 – Accepted 14 Oct 13. \n\nWe would like to thank Nicolas Dauphas for providing the CRM‐112A U metal reference material, IRMM3636a spike and his generous input on development of the code and the Monte Carlo simulation. We thank David McGee for providing us with the CCA3 speleothem. We are also grateful to Ted Zateslo, Lary Ball and Franco Marcantonio for their feedback on mass spectrometry and thank Aaron Pietruszka for providing the ^(229)Th spike. Hai Cheng and Larry Edwards's contributions were instrumental in the initial dating of the CC3 sample at UMN. The authors appreciate the constructive comments from the journal editor Jon Woodhead, Noah McLean and two other anonymous reviewers. This study was in part funded by NSF Grant #1103489.", revision_no = "26", abstract = "We present an open‐source algorithm in Mathematica application (Wolfram Research) with a transparent data reduction and Monte Carlo simulation of systematic and random uncertainties for U‐Th geochronometry by multi‐collector ICP‐MS. Uranium and thorium were quantitatively separated from matrix elements through a single U/TEVA extraction chromatography step. A rigorous calibrator‐sample bracketing routine was adopted using CRM‐112A and IRMM‐035 standard solutions, doped with an IRMM‐3636a ^(233)U/^(236)U ‘double‐spike’ to account for instrumental mass bias and deviations of measured isotope ratios from certified values. The mean of ^(234)U/^(238)U and ^(230)Th/^(232)Th in the standard solutions varied within 0.42 and 0.25‰ (permil) of certified ratios, respectively, and were consistent with literature values within uncertainties. Based on multiple dissolutions with lithium metaborate flux fusion, U and Th concentrations in USGS BCR‐2 CRM were updated to 1739 ± 2 and 5987 ± 50 ng g^(−1) (95% CI), respectively. The measurement reproducibility of our analytical technique was evaluated by analysing six aliquots of an in‐house reference material, prepared by homogenising a piece of speleothem (CC3A) from Cathedral Cave, Utah, which returned a mean age of 21483 ± 63 years (95% CI, 2.9‰). Replicate analysis of ten samples from CC3A was consistent with ages previously measured at the University of Minnesota by single‐collector ICP‐MS within uncertainties.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/43179, title ="Coupled molybdenum, iron and uranium stable isotopes as oceanic paleoredox proxies during the Paleoproterozoic Shunga Event", author = "Asael, Dan and Tissot, François L. H.", journal = "Chemical Geology", volume = "362", pages = "193-210", month = "December", year = "2013", doi = "10.1016/j.chemgeo.2013.08.003", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140102-131225387", note = "© 2013 Elsevier B.V. \n\nAccepted 4 August 2013; Available online 16 August 2013. \n\nThis work was supported by the International Continental Drilling Program, by NSF (EAR#0820676), EuropoleMer and IFREMER. We thank Lee Kump, Victor Melezhik, Aivo Lepland and Andrey Bekker for advice and support in this project and the FAR-DEEP drilling team for sample archiving. We thank Yoan Germain for technical support.", revision_no = "14", abstract = "The Paleoproterozoic Era was a time of remarkable importance in the redox evolution of Earth's atmosphere and oceans. Here, we present a multi-proxy study of Mo, U and Fe isotopes together with Fe speciation of black shales and siltstones from the upper Zaonega Formation of the Onega Basin in Karelia. We attempt to better understand oceanic redox conditions during the 2.05 Ga Shunga Event as the next step following the Great Oxidation Event (GOE) and the Lomagundi carbon isotope excursion Event.\nA cautious examination of the Fe speciation data shows that the studied section was deposited under dominantly euxinic conditions (anoxic and sulfidic) and that the lower part of the section experienced metamorphism through which pyrite was altered to pyrrhotite. During this episode, the system was closed with respect to Fe but not sulfur. The Mo and U isotopic compositions (corrected for detrital input) were not affected by the metamorphism and loss of S and are fairly uniform throughout the entire section. The Fe isotope compositions are exceptionally heavy in the lower part of the section (up to δ^(56)Fe_(IRMM-14) = 0.83‰) and become lighter towards the upper intervals, which also show significant [Mo] and [U] enrichments. We suggest that this pattern reflects changes in the position of the deposition site relative to the redox structure of the water column. The upper part was deposited within a locally euxinic portion of the basin where H_2S availability was highest, removal of Mo and U was more efficient and precipitated pyrite captured relatively non-fractionated dissolved Fe. In other words, quantitative uptake of Fe was favored. In contrast, the lower interval was deposited on the lower margin of a euxinic wedge where H_2S availability was lower, and removal of Mo and U was less efficient. Pyrite precipitation in this part of the water column reflected a more fractionated dissolved Fe reservoir due to more protracted, non-quantitative Fe uptake because of less efficient pyrite formation under lower sulfide conditions and greater access to the large oceanic pool of Fe. The U isotopic signal was corrected for detrital contribution giving compositions similar to the riverine input and suggesting that co-precipitation into carbonates was the main process of U removal at this time.\nWe estimate the Mo isotope composition of the contemporaneous ocean to be δ^(98)Mo_(SW) = 0.85 ± 0.21‰. This is the lowest value yet reported for the Proterozoic ocean, suggesting that the oceanic Mo cycle was dominated by euxinic and anoxic sinks with negligible Mo removal into oxic environments. Recent studies have proposed a sharp increase in ocean–atmosphere oxygen levels during the Lomagundi Event followed by a dramatic crash. Our results from black shales of the 2.05 Ga Shunga Event are consistent with a post-Lomagundi decrease in biospheric oxygen levels.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87093, title ="Teflon-HPLC: A novel chromatographic system for application to isotope geochemistry and other industries", author = "Ireland, T. J. and Tissot, F. L. H.", journal = "Chemical Geology", volume = "357", pages = "203-214", month = "October", year = "2013", doi = "10.1016/j.chemgeo.2013.08.001", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180613-164054048", note = "© 2013 Elsevier. \n\nReceived 7 February 2013, Revised 1 August 2013, Accepted 4 August 2013, Available online 16 August 2013. \n\nEditor: L. Reisberg. \n\nThe authors would like to thank Kevin Lynch and Richard Dojutrek of the University of Illinois at Chicago, as well as Helmut Krebs of the University of Chicago for their help and guidance with anything machine shop related. Marc-Alban Millet is also thanked for his help with the REE elution. This work greatly benefited from thorough reviews by T. Meisel and an anonymous reviewer, as well as from editorial remarks by L. Reisberg. This work was supported by NASA grant NNX12AH60G and by a fellowship from the Packard Foundation to N.D. Some of the features of this system are described in a U.S. Provisional Patent Application (No. 61843509).", revision_no = "17", abstract = "Traditional column chromatography techniques are restricted by several factors, including limitations on column length, resin grain size, elution time, and a general inability to slowly ramp up or down reagent concentrations along a gradient. Likewise, most existing high-performance liquid chromatography (HPLC) systems are not amenable to certain column chromatography techniques that require highly concentrated acids. \n\nHere, we outline the development of a Teflon HPLC (T-HPLC) system for application to a wide variety of chromatography problems. The primary factors that set the T-HPLC system apart from any currently available chromatography procedure are the following: 1) a fluid flow path enclosed entirely by Teflon, 2) fully automated elution schemes controlled by computer software, which allows for fresh mixing of reagents for each elution step, and fine scale gradient/ramp elutions, 3) temperature control of the entire system (up to 80 °C) for enhanced chemical separations and, 4) a modular design making the system easily adaptable to a variety of separation schemes. \n\nThe effectiveness of the T-HPLC system is tested on two column techniques that are of particular interest to the geochemistry/cosmochemistry communities. The first application involves the separation of Ni from Mg, which is required for high precision Ni isotopic studies and for investigating the abundance of the extinct ^(60)Fe radionuclide. The T-HPLC system greatly simplifies and improves upon the classical technique. In a single pass on an 80 cm long column, we achieve excellent separation of Ni from Mg, with a much improved time frame (10 h versus 70 h). The second application is the separation of the individual rare earth elements from each other. The isotopic compositions of the multi-isotopic REEs (La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb and Lu) may hold important information about nucleosynthetic processes, cosmic-ray exposure effects in meteorites and airless bodies, and mass fractionation effects. For this application, we also developed a computer simulation that uses experimentally determined partition coefficients to simulate an elution curve in order to optimize the actual column elution scheme. Overall, we were able to achieve excellent separation of the multi-isotopic REEs from each other. \n\nAlthough the two applications that we explore are in the fields of geochemistry/cosmochemistry, the modular design and adaptability make the T-HPLC system useful to a wide array of scientific fields and industries.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87124, title ="Introducing a comprehensive data reduction algorithm for high-precision U-Th geochronology with isotope dilution MC-ICP-MS", author = "Pourmand, Ali and Tissot, François L. H.", journal = "Mineralogical Magazine", volume = "77", number = "5", pages = "1992", month = "July", year = "2013", issn = "0026-461X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-141533776", note = "© 2013 The Mineralogical Society.", revision_no = "12", abstract = "Multi collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is being increasingly utilized for\nU-Th geochronology of carbonate deposits with comparable\nprecision to thermal ionization mass spectrometry (TIMS) [1,\n2]. While attention has been paid to propagation of\nuncertainties for U-Th-Pb analysis by TIMS and the isochron\ntechnique [3,4], a comprehensive data processing scheme is\nlacking for MC-ICP-MS. To address this need, we have\ndeveloped an algorithm in Mathematica application to allow\nfor step-by-step monitoring of the data reduction process. The program is flexible and affords the user easy control over input variables. Adjustments for background and spike isotope contributions, abundance sensitivity and instrumental mass bias are implemented through the code, followed by age calculation and propagation of uncertainties with Monte Carlo simulation. A rigorous standard bracketing procedure was adopted using Uranium (CRM-112A) and Th (IRMM-035) standard solutions, doped with IRMM-3636a ^(233)U/^(236)U “double-spike”, to account for deviations of isotope ratios from certificate values and improve accuracy. Following a single U/TEVA extraction chromatography step to separate U from Th, ten replicate ages from a speleothem in Cathedral Cave (CC), Utah showed excellent agreement (R^2 = 0.999) with results previously measured at the University of Minnesota by single collection ICP-MS [5]. The external reproducibility of our analytical technique was evaluated by analyzing six aliquots of an in-house standard, prepared by homogenizing a piece of the CC speleothem, which returned a mean age of 21468±120 y (2SD). A limited amount of the standard powder is available upon request for interlaboratory calibration. We have successfully dated 36 samples from caves in the Bahamas, the Dominican Republic and Iran.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87117, title ="Iron, zinc, magnesium and uranium isotopic fractionation during continental crust differentiation: The tale from migmatites, granitoids, and pegmatites", author = "Telus, Myriam and Dauphas, Nicolas", journal = "Geochimica et Cosmochimica Acta", volume = "97", pages = "247-265", month = "November", year = "2012", doi = "10.1016/j.gca.2012.08.024", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-130943917", note = "© 2012 Elsevier Ltd. \n\nReceived 27 September 2011, Accepted 14 August 2012, Available online 25 August 2012.\n\nWe thank Alfred T. Anderson for valuable assistance with mineral separation; Mark S. Ghiorso and Julia E. Hammer for assisting with the Melts calculations; Richard J. Walker for providing the Black Hills pegmatite samples. We also thank Francis Albarede and Philippe Telouk for the generous access to the Nu Plasma mass-spectrometer in Lyon for the Zn isotopic measurements. Drafts of this manuscript have benefitted from thoughtful comments by Alfred T. Anderson and Cin-Ty A. Lee. Comprehensive reviews by three anonymous referees helped improve the manuscript. This work was supported by NASA (NNX09AG59G, NNX12AH60G), NSF (EAR-0820807) and a Packard Fellowship to N.D., by NSF (EAR-0838227 and EAR-1056713) and Arkansas Space Grant Consortium (SW19002) to F.Z.T, and by NASA Grants (NNX12AD88G and NNX12AH70G) to F.M.", revision_no = "12", abstract = "The causes of some stable isotopic variations in felsic rocks are not well understood. In particular, the origin of the heavy Fe isotopic compositions (i.e., high δ^(56)Fe values, deviation in ‰ of the ^(56)Fe/^(54)Fe ratio relative to IRMM-014) of granites with SiO_2 > 70 wt.% compared with less silicic rocks is still debated. It has been interpreted to reflect isotopic fractionation during late stage aqueous fluid exsolution, magma differentiation, partial melting, or Soret (thermal) diffusion. The present study addresses this issue by comparing the Fe isotopic compositions of a large range of differentiated crustal rocks (whole rocks of migmatites, granitoids, and pegmatites; mineral separates) with the isotopic compositions of Zn, Mg and U. The samples include granites, migmatites and pegmatites from the Black Hills, South Dakota (USA), as well as I-, S-, and A-type granitoids from Lachlan Fold Belt (Australia). The nature of the protolith (i.e., I- or S-type) does not influence the Fe isotopic composition of granitoids. Leucosomes (partial melts in migmatites) tend to have higher δ^(56)Fe values than melanosomes (melt residues) indicating that partial melting of continental crust material can possibly fractionate Fe isotopes. No clear positive correlation is found between the isotopic compositions of Mg, U and Fe, which rules out the process of Soret diffusion in the systems studied here. Zinc isotopes were measured to trace fluid exsolution because Zn can easily be mobilized by aqueous fluids as chloride complexes. Pegmatites and some granitic rocks with high δ^(56)Fe values also have high δ^(66)Zn values. In addition, high-SiO_2 granites show a large dispersion in the Zn/Fe ratio that cannot easily be explained by magma differentiation alone. These results suggest that fluid exsolution is responsible for some of the Fe isotopic fractionation documented in felsic rocks and in particular in pegmatites. However, some granites with high δ^(56)Fe values have unfractionated δ^(66)Zn values and were presumably poor in fluids (e.g., A-type). For these samples, iron isotopic fractionation during magma differentiation is a viable interpretation. Equilibrium Fe isotopic fractionation factors between silicic melts and minerals remain to be characterized to quantitatively assess the role of fractional crystallization on iron isotopes in granitoids.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87084, title ="A general moment NRIXS approach to the determination of equilibrium Fe isotopic fractionation factors: Application to goethite and jarosite", author = "Dauphas, N. and Roskosz, M.", journal = "Geochimica et Cosmochimica Acta", volume = "94", pages = "254-275", month = "October", year = "2012", doi = "10.1016/j.gca.2012.06.013", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180613-152259137", note = "© 2012 Elsevier. \n\nReceived 14 November 2011, Accepted 21 June 2012, Available online 2 July 2012. \n\nAssociate editor: Edwin Schauble. \n\nWe thank C. Achilles for determination of particle sizes using XRD data. Discussions with W. Sturhahn, R.N. Clayton, R. Caracas, and T. Fujii regarding data reduction, background subtraction, and stable isotope fractionation were greatly appreciated. M. Meheut, V. Polyakov, A. Shahar, and Associate editor E. Schauble are thanked for their thoughtful reviews of the manuscript. This work was supported by NASA (NNX09AG59G), by NSF EAR Petrology and Geochemistry (EAR-1144429), and by a Packard Fellowship to N. Dauphas. L. Gao acknowledges the financial support from COMPRES under NSF Cooperative Agreement EAR 10-43050. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the US DOE under contract N° DE-AC02-06CH11367.", revision_no = "17", abstract = "The equilibrium Fe isotopic fractionation factors of goethite and jarosite have considerable importance for interpreting Fe isotope variations in low temperature aqueous systems on Earth and possibly Mars in the context of future sample return missions. We measured the β-factors of goethite FeO(OH), potassium-jarosite KFe_3(SO_4)_2(OH)_6, and hydronium-jarosite (H_3O)Fe_3(SO_4)_2(OH)_6, by Nuclear Resonant Inelastic X-ray Scattering (NRIXS, also known as Nuclear Resonance Vibrational Spectroscopy – NRVS or Nuclear Inelastic Scattering – NIS) at the Advanced Photon Source. These measurements were made on synthetic minerals enriched in ^(57)Fe. A new method (i.e., the general moment approach) is presented to calculate β-factors from the moments of the NRIXS spectrum S(E). The first term in the moment expansion controls iron isotopic fractionation at high temperature and corresponds to the mean force constant of the iron bonds, a quantity that is readily measured and often reported in NRIXS studies. The mean force constants of goethite, potassium-jarosite, and hydronium-jarosite are 314 ± 14, 264 ± 12, and 310 ± 14 N/m, respectively (uncertainties include statistical and systematic errors). The general moment approach gives ^(56)Fe/^(54)Fe β-factors of 9.7, 8.3, and 9.5‰ at 22 °C for these minerals. The β-factor of goethite measured by NRIXS is larger than that estimated by combining results from laboratory exchange experiments and calculations based on electronic structure theory. Similar issues have been identified previously for other pairs of mineral–aqueous species, which could reflect inadequacies of approaches based on electronic structure theory to calculate absolute β-factors (differences in β-factors between aqueous species may be more accurate) or failure of laboratory experiments to measure mineral–fluid equilibrium isotopic fractionation at low temperature. We apply the force constant approach to published NRIXS data and report 1000 × ln β for important Fe-bearing phases of geological and biochemical relevance such as myoglobin, cytochrome f, pyroxene, metal, troilite, chalcopyrite, hematite, and magnetite.", }