¹Jemma Davidson,¹Conel M.O’D.Alexander,²Rhonda M.Stroud,³Henner Busemann,¹Larry R.Nittler
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.032]
¹Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington DC, 20015-1305, USA
²Naval Research Laboratory Code 6366, 4555 Overlook Ave. SW, Washington, DC 20375, USA
³Institute of Petrology and Geochemistry, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
Copyright Elsevier

Here we report the relative degrees of thermal metamorphism for five Antarctic Ornans-like carbonaceous (CO) chondrites, including Dominion Range (DOM) 08006, as determined from the Cr-content of their FeO-rich (ferroan) olivine. These five CO3 chondrites complete the previously poorly-defined CO3.00 to 3.2 chondrite metamorphic trend. DOM 08006 appears to be a highly primitive CO chondrite of petrologic type 3.00. We report the detailed mineralogy and petrography of DOM 08006 using a coordinated, multi-technique approach.

The interchondrule matrix in DOM 08006 consists of unequilibrated mixtures of silicate, metal, and sulfide minerals and lacks Fe-rich rims on silicates indicating that DOM 08006 has only experienced minimal, if any, thermal metamorphism. This is also reflected by the Co/Ni ratios of Ni-rich and Ni-poor metal, a sensitive indicator of thermal metamorphism, and the presence of euhedral chrome-spinel grains, which typically become subhedral to anhedral during progressive metamorphism. DOM 08006 matrix shows minor evidence for aqueous alteration and while the presence of magnetite surrounding metal in chondrules indicates that there has been some interaction with fluid, much metal remains and none of the sulfides analyzed show evidence of being formed by aqueous alteration. Furthermore, the plagioclase of ∼50% of chondrules analyzed show resolvable excess silica indicating that these chondrules have experienced minimal, if any, reprocessing in the CO parent body.

Noble gas data for DOM 08006 show that it contains the highest concentrations of trapped ³⁶Ar and ¹³²Xe of all CO chondrites analyzed to date, further indicating that DOM 08006 is the most primitive CO chondrite known. The cosmic ray exposure age of DOM 08006 is estimated to be ∼19 Ma.

The minimally altered nature of DOM 08006 demonstrates that it is an extremely important sample for providing valuable insight into early Solar System conditions. At a total weight of 667 g, a significant amount of material is available for a wide array of future studies.

^1,2Adam R.Sarafian,^1,3Sune G.Nielsen,^3,4Horst R.Marschall,³Glenn A.Gaetani,⁵Kevin Righter,⁶Eve L.Berger
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.023]
¹NIRVANA Laboratories, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, USA
²Corning Research and Development Corporation, Corning, NY 14873
³Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, USA
⁴Institut für Geowissenschaften, Goethe Universtät Frankfurt, 60438 Frankfurt am Main, Germany
⁵NASA-JSC, Mailcode XI2, 2101 NASA Pkwy, Houston, TX 77058, USA
⁶GeoControl Systems Inc. – Jacobs JETS Contract –NASA JSC, USA
Copyright Elsevier

The processes that controlled accretion of water and volatiles to the inner solar system remain enigmatic, because it is difficult to determine the absolute concentrations of volatile elements in planetary bodies. In this contribution we study rare unequilibrated eucrites derived from the asteroid 4 Vesta, to determine the water and fluorine content of this asteroid by measuring the volatile content of pyroxene. Common thermal metamorphism in most equilibrated eucrites would have diffusively reset magmatic volatile contents. The unequilibrated eucrites are, therefore, the most suitable samples to determine primary magmatic volatile contents of 4 Vesta. We find H₂O and F contents in pyroxenes of 4–11 µg/g and 0.12–0.23 µg/g. We also determine a H₂O partition coefficient for clinopyroxene and melt equilibrated at 0.1 MPa of D_H2O = 0.1, which is higher than values previously reported for higher pressures. The higher compatibility of H₂O in this experiment could partially be due to high OH/H₂O ratio at the low total water contents in this experimental charge, but only further more detailed experiments will fully delineate the reasons for the more compatible behavior for water at lower pressures. However, given the lack of H₂O partitioning data at low pressures we conclude that our 0.1 MPa experiment is the most appropriate to calculate magmatic water contents for melt in equilibrium with eucrite pyroxene. After using appropriate partition coefficients we calculate melt concentrations of 50–70 µg/g H₂O and 1.5–2.4 µg/g F. In turn, these are converted into bulk 4 Vesta water and F contents of 10–70 µg/g H₂O and 0.3–2 µg/g F by assuming eucrite formation via either mantle partial melting or extraction from a magma ocean. We also measure the D/H of the clinopyroxenes and show that these are identical to the results of previous studies that reported D/H in eucrite apatite. These values match those found in carbonaceous chondrites suggesting that water in 4 Vesta accreted from carbonaceous chondrites and not from cometary material.

^1,2Gokce Ustunisik,^2,3Denton S.Ebel,^3,2David Walker,^4,1Roger L.Nielsen,^3,2Marina Gemma
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.038]
¹Department of Geology and Geological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, 57701
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, 10024-5192
³Department of Earth and Environmental Sciences, Lamont Doherty Earth Observatory of Columbia University, Palisades, NY, 10964-8000
⁴104 CEOAS Admin, College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331
Copyright Elsevier

We determined the mineral-melt partition coefficients (D_i’s) and the compositional and/or temperature dependency between grossite, melilite, hibonite, olivine and Ca-, Al-inclusion (CAI)-type liquids for a number of light (LE), high field strength (HFSE), large ion lithophile (LILE), and rare earth (REE) elements including Li, Be, B, Sr, Zr, Nb, Ba, La, Ce, Eu, Dy, Ho, Yb, Hf, Ta, Th. A series of isothermal crystallization experiments was conducted at 5 kbar pressure and IW+1 in graphite capsules. The starting compositions were selected based on the calculated and experimentally confirmed phase relations during condensation in CI dust-enriched systems (Ebel and Grossman, 2000, Ebel, 2006, Ustunisik et al., 2014).

The partition coefficients between melt and gehlenite, hibonite, and grossite show that the trace element budget of igneous CAIs is controlled by these three major Al-bearing phases in addition to pyroxene. In general, LE, LILE, REE, and HFSE partition coefficients (by mass) decrease in the order of ^{Gehlenite-Melt}D_i > ^{Hibonite-Melt}D_i > ^{Grossite-Melt}D_i. The partition coefficients between gehlenitic melilite and CAI melt are approximately Be:0.14, B:0.07, Sr:0.79, Zr:0.02, Nb:0.01-0.02, Ba:0.05, La:1.03-3.44, Ce:1.2-3.86, Eu:1.19-2.88, Dy:1.14-3.23, Ho:1.04-2.91, Yb:0.7-1.70, Hf:0.02, Ta:0.01-0.02, Th:0.31-1.71. These results suggest that ^{Gehlenite-Melt}D_i vary by a factor of 2-3 in different melt compositions at the same T (∼1500 ^oC). ^{Hibonite-Melt}D_i exhibit a range as Be:0.02-0.04, B:0.01, Sr:0.21-0.66, Zr:0.02-0.18, Nb:0.03-0.05, Ba:0.02-0.06, La:0.56-4.38, Ce:0.52-3.54, Eu: 0.33-0.84, Dy: 0.25-0.32, Ho:0.17-0.29, Yb:0.05-0.19, Hf:0.05-0.38, Ta:0.02, Th:0.31-1.71. Increased Al and Ca, relative to earlier work, increases the compatibility of ^{Gehlenite-Melt}D_i , and also the compatibility of ^{Hibonite-Melt}D_i, especially for La and Ce.^{Grossite-Melt}D_i of individual mineral-melt pairs are Be:0.43, Sr:0.31, Zr:0.09, Nb:0.01, Ba:0.03, La:0.06, Ce:0.07, Eu:0.13, Dy:0.04, Ho:0.04, Yb:0.03, Hf:0.01, Ta:0.01, Th:0.01 for #18 at 1550 ^oC and as Sr:0.29, Nb:0.03, La:0.07, Ce:0.09, Eu:0.10, Dy:0.05, Ho:0.04, Yb:0.02, Hf:0.003, Ta:0.02, Th:0.02 for #7 at 1490 ^oC.

Olivine partitioning experiments confirm that olivine contribution to the trace element budget of CAIs is small due to the low ^Olivine-MeltD_i at a range of temperatures while ^Olivine-MeltD_{Eu, Yb} are sensitive to changes in T and fO₂. The development of a predictive model for partitioning in CAI-type systems would require more experimental data and use of analytical instruments capable of obtaining single phase analyses for crystals < 5µm.

¹Timothy J.McCoy,¹Catherine M.Corrigan,²Tamara L.Dickinson,³Gretchen K.Benedix,⁴Devin L.Schrader,⁴Jemma Davidson
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125536https://doi.org/10.1016/j.chemer.2019.125536]
¹Dept. of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560-0119, USA
²Science Matters Consulting, LLC, Washington, DC, 20016, USA
³School of Earth and Planetary Sciences, Curtin University, Bentley, WA, 6102, Australia
⁴Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287-1404, USA
Copyright Elsevier

Although acapulcoites and lodranites played a key role in understanding partial differentiation of asteroids, the lack of samples of the chondritic precursor limits our understanding of the processes that formed these meteorites. Grove Mountains (GRV) 020043 is a type 4 chondrite, with abundant, well-delineated, pyroxene-rich chondrules with an average diameter of 690 μm, microcrystalline mesostasis, polysynthetically striated low-Ca pyroxene, and slightly heterogeneous plagioclase compositions. GRV 020043 shows that evidence of partial melting is not an essential feature for classification within the acapulcoite-lodranite clan. GRV 020043 suggests a range of peak temperatures on the acapulcoite-lodranite parent body similar to that of ordinary chondrites, but shifted to higher temperatures, perhaps consistent with earlier accretion. Similarities in mineralogy, mineral composition, and oxygen isotopic composition link GRV 020043 to the acapulcoite-lodranite clan. These features include a high low-Ca pyroxene to olivine ratio, high kamacite to taenite ratio, and relatively FeO-poor mafic silicates (Fa_10.3, Fs_10.4) relative to ordinary chondrites, as well as the presence of ubiquitous metal and sulfide inclusions in low-Ca pyroxene and ƒO₂ typical of acapulcoites. GRV 020043 experienced modest thermal metamorphism similar to type 4 ordinary chondrites. The mineralogy and mineral compositions of GRV 020043, despite modest thermal metamorphism, suggests that most features of acapulcoites previously attributed to reduction were, instead, inherited from the precursor chondrite. Although partial melting was widespread on the acapulcoite-lodranite parent body, ubiquitous Fe,Ni-FeS blebs in the cores of silicates were not implanted by shock or trapped during silicate melting, but were inherited from the precursor chondrite with subsequent overgrowths during metamorphism.

^1,2Libourel, G.,³Nakamura, A.M.,⁴Beck, P.,⁴Potin, S.,⁵Ganino, C.,⁶Jacomet, S.,³Ogawa, R.,⁷Hasegawa, S.,¹Michel, P.
Science Advances 5, eaav3971 Link to Article [DOI: 10.1126/sciadv.aav3971]
¹Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, CS 34229, Nice Cedex 4, 06304, France
²Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96821, United States
³Graduate School of Science, Kobe University, 1-1 Rokkoudai-cho, Nada-ku, Kobe, 657-8501, Japan
⁴UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041, France
⁵Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Géoazur, 250 rue Albert Einstein, Sophia-Antipolis, Valbonne, 06560, France
⁶MINES Paristech, PSL-Research University, CEMEF-Centre de Mise en Forme des Matériaux, Centre for Material Forming, CNRS UMR 7635, CS 10207, 1 rue Claude Daunesse, Sophia-Antipolis Cedex, 06904, France
⁷Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, 252-5210, Japan

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^1,2Creech, J.B.,^1,3Moynier, F.,^4,5Koeberl, C.
Chemical Geology 528, 119279 Link to Article [DOI: 10.1016/j.chemgeo.2019.119279]
¹Institut de Physique du Globe de Paris, Université de Paris, 1 Rue Jussieu, Paris cedex 05, 75328, France
²Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia
³Institut Universitaire de France, Paris, 75005, France
⁴Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria
⁵Natural History Museum, Burgring 7, Vienna, 1010, Austria

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^1,2M. E. I. RIEBE,¹H. BUSEMANN,²C. M. O’D. ALEXANDER,²L. R. NITTLER,³C. D. K. HERD,¹C. MADEN,²J. WANG,¹R. WIELER
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13383]
¹Institute of Geochemistry and Petrology, ETH Zurich, CH-8092, Zurich, Switzerland
²DTM, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington, District of Columbia 20015, USA
³Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
Published by arrangement with John Wiley & Sons

Effects of aqueous alteration on primordial noble gas carriers were investigated by analyzing noble gases and determining presolar SiC abundances in insoluble organic matter (IOM) from four Tagish Lake meteorite (C2-ung.) samples that experienced different degrees of aqueous alteration. The samples contained a mixture of primordial noble gases from phase Q and presolar nanodiamonds (HL, P3), SiC (Ne-E[H]), and graphite (Ne-E[L]). The second most altered sample (11i) had a ~2–3 times higher Ne-E concentration than the other samples. The presolar SiC abundances in the samples were determined from NanoSIMS ion images and 11i had a SiC abundance twice that of the other samples. The heterogeneous distribution of SiC grains could be inherited from heterogeneous accretion or parent body alteration could have redistributed SiC grains. Closed system step etching (CSSE) was used to study noble gases in HNO3-susceptible phases in the most and least altered samples. All Ne-E carried by presolar SiC grains in the most altered sample was released during CSSE, while only a fraction of the Ne-E was released from the least altered sample. This increased susceptibility to HNO3 likely represents a step toward degassing. Presolar graphite appears to have been partially degassed during aqueous alteration. Differences in the 4He/36Ar and 20Ne/36Ar ratios in gases released during CSSE could be due to gas release from presolar nanodiamonds, with more He and Ne being released in the more aqueously altered sample. Aqueous alteration changes the properties of presolar grains so that they react similar to phase Q in the laboratory, thereby altering the perceived composition of Q.

¹A. GARENNE,^1,2P. BECK,³G. MONTES-HERNANDEZ,¹L. BONAL,¹E. QUIRICO,⁴O. PROUX,⁵J.L. HAZEMANN
Meteoritics & Planetary Science (In Press) Link to Article [doi: 10.1111/maps.13377]
¹CNRS, IPAG, Universite Grenoble Alpes, F-38000 Grenoble, France ²Institut Universitaire de France, Paris, France
³Institut des Sciences de la Terre (IsTERRE), Universite Grenoble Alpes/CNRS-INSU, Grenoble, France
⁴Observatoire des Sciences de l’Univers de Grenoble (OSUG) CNRS UMS 832, 414 rue de la piscine, 38400 Saint Martin d’Heres, France
⁵CNRS, Institut Neel, Universite Grenoble Alpes, 25 av. des Martyrs, 38042 Grenoble, France
Published by arrangement with John Wiley & Sons

The valence of iron has been used in terrestrial studies to trace the hydrolysis of primary silicate rocks. Here, we use a similar approach to characterize the secondary processes, namely thermal metamorphism and aqueous alteration, that have affected carbonaceous chondrites. X-ray absorption near-edge structure spectroscopy at the Fe-Kedge was performed on a series of 36 CM, 9 CR, 10 CV, and 2 CI chondrites. While previous studies have focused on the relative distribution of Fe0 with respect to oxidized iron (Feox = Fe2+ + Fe3+) or the iron distribution in some specific phases (e.g., Urey–Craig diagram; Urey and Craig 1953), our measurements enable us to assess the fractions of iron in each of its three oxidation states: Fe0, Fe2+, and Fe3+. Among the four carbonaceous chondrites groups studied, a correlation between the iron oxidation index (IOI = [2 (Fe2+) + 3(Fe3+)]/[FeTOT]) and the hydrogen content is observed. However, within the CM group, for which a progressive alteration sequence has been defined, a conversion of Fe3+ to Fe2+ is observed with increasing degree of aqueous alteration. This reduction of iron can be explained by an evolution in the mineralogy of the secondary phases. In the case of the few CM chondrites that experienced some thermal metamorphism, in addition to aqueous alteration, a redox memory of the aqueous alteration is present: a significant fraction of Fe3+ is present, together with Fe2+ and sometimes Fe0. From our data set, the CR chondrites show a wider range of IOI from 1.5 to 2.5. In all considered CR chondrites, the three oxidation states of iron coexist. Even in the least-altered CR chondrites, the fraction of Fe3+ can be high (30% for MET 00426). This observation confirms that oxidized iron has been integrated during formation of fine-grained amorphous material in the matrix (Le Guillou and Brearley 2014; Le Guillou et al. 2015; Hopp and Vollmer 2018). Last, the IOI of CV chondrites does not reflect the reduced/oxidized classification based on metal and magnetite proportions, but is strongly correlated with petrographic types. The valence of iron in CV chondrites therefore appears to be most closely related to thermal history, rather than aqueous alteration, even if these processes can occur together (Krot et al. 2004; Brearley and Krot 2013).

^1,2Celia Dalou,²Marc M.Hirschmann,³Steven D.Jacobsen,⁴CharlesLe Losq
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.029]
¹Centre de Recherches Pétrographiques et Géochimiques, 15 rue Notre-Dame des Pauvres, BP20, 54501 Vandoeuvre-lès-Nancy Cedex, France
²Dept. of Earth Sciences, 108 Pillsbury Hall, University of Minnesota, Minneapolis, MN 55455, USA
³Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, United States
⁴Research School of Earth Sciences, The Australian National University, Building 142, Mills Road, Canberra, ACT 2601, Australia
Copyright Elsevier

To better understand the solution of volatile species in a reduced magma ocean, we identify via Raman spectroscopy the nature of C-O-H-N volatile species dissolved in a series of reduced basaltic glasses. The oxygen fugacity (ƒ_O2) during synthesis varied from highly reduced at two log units below the iron-wustite buffer (IW-2.1) to moderately reduced (IW-0.4), spanning much of the magmatic ƒ_O2 conditions during late stages of terrestrial accretion. Raman vibrational modes for H₂, NH₂^–, NH₃, CH₄, CO, CN^–, N₂, and OH^– species are inferred from band assignments in all reduced glasses. The integrated area of Raman bands assigned to N₂, CH₄, NH₃ and H₂ vibrations in glasses increases with increasing molar volume of the melt, whereas that of CO decreases. Additionally, with increasing ƒ_O2, CO band areas increase while those of N₂ decrease, suggesting that the solubility of these neutral molecules is not solely determined by the melt molar volume under reduced conditions. Coexisting with these neutral molecules, other species as CN^–, NH₂^– and OH^– are chemically bonded within the silicate network. The observations indicate that, under reduced conditions, 1) H₂, NH₂^–, NH₃, CH₄, CO, CN^–, N₂, and OH^– species coexist in silicate glasses representative of silicate liquids in a magma ocean 2) their relative abundances dissolved in a magma ocean depend on melt composition, ƒ_O2 and the availability of H and, 3) metal-silicate partitioning or degassing reactions of those magmatic volatile species must involve changes in melt and vapor speciation, which in turn may influence isotopic fractionation.

^1,2Timothy T. BARROWS,³John MAGEE,⁴Gifford MILLER,⁵L. Keith FIFIELD
Meteoritics & Planetary Society (in Press) Link to Article [doi: 10.1111/maps.13378]
¹School of Earth and Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia
²Department of Geography, University of Portsmouth, Portsmouth PO1 2UP, UK
³Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 0200, Australia
⁴INSTAAR and Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA
⁵Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University, Canberra,Australian Capital Territory 2601, Australia
Published by arrangement with John Wiley & Sons

Wolfe Creek crater lies in northwestern Australia at the edge of the Great SandyDesert. Together with Meteor Crater, it is one of the two largest craters on Earth fromwhich meteorite fragments have been recovered. The age of the impact is poorly constrainedand unpublished data places the event at about 300,000 years ago. In comparison, MeteorCrater is well constrained by exposure dating. In this paper, we present new ages for WolfeCreek Crater from exposure dating using the cosmogenic nuclides10Be and26Al, togetherwith optically stimulated luminescence ages (OSL) on sand from a site created by theimpact. We also present a new topographic survey of the crater using photogrammetry. Theexposure ages range from~86 to 128 ka. The OSL ages indicate that the age of the impactis most likely to be~120 ka with a maximum age of 137 ka. Considering the geomorphicsetting, the most likely age of the crater is 1209 ka. Last, we review the age of MeteorCrater in Arizona. Changes in production rates and scaling factors since the original datingwork revise the impact age to 61.14.8 ka, or~20% older than previously reported.