¹Jean-Alix Barrata,²Marc Chaussidon,³Akira Yamaguchi,⁴Pierre Beck,⁵Johan Villeneuve,⁵David J. Byrne,⁵Michael W. Broadley,⁵Bernard Marty
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [https://doi.org/10.1073/pnas.2026129118]
¹Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzané, France;
²Institut de physique du globe de Paris, CNRS, Université de Paris, F-75005 Paris, France;
³National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan;
⁴CNRS, Institut de Planetologie et d’Astrophysique de Grenoble, F-38400 Saint Martin d’Hères, France;
⁵Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France

The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun’s photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.

¹Zachary A.Torrano,^1,2Devin L.Schrader,^1,2Jemma Davidson,^cRichard C.Greenwood,¹Daniel R.Dunlap,¹Meenakshi Wadhwa
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.03.004]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287, USA
²Center for Meteorite Studies, Arizona State University, Tempe, AZ, 85287, USA
³Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom
Copyright Elsevier

A close relationship between CM and CO chondrites has been suggested by previous petrologic and isotopic studies, leading to the suggestion that they may originate from similar precursor materials or even a common parent body. In this study, we evaluate the genetic relationship between CM and CO chondrites using Ti, Cr, and O isotopes. We first provide additional constraints on the ranges of ε50Ti and ε54Cr values of bulk CM and CO chondrites by reporting the isotopic compositions of CM2 chondrites Murchison, Murray, and Aguas Zarcas and the CO3.8 chondrite Isna. We then report the ε50Ti and ε54Cr values for several ungrouped and anomalous carbonaceous chondrites that have been previously reported to exhibit similarities to the CM and CO chondrite groups, including Elephant Moraine (EET) 83226, EET 83355, Grosvenor Mountains (GRO) 95566, MacAlpine Hills (MAC) 87300, MAC 87301, MAC 88107, and Northwest Africa (NWA) 5958, and the oxygen isotope compositions of a subset of these samples. We additionally report the ε50Ti, ε54Cr, and O isotopic compositions of additional ungrouped chondrites LaPaz Ice Field (LAP) 04757, LAP 04773, Lewis Cliff (LEW) 85332, and Coolidge to assess their potential relationships with known carbonaceous and ordinary chondrite groups. LAP 04757 and LAP 04773 exhibit isotopic compositions indicating they are low-FeO ordinary chondrites. The isotopic compositions of Murchison, Murray, Aguas Zarcas, and Isna extend the compositional ranges defined by the CM and CO chondrites in ε50Ti versus ε54Cr space. The majority of the ungrouped carbonaceous chondrites with documented similarities to the CM and/or CO chondrites plot outside the CM and CO group fields in plots of ε50Ti versus ε54Cr,Δ17O versus ε50Ti, and Δ17O versus ε54Cr. Therefore, based on differences in their Ti, Cr, and O-isotopic compositions, we conclude that the CM, CO, and ungrouped carbonaceous chondrites likely represent samples of multiple distinct parent bodies. We also infer that these parent bodies formed from precursor materials that shared similar isotopic compositions, which may indicate formation in regions of the protoplanetary disk that were in close proximity to each other.

¹Kei Shimizu,¹ConelM. O’D. Alexander,¹Erik H.Hauri,²Adam R.Sarafian,¹Larry R.Nittler,¹Jianhua Wang,³Steven D.Jacobsen,⁴Ruslan A.Mendybaev
Geochimica et Cosmochimica Acta (in Press) Link to Artiel [https://doi.org/10.1016/j.gca.2021.03.005]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC
²Science and Technology Division, Corning Incorporated, Corning, NY
³Dept. of Earth and Planetary Sciences, Northwestern University, Evanston, IL
⁴Dept. of Geophysical Sciences, University of Chicago, Chicago, IL
Copyright Elsevier

The partial pressures and isotopic compositions of volatiles present during chondrule formation can be constrained by the highly volatile element or HVE (H, C, F, Cl, and S) abundances and isotopic compositions in chondrules. Here we present the results of high spatial resolution and low background secondary ion mass spectroscopy (SIMS) analyses of the HVE concentrations and H isotopic compositions in type I and II chondrules in primitive ordinary chondrites Semarkona (LL3.00) and Queen Alexandra Range (QUE) 97008 (L3.05), and the primitive carbonaceous chondrite Dominion Range (DOM) 08006 (CO3.00). The HVEs in the chondrules primarily reside in the mesostases, in which the HVE contents and H isotopic compositions vary significantly (H2O: 8–10,200 ppm, CO2: 2.4–1170 ppm, F: 0.3–30 ppm, Cl: 0.07–175 ppm, S: 0.38–4400 ppm, δD: 77–15,000‰). To dissolve such HVE contents in a silicate melt requires significantly higher total pressures (up to 1900 bars), and in some cases requires anomalous gas compositions (CO dominated), compared to those expected from canonical conditions of chondrule formation (∼10-3 bars, H2+H2O dominated). Rather, the enrichments of H2O, CO2, Cl, and F in the mesostases at the edges of some chondrules suggest that there were secondary influxes of HVEs into the chondrule mesostases from the surrounding matrix during parent body processes. Consistent with this, melt inclusions sealed in olivine phenocrysts have significantly lower HVE contents than the mesostases in contact with the surrounding matrix material. Further, the calculated diffusion distances of H2O in silicate glasses under the relevant conditions are comparable to the radii of the chondrules. The high δD values in the mesostases could have been generated through isotopic Rayleigh fractionation as a result of the loss of very D-poor H2 generated from Fe metal oxidation by H2O in the parent bodies. Based on these results, we hypothesize that the bulk of the HVEs in the chondrules are secondary in origin. However, a small portion of the HVEs in chondrules could be primary, as there are low but measurable amounts of HVEs in the melt inclusions that are sealed in phenocrysts. Further, measured S contents in some chondrule mesostases agree with those predicted in a sulfide saturated silicate melt based on an experimentally calibrated thermodynamic model. We constrain the upper limits of primary HVEs in the chondrules based on the lowest measured HVE contents to minimize the effects of the secondary influx of HVEs (type I H2O: 7–11 ppm, CO2: 0.3–0.6 ppm, F: 0.1–0.2 ppm, Cl: 0.01–0.03 ppm, S: 0.3–60 ppm, and type II H2O: 50–85 ppm, CO2: 0.4–3 ppm, F: 0.04–2 ppm, Cl: 0.04–2 ppm, S: 190–260 ppm).

¹Ben Kumler,¹James M.D.Day
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.03.002]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
Copyright Elsevier

Eucrite meteorites are early-formed (>4.5 Ga) basaltic rocks that are likely to derive from the asteroid 4 Vesta, or a similarly differentiated planetesimal. To understand trace element and moderately volatile element (MVE) behavior more fully within and between eucrites, a laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) study is reported for plagioclase and pyroxene, as well as fusion crust and vitrophyric materials for ten eucrites. These eucrites span from a cumulate eucrite (Northwest Africa [NWA] 1923) to samples corresponding to Main Group (Queen Alexandra Range 97053, Pecora Escarpment 91245, Cumulus Hills 04049, Bates Nunatak 00300, Lewis Cliff 85305, Graves Nunataks 98098) and Stannern Group (Allan Hills 81001, NWA 1000) compositions, in addition to Elephant Moraine 90020. Along with a range of refractory trace elements, focus was given to abundances of five MVE (K, Zn, Rb, Cs, Pb) to interrogate the volatile abundance distributions in eucrite mineral phases. Modal recombination analyses of the eucrites reveals the important role of accessory phases (zircon, apatite) in some of the incompatible trace element (ITE) distributions, but not for the MVE which, for the phases that were analyzed, are mostly sited within plagioclase (Cs, Rb, K) and pyroxene (Zn, Pb), and are in equilibrium with a parental melt composition for Main Group eucrites. The new data reveal a possible relationship with total refractory ITE enrichment and texture, with the most ITE enriched Stannern Group eucrites examined (NWA 1000, ALHA 81001) having acicular textures and, in the case of ALHA 81001 a young degassing age (∼3.7 Ga). Collectively the results suggest that Stannern Group eucrites may be related to anatexis of the eucritic crust by thermal metamorphism, with the heat source possibly coming from impacts. Impact processes do not have a pronounced effect on the abundances of the MVE, where plagioclase, pyroxene, fusion crust, and whole rock compositions of eucrites are all significantly depleted in the MVE, with Zn/Fe, Rb/Ba and K/U similar to lunar rocks. Assessment of eucrite compositions, however, suggests that Vesta has a more heterogeneous distribution of volatile elements and is similarly to slightly less volatile-depleted than the Moon. Phase dependence of the MVE (e.g., Cl in apatite, Zn primarily into spinel and early formed phases, including pyroxene) is likely to influence comparison diagrams where MVE stable isotopes are shown. In the case of δ37Cl versus δ66Zn, metamorphism and impact processes may lead to a decrease in the δ37Cl value for a given δ66Zn value in eucrites, raising the possibility that late-stage impact and metamorphism had a profound effect on volatile distributions in early planetesimal crusts.

¹Morgan A. Cox,¹Aaron J. Cavosie,²Michael H. Poelchau,²Thomas Kenkmann,²Katarina Miljković,²Phil A. Bland
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13621]
¹Space Science and Technology Centre (SSTC), School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, 6102 Australia
²Institute of Earth and Environmental Sciences—Geology, Albert‐Ludwigs‐Universität (ALU) Freiburg, Albertstraße 23B, Freiburg, 79104 Germany
Published by arrangement with John Wiley & Sons

The distribution of shock deformation effects, as well as the structural expression of an impact structure, can be asymmetric, depending on target rock lithologies (e.g., layered versus homogenous), porosity of target rock, and angle of impact. Here, we present a detailed study of shock‐deformed quartz and zircon in silicified sandstones from the asymmetric Spider impact structure in Australia. We utilize optical microscopy and electron backscatter diffraction (EBSD) techniques in order to determine the spatial distribution of shock‐deformed zircon along a downrange transect across the central uplift of the structure, with the goal of constraining the physical distribution of shock effects created by an oblique impact. A total of 453 zircon grains from 12 samples of shatter cone‐bearing quartzite and breccia within the structure were surveyed for shock deformation by EBSD in situ within thin sections. Nineteen zircon grains contain {112} twins, including one grain with three twin orientations. Quartz grains from five samples along the transect were also surveyed using a universal stage in order to determine orientations of planar deformation features, planar fractures, and feather features, and to provide a baseline for comparison of data from zircon. The distribution of shocked zircon with {112} twins within the samples surveyed appears to be asymmetric relative to the center of the structure, in contrast to quartz, thus providing the first accessory mineral‐based evidence that supports an asymmetric distribution of shock deformation as a function of impact obliquity. Our results are an example where the highest intensity of observed shock deformation does not correspond to the geographic center of the structure, and may serve as a guide for field studies aimed at documenting the distribution of shock effects at other sites interpreted to result from oblique impacts.

^1,2Alan E. Rubin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13626]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California, 90095‐1567 USA
²Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, Maine, 04217 USA
Published by arrangement with John Wiley & Sons

For ordinary‐chondrite (OC) mass distributions, Benford’s law applies to the set of individual objects that survive intact on the Earth’s surface after atmospheric disruption of meteoroids. Among OCs, Antarctic finds conform more closely to Benford’s law than observed falls, Northwest Africa (NWA) finds, or Oman finds mainly because Antarctic OCs tend to be relatively unweathered (and mostly intact) and have not been aggregated as pairs under collective meteorite names. Deviations from Benford’s law can result from tampering with data sets. The set of OC falls reflects tampering with the original Benford distribution (produced by meteoroid disruption) by the deliberate aggregation of paired individual samples and inefficiencies in the collection of small samples. The sets of NWA and Oman OC finds have been affected by natural “tampering” of the original distributions principally by terrestrial weathering, which can cause sample disintegration. NWA finds were also affected by non‐systematic collection of samples influenced by commercial considerations; collectors preferred type‐3 OC as revealed by the high proportions of such specimens among NWA chondrites relative to those among falls and Oman and Antarctic finds. The percentage of type‐4 OC among falls is appreciably lower than in the sets of finds. This suggests that type‐4 chondrites are friable and disintegrate into numerous pieces; these are counted individually for the sets of finds, but collectively for falls. However, the fact that the percentages of type‐3 OC are not generally higher for finds may be that these samples tend to break into small pieces that are preferentially lost.

^1,2Yoko Kebukawa,³Sachio Kobayashi,²Noriyuki Kawasaki,¹Ying Wang,^2,3Hisayoshi Yurimoto,¹George D. Cody
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13629]
¹Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, District of Columbia, 20015 USA
²Department of Natural History Sciences, Hokkaido University, N10 W8, Sapporo, 060‐0810 Japan
³Isotope Imaging Laboratory, Creative Research Institution Sousei, Hokkaido University, N21 W10, Sapporo, 001‐0021 Japan
Published by arrangement with John Wiley & Sons

The large variations in hydrogen isotope ratios found in insoluble organic matter (IOM) in chondritic meteorites may be attributed to hydrogen isotopic exchange between IOM and water during aqueous alteration. We conducted D–H exchange experiments (1) during synthesis of IOM simulant (hereafter called chondritic organic analog, COA) from formaldehyde, glycolaldehyde, and ammonia with water, and (2) with the synthesized COA with a secondary reservoir of water. The changes in the D/H ratios obtained by infrared spectra of the COA suggest that most of the hydrogen in the COA is derived from water during synthesis. We further investigated the kinetics of D–H exchange between D‐rich COA and D‐poor water, as well as the opposite case, D‐poor COA and D‐rich water. To help assess understanding exchange kinetics, two‐dimensional isotope imaging obtained using isotope microscope revealed that no gradient D–H exchange profiles were present in the COA grains, indicating that the rate‐limiting step for D–H exchange is not diffusion. Thus, the changes in D/(D + H) ratios were fit by the first‐order reaction rate law. Apparent kinetic parameters—the rate constants, the activation energies, and the frequency factors—were obtained with the Arrhenius equation. Using these kinetic expressions, hydrogen isotopic exchange profiles were estimated for time and temperature behavior. The D–H exchange between organic matter and water is apparently relatively fast and this implies that the aqueous alteration temperatures should have been very low, likely close to 0 °C to maintain hydrogen isotopic disequilibrium between organic matter and liquid water for millions of years.

^1,2J.D.Tarnas,²J.F.Mustard,^2,3X.Wu²E.Das,^4,5K.M.Cannon,²C.B.Hundal,²A.C.Pascuzzo,^6,7J.R.Kellner,^5,8M.Parent
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114402]
¹NASA Jet Propulsion Laboratory, California Institute of Technology, United States of America
²Department of Earth, Environmental and Planetary Sciences, Brown University, United States of America
³National Space Science Center, Chinese Academy of Sciences, China
⁴Department of Geology and Geological Engineering, Colorado School of Mines, United States of America
⁵Space Resources Program, Colorado School of Mines, United States of America
⁶Institute at Brown for Environment and Society, Brown University, United States of America
⁷Department of Ecology and Evolutionary Biology, Brown University, United States of America
⁸Department of Electrical and Computer Engineering, University of Massachusetts at Amherst, United States of America
Copyright Elsevier

We designed a laboratory visible-to-near-infrared (VNIR) hyperspectral experiment to test the effectiveness of factor analysis/target transformation for detecting minerals mixed with Mars Global Simulant-1 (MGS-1). The purpose of this experiment is to test for true positive, true negative, false positive, and false negative results from application of factor analysis/target transformation methods and determine the parameters that dictate good versus bad algorithm performance. Gypsum, calcite, montmorillonite, nontronite, and kaolinite were each mixed with MGS-1 at abundances of 1%, 2.5%, 5%, 10%, 20%, and 50%. The mixtures were placed in 2.5 × 2.5 × 1 cm sample trays and imaged using a Headwall Imaging Spectrometer with a spectral range of 0.9–2.6 μm, 8.98 nm spectral sampling, and 0.34 mm/pixel spatial resolution. These images include thousands to tens of thousands of hyperspectral pixels covering each individual mixture tray. Full-image factor analysis/target transformation (FA/TT) and Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) were applied to these data to detect the minerals mixed with MGS-1. The results demonstrate that factor analysis/target transformation is prone to both false positive and false negative detections, but in certain applications—including DAFA/TT—it can be useful for highlighting spectrally interesting areas in hyperspectral images for follow-up investigation. The results presented here demonstrate that applications of factor analysis/target transformation to VNIR hyperspectral datasets should be used to highlight small outcrops and/or weak spectral signals in pixels for follow-up investigation. This emphasizes the need for supporting evidence to be obtained—in addition to factor analysis/target transformation—before interpretations of planetary surface processes should be made.

^1,2Krot, A.N.,¹Nagashima, K.,³Lyons, J.R.,⁴Lee, J.-E.,²Bizzarro, M.
Science Advances 6, eaay2724 Link to Article [DOI: 10.1126/sciadv.aay2724]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI, United States
²Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Denmark
³School of Earth and Space Exploration, Arizona State University, Tempe, AZ, United States
⁴Department of Astronomy and Space Science, School of Space Research, Kyung Hee University, South Korea

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¹C.Herny,²O.Mousis,³R.Marschall,¹N.Thomas ¹M.Rubin¹O.Pinzón-Rodríguez,⁴I.P.Wright
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105194]
¹Physikalisches Institut, Universität Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
²Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille, France
³Southwest Research Institute, 1050 Walnut St., Boulder, CO, 80302, USA
⁴Open University, School of Physical Sciences, Walton Hall, Milton Keynes MK7 6AA, Bucks, England

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