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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¹Tra-Mi Ho et al. (>10)
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105200]
¹German Aerospace Center (DLR), Institute of Space Systems, Robert-Hooke-Str. 7, 28359, Bremen, Germany

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¹Matthew E. Sanborn,¹Meenakshi Wadhwa
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13631]
¹School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, Arizona, 85287‐1404 USA
Published by arrangement with John Wiley & Sons

The angrites are a class of achondrites that encompass a wide range of igneous textures from quenched, volcanic, and subvolcanic stones to slowly cooled, plutonic rocks. The compositions of the various geochemical reservoirs generating this variety of rocks have not been investigated fully because historically the numbers and masses of angrites available for study have been quite small. However, the rapid increase in meteorites from Northwest Africa (NWA) has enabled a renewed opportunity for such an investigation. In particular, three samples, NWA 2999, 4590, and 4801, have provided a new window into our understanding of the origin and petrogenesis of the coarse‐grained (plutonic) angrites. We report here the trace element abundances in individual mineral grains of pyroxene, plagioclase, olivine/kirschsteinite, and phosphate and in the whole‐rock samples. We utilize these data to constrain the petrogenetic history of each of these samples on the angrite parent body (e.g., parental melt compositions and oxygen fugacity conditions) and assess genetic relationships to previously investigated angrites. The trace element abundances in each of the three coarse‐grained angrites studied here indicate a unique history for each. The observed trace element abundances and patterns in NWA 2999 show similarities with previously studied fine‐grained, volcanic angrites and potentially indicate a common geochemical source reservoir, even though NWA 2999 is temporally distinct from the volcanic angrites. In contrast, NWA 4590 has trace element characteristics analogous to other coarse‐grained angrites (e.g., Lewis Cliff [LEW] 86010), suggesting that these samples originated from geochemically similar source reservoirs. The third angrite, NWA 4801, exhibits geochemical characteristics most similar to the plutonic, coarse‐grained angrites, but also appears to have some affinities in its trace element characteristics to the volcanic, fine‐grained angrites. This suggests that NWA 4801 may represent a petrogenetic link between two distinct geochemical reservoirs on the angrite parent body. In aggregate, the trace element distributions in these three plutonic angrites suggest that while they may have originated up to several million years after the fine‐grained angrites, they sampled a range of source reservoirs on the angrite parent body. Some of these source reservoirs were likely similar to those of the fine‐grained angrites, but others had distinct geochemical characteristics.

¹L. Krämer Ruggiu,²P.Beck,¹J.Gattacceca,²J.Eschrig
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114393]
¹Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
²Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France
Copyrigh Elsevier

The composition of asteroids gives crucial insights into the formation and evolution of the Solar System. Although spectral surveys and spacecraft missions provide information on small bodies, many important analyses can only be performed in terrestrial laboratories. Meteorites represent our main source of samples of extraterrestrial material. Determining the source asteroids of these meteorites is crucial to interpret their analyses in the broader context of the inner Solar System. For now, the total number of parent bodies represented in our meteorites collection is estimated to about 150 parent bodies, of which 50 parent bodies represented by the poorly studied ungrouped chondrites. Linking ungrouped meteorites to their parent bodies is thus crucial to significantly increase our knowledge of asteroids. To this end, the petrography of 25 ungrouped chondrites and rare meteorite groups was studied, allowing grouping into 6 petrographic groups based on texture, mineralogy, and aqueous and thermal parent body processing. Then, we acquired visible-near-infrared (VIS-NIR) reflectance spectroscopy data of those 25 meteorites, in order to compare them to ground-based telescopic observations of asteroids. The reflectance spectra of meteorites were obtained on powdered samples, as usually done for such studies, but also on raw samples and polished sections. With asteroids surfaces being more complex than fine-grained regolith (e.g., asteroid (101955) Bennu), in particular near-Earth asteroids, the use of raw samples is a necessary addition for investigating parent bodies. Our results showed that sample preparation influences the shape of the spectra, and thus asteroid spectral matching, especially for carbonaceous chondrites. Overall, the petrographic groups defined initially coincide with reflectance spectral groups, with only few exceptions. The meteorite spectra were then compared with reference end-member spectra of asteroids taxonomy. We matched the 25 studied meteorites to asteroids types, using a qualitative match of the shape of the spectra, as well as a quantitative comparison of spectral parameters (bands positions, bands depths and slopes at 1 and 2 μm). We define links between some of the studied ungrouped chondrites and asteroid types that had no meteorite connection proposed before, such as some very primitive type 3.00 ungrouped chondrites to B-type or Cg-type asteroids. We also matched metamorphosed ungrouped carbonaceous chondrites to S-complex asteroids, suggesting that this complex is not only composed of ordinary chondrites or primitive achondrites, as previously established, but may also host carbonaceous chondrites. Conversely, some ungrouped chondrites could not be matched to any known asteroid type, showing that those are potential samples from yet unidentified asteroid types.