¹Keisuke Fukushi,^1,2Yasuhito Sekine,³Elizabeth B.Rampe
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.005]
¹Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192 Japan
²Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 Japan
³Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX77058, USA
Copyright Elsevier

Mars once possessed liquid water on its surface. In investigations of aqueous conditions on early Mars, the Mars Science Laboratory rover Curiosity has provided mineralogical and geochemical data from lacustrine sediments of Gale Crater, site of a former lake. Recently, the top-down method for quantitative reconstruction of the chemical parameters of ancient pore water, based on exchangeable cation compositions in smectite and secondary minerals, was developed and applied to the Yellowknife Bay sediments in Gale Crater. Here we report the application of this method to lacustrine sediment from the Quela drill site in Gale Crater, in the Karasburg member of the Murray formation. The results show that the final pore water to interact with the sediments had the following chemistry: pH = 3.6–5.6, Eh > 0.22 V, molality of Na ({Na}) = 0.14–2.2 mol/kg, {K} = 0.0080–0.31 mol/kg, {Ca} = 0.021–0.21 mol/kg, {Mg} < 0.14 mol/kg, {Fe(II)} < 0.063 mol/kg, {Cl} = 0.096–2.6 mol/kg and {SO4} = 0.048–0.33 mol/kg. At two adjacent drill sites (Marimba and Sebina), the comparable mineral assemblages and smectite interlayer compositions imply that they have water chemistry similar to that of the Quela sediment. The inferred pore water was undersaturated with respect to halite by an order of magnitude, although the sediment contains halite. This suggests that the final water in the Quela sediment disappeared by freezing and sublimation rather than evaporation. One interpretation of the high Na and Cl concentrations of the final pore water at Quela is that the sediment was deposited in an arid climate at around 3.5 Ga. The high salinity of the final pore water at Quela relative to that at Yellowknife Bay suggests that climate may have shifted from semi-arid when the Yellowknife Bay formation was deposited to arid when the Karasburg member was deposited. Alternatively, the high salinity at Quela suggests that the post-depositional fluids at 2–3 Ga was enriched in Na. In contrast to low Na in the post-depositional fluids in the underlying Yellowknife Bay, the high salinity of the post-depositional fluids of the Quela suggests different origin and/or timing of the re-wetting events between these two sites. The acidic pH and high Eh suggest that the Quela sediment was intensively affected by oxidizing and acidic post-depositional fluids. The pH of the final pore water would not have allowed the preservation of Ca and Mg carbonates under attainable CO2 partial pressures, which is consistent with the scenario of carbonate dissolution by acidic post-depositional fluids on Mars.

¹Bidong Zhang,²Nancy L.Chabot,^1,3Alan E.Rubin⁴Munir Humayun,⁵Joseph S.Boesenberg,⁶Deonvan Niekerk
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.004]
¹Department of Earth, Planetary & Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
³Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, ME 04217, USA
⁴National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, FL 32310, USA
⁵Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
⁶Department of Geology, Rhodes University, Makhanda 6140, South Africa
Copyright Elsevier

Group IIIF was established as a magmatic iron-meteorite group based on similar Ga and Ge abundances, unusually high Ga/Ge ratios, and the IIIAB-like interelement trends in its members; recent Mo and Ru isotopic data indicate that three of its members exhibit the isotopic signature of carbonaceous-chondrite (CC) irons. Here we report the elemental chemistry of this group and model its crystallization history. Included are new elemental data for IIIF irons acquired by both instrumental neutron activation analysis (INAA) and laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). A fractional-crystallization model was used to evaluate the IIIF compositional trends for 19 elements and was unable to explain the observed fractionation trends for several key elements (Co, Ga, Ge). In particular, the inability of this model to match Co in the IIIF irons is striking because (1) group IIIF has the widest Co variation among all magmatic iron groups and (2) none of the tested initial S contents (0−20 wt.%) explains both the wide Co variation and steep Co-As slope. Attempts to fit subsets of the IIIF irons were also unsuccessful. In addition, group IIIF has the greatest variety of structural classes and kamacite bandwidths among all established magmatic iron groups. If the IIIF irons constitute a coherent group, they were derived from a parent body that experienced more complex processes than simple fractional crystallization of the core.

The Zinder and Northwest Africa (NWA) 1911 pyroxene-bearing pallasites were recently suggested to be related to group IIIF based on their Ga and Ge contents, and we completed a petrographic study of the pallasite silicates and LA-ICP-MS analyses of their metal fractions. The two pallasites are related to one another: they have nearly identical mineralogical, elemental and O-isotopic compositions in their silicates and metals. Their metallic compositions resemble those of the IIIF irons Moonbi, St. Genevieve County, and Cerro del Inca, but their O-isotopic compositions resemble those of non-carbonaceous (NC) achondrites. Additional isotopic measurements are needed to test the potential genetic relationship to group IIIF.

^1,2Hu J.,²Sharp T.G.
Progress in Earth and Planetary Science 9, 6 Link to Article [DOI 10.1186/s40645-021-00463-2]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, CA, United States
²School of Earth and Space Exploration, Arizona State University, Tempe, 85287, AZ, United States

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¹Jean-Guillaume Feignon,^1,2Toni Schulz,³Ludovic Ferrière,⁴Steven Goderis,^4,5Sietze J.de Graaff,^4,5Pim Kaskes,^4,5Thomas Déhais,⁴Philippe Claeys,¹Christian Koeberl
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.006]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
²Institute for Geology und Mineralogy, University of Cologne, Zülpicher Strasse 49b, 50674 Cologne, Germany
³Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁴Research Unit: Analytical, Environmental & Geo-Chemistry, Department of Chemistry, Vrije Universiteit Brussel, AMGC-WE-VUB, Pleinlaan 2, 1050 Brussels, Belgium
⁵Laboratoire G-Time, Université Libre de Bruxelles, Av. F.D. Roosevelt 50, 1050 Brussels, Belgium
Copyright Elsevier

Constraining the degree of preservation of a meteoritic signature within an impact structure provides vital insights in the complex pathways and processes that occur during and after an impact cratering event, providing information on the fate of the projectile. The IODP-ICDP Expedition 364 drilling recovered a ∼829 m continuous core (M0077A) of impactites and basement rocks within the ∼200-km diameter Chicxulub impact structure peak ring. No highly siderophile element (HSE) data have been reported for any of the impact melt rocks of this drill core to date. Previous work has shown that most Chicxulub impactites contain less than 0.1% of a chondritic component. Only few impact melt rock samples in previous drill cores recovered from the Chicxulub might contain such a signal. Therefore, we analyzed impact melt rock and suevite samples, as well as pre-impact lithologies of the Chicxulub peak ring, with a focus on the HSE concentrations and Re–Os isotopic compositions.

Similar to the concentrations of the other major and trace elements, those of the moderately siderophile elements (Cr, Co, Ni) of impact melt rock samples primarily reflect mixing between a mafic (dolerite) and felsic (granite) components, with the incorporation of carbonate material in the upper impact melt rock unit (from 715.60 to 747.02 meters below seafloor). The HSE concentrations of the impact melt rocks and suevites are generally low (<39 ppt Ir, <96 ppt Os, <149 ppt Pt), comparable to the values of the average upper continental crust, yet three impact melt rock samples exhibit an enrichment in Os (125–410 ppt) and two of them also in Ir (250–324 ppt) by one order of magnitude relative to the other investigated samples. The 187Os/188Os ratios of the impact melt rocks are highly variable, ranging from 0.18 to 2.09, probably reflecting heterogenous target rock contributions to the impact melt rocks. The significant amount of mafic dolerite (mainly ∼20–60% and up to 80–90%) , which is less radiogenic (187Os/188Os ratio of 0.17), within the impact melt rocks makes an unambiguous identification of an extraterrestrial admixture challenging. Granite samples have unusually low 187Os/188Os ratios (0.16 on average), while impact melt rocks and suevites broadly follow a mixing trend between upper continental crust and chondritic/mantle material. Only one of the investigated samples of the upper impact melt rock unit could also be interpreted in terms of a highly diluted (∼0.01–0.05%) meteoritic component. Importantly, the impact melt rocks and pre-impact lithologies were affected by post-impact hydrothermal alteration processes, probably remobilizing Re and Os. The mafic contribution, explaining the least radiogenic 187Os/188Os values, is rather likely. The low amount of meteoritic material preserved within impactites of the Chicxulub impact structure may result from a combination of the assumed steeply-inclined trajectory of the Chicxulub impactor (enhanced vaporization, and incorporation of projectile material within the expansion plume), the impact velocity, and the volatile-rich target lithologies.

^1,2,3Mark C. Nottingham,⁴Finlay M. Stuart,⁴Biying Chen,⁴Marta Zurakowska,⁴Jamie D. Gilmour,^1,2Louise Alexander,^1,2Ian A. Crawford,³Katherine H. Joy
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13783]
¹Department of Earth and Planetary Science, Birkbeck College, University of London, Malet Street, London, WC1E 7HX UK
²The Centre for Planetary Sciences at UCL-Birkbeck, Gower Street, London, WC1E 6BT UK
³Department of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL UK
⁴Isotope Geosciences Unit, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF UK
Published by arrangement with John Wiley & Sons

We report the concentrations and isotope ratios of light noble gases (He, Ne, Ar) in 10 small basalt fragments derived from lunar regolith soils at the Apollo 12 landing site. We use cosmic ray exposure (CRE) and shielding condition histories to consider their geological context. We have devised a method of using cosmogenic Ne isotopes to partition the CRE history of each sample into two stages: a duration of “deep” burial (shielding of 5–500 g cm−2) and a duration of near-surface exposure (shielding of 0 g cm−2). Three samples show evidence of measurable exposure at the lunar surface (durations of between 6 ± 2 and 7 ± 2 Myr). The remaining seven samples show evidence of a surface residence duration of less than a few hundred thousand years prior to collection. One sample records a single-stage CRE age range of between 516 ± 36 and 1139 ± 121 Myr, within 0–5 g cm−2 of the lunar surface. This is consistent with derivation from ballistic sedimentation (i.e., local regolith reworking) during the Copernicus crater formation impact at ~800 Myr. The remaining samples show CRE age clusters around 124 ± 11 Myr and 188 ± 15 Myr. We infer that local impacts, including Surveyor crater (180–240 Ma) and Head crater (144 Ma), may have brought these samples to depths where the cosmic ray flux was intense enough to produce measurable cosmogenic Ne isotopes. More recent small impacts that formed unnamed craters may have exhumed these samples from their deep shielding conditions to the surface (i.e., ~0–5 g cm−2) prior to collection from the lunar surface during the Apollo 12 mission.

^1,2Yan Fan,¹Shijie Li,¹Shen Liu,³Hao Peng,⁴Guangming Song,⁵Thomas Smith
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13789]
¹State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an, 710069 China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
³Xi’an Astronautics Composite Materials Institute, Xian, 710025 China
⁴Beijing Institute of Spacecraft Environment Engineering, Beijing, 100094 China
⁵State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
Published by arrangement with John Wiley & Sons

In recent years, numerous meteorites have been collected in desert areas in northern and western China. We describe the environment of some deserts in this region, and the petrological and mineralogical characteristics of 49 of the recovered ordinary chondrites. They consist of 14 H chondrites, 33 L chondrites, and 2 LL chondrites. Of the 300 desert meteorites with approved names from deserts in China, there have been 287 ordinary chondrites, six iron meteorites, one CO3 chondrite, one diogenite, one ureilite, one brachinite, one eucrite, and one EL7 chondrite. Forty-two dense meteorite collection areas (DCAs) have been defined, mainly located in northern and western China. The meteorites collected are mainly from the Kumtag DCA, followed by the Alatage Mountain, Loulan Yizhi, Hami, and Lop Nur DCAs. After tentative pairing of the meteorites, we estimate that the ordinary chondrites account for 72% of the desert meteorites collected in China, with 63 H chondrites, 133 L chondrites, and 20 LL chondrites. This dominance of L chondrites contrasts with other deserts, which may result from the insufficient collection or bias in pairing of ordinary chondrites. The mass distribution of meteorites from different DCAs in China is consistent with that from DCAs in Africa. Based on the available information and the meteorite flux model proposed by previous studies, we suggest that the time over which meteorites have been accumulated in the southern Hami DCA might be >10 kyr. Therefore, the southern Hami region is currently the most suitable area for meteorite collection in China.

¹A.C.Martin,¹J.P.Emery,^1,2M.J.Loeffler
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114921]
¹Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, United States of America
²Center for Materials Interfaces in Research and Applications, Northern Arizona University, Flagstaff, AZ 86011, United States of America
Copyright Elsevier

Studies have long utilized laboratory derived spectra to understand the surface composition and other properties of planetary bodies. One variable that is believed to affect remotely acquired spectra in the mid-infrared (MIR; 5–35 μm) is the surface porosity of the airless body, yet there have been few laboratory studies to quantify this effect. Thus, here we report systematic laboratory experiments aimed at quantifying the effect that porosity has on the MIR spectra of silicate regoliths. To simulate the effects of regolith porosity, we mixed olivine powder with KBr powder of the same size range (< 20 μm, 20–45 μm, and 45–63 μm). Olivine was mixed with KBr from 0% – 90% with 10% intervals by weight. Finally, we measured spectra with a Fourier transform infrared (FTIR) spectrometer in the MIR. Our results indicate a transition from a primarily surface scattering regime to a primarily volume scattering regime with increasing regolith porosity. Evidence of the dominating regime transition includes: the primary Christiansen Feature at ~8.8 μm decreases in spectral contrast, and shifts slightly to longer wavelengths as regolith porosity increases, reststrahlen bands in the 10-μm do not shift significantly in wavelength but do decrease in spectral contrast, vibrational bands in the volume scattering regime (i.e., peaks in emissivity) increase in spectral contrast with increasing regolith porosity, and the spectral contrast of 10-μm plateau increases exponentially with increasing regolith porosity. The MIR spectral analysis of asteroids, such as Hektor, suggests a highly porous surface regolith (at least 81% void space) of fine-particulate silicates. These results demonstrate that some asteroids support highly porous regoliths whose spectra are not well-matched by standard (low porosity) laboratory spectra of powders. The spectra presented here enable analysis of both the porosity and mineralogy of olivine-rich, low porosity asteroid surfaces.

^1,2,3E.T.Dunham et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.002]
¹Arizona State University (ASU), Center for Meteorite Studies, Tempe, AZ, 85287-1404
²Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287-1404
³The University of California, Los Angeles (UCLA), Department of Earth, Planetary and Space Sciences, Los Angeles CA 90095-1567
Copyright Elsevier

Short-lived radionuclides (SLRs) once present in the solar nebula can be used as probes of the formation environment of our Solar System within the Milky Way Galaxy. The first-formed solids in the Solar System, calcium-, aluminum-rich inclusions (CAIs) in meteorites, record the one-time existence of SLRs such as 10Be and 26Al in the solar nebula. We measured the 10Be–10B isotope systematics in 29 CAIs from several CV3, CO3, CR2, and CH/CB chondrites and show that all except for a FUN CAI record a homogeneous initial 10Be/9Be with a single probability density peak at 10Be/9Be = 7.4 × 10–4. Integrating these data with those of previous studies, we find that most CAIs (81%) for which 10Be–10B isotope systematics have been determined, record a homogeneous initial 10Be/9Be ratio in the early Solar System with a weighted mean 10Be/9Be = (7.1 ± 0.2) × 10–4. This uniform distribution provides evidence that 10Be was predominantly formed in the parent molecular cloud and inherited by the solar nebula. Possible explanations for why unusual CAIs (FUNs, PLACs, those from CH/CBs, and those irradiated on the parent body) recorded a 10Be/9Be ratio outside of 7.1 × 10−4 include the following: 1) They incorporated a component of 10Be that was produced in the nebula by irradiation; 2) they formed after normal CAIs; and 3) they were processed (post-formation) in a way that affected their original 10Be signatures. Given the rarity of these examples, the overall uniformity of initial 10Be/9Be suggests that Solar System 10Be was predominantly inherited from the molecular cloud.

¹J. Aléon,^1,3D. Lévy,²A. Aléon-Toppani,¹H. Bureau,⁴H. Khodja,⁵F. Brisset
Nature Astronomy (in Press) Link to Article [DOI https://doi.org/10.1038/s41550-021-01595-7]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, CNRS UMR 7590, Museum National d’Histoire Naturelle, Paris, France
²Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS UMR 8617, Orsay, France
³Laboratoire des Fluides Complexes et leurs Réservoirs (LFCR), E2S UPPA – Université de Pau et des Pays de l’Adour, CNRS, Total, Pau, France
⁴Université Paris-Saclay, CEA, CNRS, NIMBE, LEEL, Gif sur Yvette, France
⁵Institut de Chimie Moléculaire et des Matériaux d’Orsay, Université Paris-Saclay, CNRS UMR 8182, Orsay, France

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¹Koichi Mimura,¹Riku Okada
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.01.030]
¹Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan
Copyright Elsevier

Shock experiments on an aqueous l-alanine solution were undertaken to examine the significance of cometary impacts in supplying prebiotic compounds to the early Earth. The shock pressures and temperatures ranged from 6.5 to 34.0 GPa and 516 to 963 K, respectively. Alanine in the shocked samples decreases in abundance and has higher d/l ratios as the shock temperature increases. The shocked sample at 963 K contained 33% of the starting alanine, which had a d/l value of 0.51. The shocked samples above 643 K all contained isomers of the alanine dimer Ala–Ala, including l-Ala–l-Ala, l-Ala–d-Ala, d-Ala–l-Ala, and d-Ala–d-Ala. A comparison of our study with previous studies indicates that water inhibits the decomposition of alanine and promotes racemization during shock compression. We calculated the shock temperatures at various impact velocities to determine the impact velocity at which alanine can survive when comets and meteorites impact the land or ocean at different impact angles. This impact velocity was much lower for comets than meteorites. The reduction in alanine decomposition caused by water is compensated for by the high shock temperature produced by the high porosity of comets. However, considering that comets are effectively decelerated by airburst and contain large amounts of organic materials, comets would be more important than meteorites in terms of delivering prebiotic compounds, including amino acid dimers with ll enantiomeric excesses, to the early Earth. Comets are likely to have played a key role in the biogeochemical evolution of the early Earth.