^1,2,3E.S.Steenstra,³J.Berndt,³A.Rohrbach,¹E.SBullock,²W.van Westrenen,³S.Klemme,¹M.J.Walter
Geochimica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.021]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington D.C, U.S.A
²Faculty of Science, Vrije Universiteit Amsterdam, the Netherlands
³Institute of Mineralogy, University of Münster, Germany
Copyright Elsevier

The abundances of highly siderophile elements (HSE) in planetary mantles and achondrites potentially provide important constraints on several aspects of planet formation, including the nature and composition of late accreted materials. Here, we experimentally and systematically assess the distribution of the HSE between silicate melts, sulfide and/or metal liquids at the highly to moderately reduced conditions thought to have characterized Earth accretion. The results show that the chalcophile behavior of all elements, except for Re, is strongly decreased at low FeO and/or high S concentrations in the silicate melt. There are considerable differences between how FeO and/or S contents of the silicate melt affect the D values of the various HSE, with the largest effects observed for Pd, Pt, Ir and Au. If liquid metal is Si-rich and S-poor, the siderophile behavior of the HSE mimics that in the presence of sulfide liquids, but with an offset due to differences in HSE activities in metal and sulfide liquids.

Using our new experimental data, we quantify the relative effects of O in sulfide and S in silicate melt on the sulfide liquid-silicate melt partitioning behavior of the HSE using a thermodynamic approach. The resulting expressions were used to model the distribution of the HSE in highly reduced and differentiated EH- and EL chondritic parent bodies and during differentiation of the aubrite parent body. Our results show that even with their strongly decreased chalcophile and siderophile behavior at highly reduced conditions, HSE abundances in the mantles of these parent bodies remain extremely low. However, if such bodies accreted to Earth, any residual metal present in the parent body mantle and subsequently retained in Earth’s mantle would dramatically affect HSE abundances and produce chondritic ratios, making it impossible to track the potential accretion of a large reduced impactor to the BSE using HSE abundance systematics. In terms of the aubrite parent body, our results confirm previous hypotheses related to the importance of (un)differentiated core forming metals in establishing the HSE contents of unbrecciated aubrites. Finally, our results confirm that sulfides are likely a minor source of HSE abundances in aubrites, particularly for Re, consistent with sample observations.

¹Jérôme Esvan,²Gilles Berger,³Sébastien Fabre,⁴Eric Bêche,¹Yannick Thébault,²Alain Pages,¹Cédric Charvillat
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.017]
¹CIRIMAT, CNRS-UPS-INPT, ENSIACET, 4 allée Emile Monso, 31030 Toulouse, France
²IRAP, CNRS, Observatoire Midi-Pyrénées, 14 av. Edouard Belin, 31400 Toulouse, France
³IRAP, Université Paul Sabatier, Observatoire Midi-Pyrénées, 14 av. Edouard Belin, 31400 Toulouse, France
⁴PROMES, PCM-ASI-CNRS, 7 rue du Four Solaire, 66120 Font-Romeu, France
Copyright Elsevier

Extreme conditions encountered in some geological contexts (deep serpentinization, interaction of Venus atmosphere with its basaltic surface, volcanic degassing) activate mechanisms and rates of silicate alteration that are poorly understood. In the present study, we investigate the mechanisms of mineral reactions in a natural geological system at high temperature, under conditions where the low solvation of cations by fluids likely promotes surface reactions such as surface diffusion and/or local recrystallization. We focus on vitreous glasses and olivine, reputed to be the most alterable phases in volcanic rocks, by reacting samples for one week in a Ni-based alloy experimental vessel. For the framework of our experimental study, we chose to apply the deep atmosphere conditions on Venus: 470°C and 90 bar of reconstituted Venus-like gas. We also tested the effect of water (Early Venus or wet volcanic degassing) by adding water vapor at up to 320 bar total pressure. The mineral reactions affecting the samples were identified by a set of spectroscopic surface analyses of the altered samples: Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-Ray Diffraction in grazing incidence mode, X-ray Photo electron Spectroscopy and Raman spectroscopy.

Samples of obsidian and tholeiitic glasses are found to be sensitive to a threshold water pressure, depending on glass composition, below which the reaction is limited to some elemental mobility in the glass (alkali enrichment, calcium loss) leading to a possibly more stable surface layer of tens to hundreds of microns. Above this threshold water pressure (ca. 50 bar H2O for the obsidian but >250 bar H2O for the tholeiitic glass), water promotes the depolymerization of the glass and the crystallization of stable minerals. This crystalline rim is less protective that the chemically modified layer.

Olivine samples react differently depending on whether the olivine is isolated or included in a basaltic rock. In the latter case only, iron coatings are formed, which are identified as hematite, suggesting that this phase is not fed by olivine itself but rather by surface diffusion from neighboring Fe-rich phases. This supports the conclusions from experimental studies and orbital observations on the short-term visibility of unaltered olivine in Venus lava flows: such a coating is enhanced when Fe-bearing minerals are in the proximity of olivine. Under high water vapor pressure, Fe-bearing talc (and not serpentine) forms by a likely topotactic reaction that also incorporates silica from the gas. This talc layer may form a protective layer, implying that serpentinization of ultramafic rocks at high temperature may not be as prevalent as one might think in a gas-dominated system like the Early Venus surface.

^1,2Camilla Cioria,^1,2Giuseppe Mitri
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115234]
¹International Research School of Planetary Sciences, Pescara, Italy
²Dipartimento di Ingegneria e Geologia, Università d’Annunzio, Pescara, Italy
Copyright Elsevier

Triton, the largest satellite of Neptune, is one of the most fascinating icy moons in the outer Solar System, with an origin that likely extends to the Kuiper Belt. Like other icy satellites, the mineralogical composition of Triton’s deep interior is a function of its evolutionary path. In this work, we use the open- access Perple_X software to model the evolutionary paths, anhydrous and hydrous, describing three different mineralogical models to investigate the possible mineral composition forming the rocky fraction of Triton’s deep interior. We modelled the phase assemblages adopting three carbonaceous chondrites (Orgueil, Murchison, Allende) as precursor material of the proto-Triton. We found that Triton’s deep interior could have evolved during its history into three possible mineral assemblages: an anhydrous deep interior rich in olivine and pyroxenes, a hydrous deep interior rich in hydrated silicates, and a dehydrated deep interior rich in hydrated silicates (amphiboles and chlorite), olivine and pyroxenes. We show that future measurement of the gravity field of Triton can be used to determine the present mineral assemblages of its deep interior.

¹A.-M.Seydoux-Guillaume,²T.de Resseguier,³G.Montagnac,⁴S.Reynaud,⁵H.Leroux,³B.Reynard,⁶A.J.Cavosie
Earth and Planetary Science Letters 595, 117727 Link to Article [https://doi.org/10.1016/j.epsl.2022.117727]

¹Univ Lyon, UJM, UCBL, ENSL, CNRS, LGL-TPE, F-42023 Saint Etienne, France
²PPRIME, CNRS-ENSMA-Université de Poitiers, 1 avenue Clément Ader, 86961 Futuroscope, France
³Univ Lyon, ENSL, UCBL, UJM, CNRS, LGL-TPE, F-69007 Lyon, France
⁴Université de Lyon, UJM-Saint-Etienne, CNRS, Institut d’Optique Graduate School, Laboratoire Hubert Curien UMR 5516, F-42023 Saint-Etienne, France
⁵Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France
⁶The Space Science and Technology Centre (SSTC) and the Institute for Geoscience Research (TIGeR), School of Earth and Planetary Science, Curtin University, Perth, WA 6102, Australia
Copyright Elsevier

Impact-related damage in minerals and rocks provides key evidence to identify impact structures, and deformation of U-Th-minerals in target rocks, such as monazite, makes possible precise dating and determination of pressure-temperature conditions for impact events. Here a laser-driven shock experiment using a high-energy laser pulse of ns-order duration was carried out on a natural monazite crystal to compare experimentally produced shock-deformation microstructures with those observed in naturally shocked monazite. Deformation microstructures from regions that may have experienced up to ∼50 GPa and 1000 °C were characterized using Raman spectroscopy and transmission electron microscopy. Experimental results were compared with nanoscale observations of deformation microstructures found in naturally shocked monazite from the Vredefort impact structure (South Africa). Raman-band broadening observed between unshocked and shocked monazite, responsible for a variation of ∼3 cm−1 in the FWHM, is interpreted to result from the competition between shock-induced distortion of the lattice, and post-shock annealing. At nanoscale, three main plastic deformation structures were found in both naturally and experimentally shocked monazite: deformation twins, mosaïcism, and deformation bands. The element Ca is enriched along host-twin boundaries, which further confirms that the laser shock loading experiment produced both comparable styles of crystal-plastic deformation, and also localized element mobility, as that found in natural shock-deformed monazite. Deformation twins form in the experiment were only along the (001) plane, an orientation which is not considered diagnostic of shock deformation. However, both mosaïcism and deformation, expressed in SAED patterns as streaking of spots, and the presence of extra spots (more or less pronounced), are interpreted as unambiguous nano-scale signatures of shock metamorphism in monazite. Experimentally calibrated deformation features, such as those documented here at TEM-scale, provide new tools for identifying evidence of shock deformation in natural samples.

¹Oliver Christ,¹Anna Barbaro,²Frank E. Brenker,¹Paolo Nimis,¹Davide Novella,³M. Chiara Domeneghetti,^1,2Fabrizio Nestola
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13907]
¹Department of Geosciences, University of Padova, Via Gradenigo 6, 35131 Padova, Italy
²Geoscience Institute, Goethe-University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany
³Department of Earth and Environmental Sciences, University of Pavia, Via A. Ferrata 1, I-27100 Pavia, Italy
Published by arrangement with John Wiley & Sons

Carbon aggregates from two differently shocked ureilites were analyzed to gain insight into the shock transformation of graphite to diamond in ureilites, which happened when the ureilite parent body (UPB) was most likely destroyed by massive impact events. We present data for carbon aggregates from the highly shocked (U-S6) Northwest Africa (NWA) 6871 and the medium shocked (U-S3) NWA 3140. Both samples contain abundant carbon aggregates which were analyzed by X-ray diffraction and micro-Raman spectroscopy revealing the presence of close associations of (compressed) nanographite, micro- and nanodiamond, as well as Fe-rich phases. Graphite and diamond in NWA 6871 show shock indicators that are absent in NWA 3140. Based on Raman geothermometry on graphite, we calculated mean temperatures of 1368 ± 120 °C and 1370 ± 120 °C for NWA 3140 and NWA 6871, respectively. For comparison, a geothermometer based on the partitioning of Cr between olivine and low-Ca pyroxene was applied on NWA 3140, which yielded a temperature of only 1215 ± 16 °C. The graphite-based temperatures are the highest reported for graphite in ureilites so far and exceed calculated magmatic temperatures for ureilites from silicate- and chromite-based geothermometers. Graphite temperatures fall into the temperature field of catalytic diamond synthesis, which supports the hypothesis of direct transformation from graphite to diamond upon shock. Although the temperatures estimated seem to be independent of the shock degree, they can be ascribed to the shock event that destroyed the UPB.

¹Addi Bischoff,¹Markus Patzek,^2,3Stefan T. M. Peters,^4,5Jean-Alix Barrat,²Tommaso Di Rocco,²Andreas Pack,¹Samuel Ebert,¹Christian A. Jansen,⁶Kryspin Kmieciak
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13905]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, German
²Universität Göttingen, Geowissenschaftliches Zentrum, Goldschmidtstr. 1, D-37077 Göttingen, Germany
³Museum der Natur Hamburg – Mineralogie, LIB, Grindelallee 48, D-20146 Hamburg, Germany
⁴University of Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzané, France
⁵Institut Universitaire de France, Paris, 75005 France
⁶Olsza 2, 63-100 Śrem, Kraków, Poland
Published by arrangement with John Wiley & Sons

On July 15, 2021, a huge fireball was visible over Poland. After the possible strewn field was calculated, the first and so far only sample, with a mass of 350 g, was discovered 18 days after the fireball event. The Antonin meteorite was found August 3, 2021, on the edge of a forest close to a dirt road near Helenow, a small suburb of the city of Mikstat. The rock is an ordinary chondrite breccia and consists of equilibrated and recrystallized lithologies. The boundaries between different fragments are difficult to detect, and the lithologies are of petrologic type 5 and type 4. The rock is moderately shocked (S4) and contains local impact melt areas and thin shock veins. The low-Ca pyroxene and olivine are equilibrated (Fs20.6 and Fa24.0, respectively), typical of L chondrites. The L chondrite classification is also supported by O isotope data and the results of bulk chemical analysis. The Ti isotope characteristics confirm that Antonin is related to the noncarbonaceous (NC) meteorites. One of the studied thin sections shows an unusual metal–chondrule assemblage, perhaps indicating that the metal in the chondrite is heterogeneously distributed, which is, however, not clearly visible in the element abundances.

¹Emmanuel Jacquet
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13896]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum national d’Histoire naturelle, Sorbonne Université, CNRS, CP52, 57 rue Cuvier, 75005 Paris, France
Published by arrangement with John Wiley & Sons

The current meteorite taxonomy, a result of two centuries of meteorite research and tradition, entangles textural and genetic terms in a less than consistent fashion, with some taxa (like “shergottites”) representing varied lithologies from a single putative parent body while others (like “pallasites”) subsume texturally similar objects of multifarious solar system origins. The familiar concept of “group” as representative of one primary parent body is also difficult to define empirically. It is proposed that the classification becomes explicitly binominal throughout the meteorite spectrum, with classes referring to petrographically defined primary rock types, whereas groups retain a genetic meaning, but no longer tied to any assumption on the number of represented parent bodies. The classification of a meteorite would thus involve both a class and a group, in a two-dimensional fashion analogous to the way Van Schmus and Wood decoupled primary and secondary properties in chondrites. Since groups would not substantially differ, at first, from those in current use de facto, the taxonomic treatment of “normal” meteorites, whose class would bring no new information, would hardly change. Yet classes combined with high- or low-level groups would provide a standardized grid to characterize petrographically and/or isotopically unusual or anomalous meteorites—which make up the majority of represented meteorite parent bodies—for example, in relation to the carbonaceous/noncarbonaceous dichotomy. In the longer term, the mergers of genetically related groups, a more systematic treatment of lithology mixtures, and the chondrite/achondrite transition can further simplify the nomenclature.

¹Sergey E. Kichanov,^1,2Bekhzodjon A. Abdurakhimov,¹Ivan Yu Zel,¹Andrei K. Kirillov,¹Denis P. Kozlenko,³Irina K. Lapina,³Yulii L. Mentsin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13903]
¹FLNP, Joint Institute for Nuclear Research, 141980 Dubna, Russia
²Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan, 100214 Tashkent, Uzbekistan
³Museum of the History of Astronomy, Sternberg Astronomical Institute, Lomonosov Moscow State University, 119992 Moscow, Russia
Published by arrangement with John Wiley & Sons

We present the results of neutron methods, specifically neutron diffraction and neutron tomography, in studying the structural organization of a Kunya-Urgench chondrite fragment. The major phases of the meteorite fragment and variation of the phase content across the studied volume were revealed using neutron diffraction. The 3-D model of the spatial distribution of metal and silicate phases inside the meteorite volume was obtained using neutron tomography. The distributions of volumes, average sizes, and shape-related parameters of kamacite and silicate phases were analyzed. Shape preferred orientations of the kamacite particles were observed and the origins of shape fabric of these particles were discussed.

^1,2Brendt C. Hyde,¹Desmond E. Moser,²Kimberly T. Tait,³James R. Darling,⁴Qing-Zhu Yin,⁴Matthew E. Sanborn,^1,2Neil R. Banerjee,^1,2Arshad Ali,¹Iffat Jabeen,³Hugo Moreira
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13897]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7 Canada
²Department of Natural History, Royal Ontario Museum, Toronto, Ontario, M5S 2C6 Canada
³School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, PO13QL UK
⁴Department of Earth and Planetary Sciences, University of California Davis, One Shields Avenue, Davis, California, 95616 USA
Published by arrangement with John Wiley & Sons

Detailed textural and geochemical analyses of the carbonaceous achondrites Northwest Africa (NWA) 7680 and NWA 6962 support a rapid progression of thermal events, by similar processes, on the same parent body. The achondrites have olivine compositions of Fa44.8 and Fa47.4 for NWA 7680 and NWA 6962, respectively. Replicate oxygen isotope analyses of grains and bulk powders from NWA 7680 yielded average Δ17O values of −1.04 ± 0.03‰ and −1.00 ± 0.05‰, respectively, which is identical to that reported for NWA 6962. The whole rock ɛ54Cr compositions are also equivalent for NWA 7680 and NWA 6962 (1.36 ± 0.05 and 1.30 ± 0.05, respectively). Both meteorites are plagioclase-rich, and NWA 7680 is also Fe-metal-rich, suggesting they both formed via differentiation processes that resulted in the pooling of partial melt products. Major element geochemical trends show that both rocks could be formed through the melting of chondritic material on a CR chondrite-like parent body. This is consistent with oxygen isotope and chromium isotope compositions. Intrusion of a late-stage melt is evident in both meteorites and the crystallization products include silica-rich, alkali-deficient nepheline. The late-stage liquid has partially melted and mixed with primary plagioclase in NWA 6962. In contrast, the late-stage liquid was often restricted to grain boundaries in NWA 7680, leaving some of the primary plagioclase crystals intact. In situ dating of NWA 7680 phosphate minerals (merrillite and fluorapatite) reveals that it has not experienced long duration thermal metamorphism, or impact-related Pb loss and age resetting since 4578 ± 17 Ma (207Pb/206Pb age ± 2σ, within error of solar system age). Phosphates associated with the late-stage melt in NWA 6962 yield a 207Pb/206Pb age of 4556.6 ± 8.0 Ma (2σ) within 2σ of the NWA 7680 age. These early dates indicate that the observed chromium isotope signatures in these meteorites were not introduced by a later high-temperature event, such as late impact accretion processes. These data are consistent with a rapid separation of inner and outer solar system chemical reservoirs, planetesimal melting, differentiation, and cooling, all within several million years of calcium-aluminum-rich inclusion formation.

^1,2John Carter,³Lucie Riu,¹François Poulet,¹Jean-Pierre Bibring,¹Yves Langevin,¹Brigitte Gondet
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115164]
¹Institut d’Astrophysique Spatiale (IAS), CNRS/Paris-Saclay University, France
²Laboratoire d’Astrophysique de Marseille (LAM), CNRS/Aix-Marseille University, France
³ESA-ESAC, Madrid, Spain
Copyright Elsevier

We describe the completion of the MOCAAS project providing a global repository of secondary minerals formed through interaction with water on Mars. This work is based on the analysis of orbital imaging spectroscopy data from the OMEGA/Mars Express and CRISM/MRO near-infrared instruments. A database and a set of high-resolution global maps (200 m/pix) are produced which provide a large collection of these “aqueous” secondary mineral deposits, most of which were not previously reported. Several aqueous mineral classes are discriminated including hydrated silicates, hydrated silica, sulfate and carbonate salts. A preliminary statistical analysis on the database of aqueous mineral deposits is carried out, revealing significantly more widespread and diverse aqueous alteration on Noachian and Hesperian Mars than previously seen. Higher resolution local scale studies are also carried out over current and prospective rover landing sites on Mars, providing enhanced sensitivity to mineral detection and reachable science targets. Collectively, the data presented here at all scales is expected to foster synergy between orbital and landed missions, particularly for future missions and to pinpoint prospective resources for human exploration.