¹Jens Barosch,¹Larry R. Nittler,¹Jianhua Wang,²Elena Dobrică,³Adrian J. Brearley,⁴Dominik C.Hezel,¹Conel M. O’D. Alexander
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.027]
¹Earth and Planets Laboratory, Carnegie Institution of Washington, 5241 Broad Branch Rd. NW, Washington DC 20015, USA
²Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, 1680 East-West Road, Honolulu 96822, USA
³Department of Earth and Planetary Sciences, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA
⁴Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, 60438, Frankfurt am Main, Germany
Copyright Elsevier

Presolar grains are trace components in chondrite matrices. Their abundances and compositions have been systematically studied in carbonaceous chondrites but rarely in situ in other major chondrite classes. We have conducted a NanoSIMS isotopic search for presolar grains with O- and C-anomalous isotopic compositions in the matrices of the unequilibrated ordinary chondrites Semarkona (LL3.00), Meteorite Hills 00526 (L/LL3.05), and Northwest Africa 8276 (L3.00). The matrices of even the most primitive ordinary chondrites have been aqueously altered and/or thermally metamorphosed, destroying their presolar grain populations to varying extents. In addition to randomly placed isotope maps, we specifically targeted recently reported, relatively pristine Semarkona matrix areas to better explore the original inventory of presolar grains in this meteorite. In all samples, we found a total of 122 O-anomalous grains (silicates + oxides), 79 SiC grains, and 22 C-anomalous carbonaceous grains (organics, graphites). Average matrix-normalized abundances with 1σ uncertainties are ppm O-anomalous grains, ppm SiC grains and ppm carbonaceous grains in Semarkona, ppm (O-anom.), ppm (SiC) and ppm (carb.) in MET 00526 and ppm (O-anom.), ppm (SiC) and ppm (carb.) in NWA 8276. In relatively pristine ordinary chondrites and in primitive carbonaceous and C-ungrouped chondrites, the O and C isotopic composition of presolar grains and their matrix-normalized abundances are similar, despite the likely differences in chondrite-formation time and nebular location. These results suggest a relatively homogenous distribution of presolar dust across major chondrite-forming reservoirs in the solar nebula. Secondary asteroidal processes are mainly responsible for differences in presolar grain abundances between and within chondrites, highlighting the need to identify and target the most pristine chondrite matrices for such studies.

¹Samuel Ebert,²Kazuhide Nagashima,¹Addi Bischoff,³Jasper Berndt,²Alexander N.Krot
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.026]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany
²School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, USA
³Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Germany
Copyright Elsevier

Understanding the genetic relationship between different chondritic components will help to decipher their origin and dynamical evolution within the protoplanetary disk. Here, we obtain insight into these processes by acquiring O-isotope data from 17 Al-rich chondrules from unequilibrated ordinary chondrites (OCs, petrologic type ≤3.2) and four Al-rich chondrules from the CO3.1 carbonaceous chondrite Dar al Gani (DaG) 083. These particular kinds of chondrules are of special interest, as it is suggested that their precursors may have contained refractory material related to Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs).

The four investigated Al-rich chondrules from the CO3.1 chondrite Dar al Gani 083 consist of olivine, low-Ca pyroxene, Ca pyroxene, and spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Two chondrules have a homogeneous O-isotopic composition and two are heterogeneous in composition. One chondrule contains relict spinel grains with a Δ17O value of −24.3±1.3‰, indicative of 16O-rich precursor refractory material, similar to constituents of CAIs and AOAs. The presence of CAI-like precursors for the Al-rich chondrules from CO chondrites is consistent with their previously reported presence of 50Ti excesses (Ebert et al., 2018).

The Al-rich chondrules in the ordinary chondrites studied consist of olivine, low-Ca pyroxene, Ca pyroxene, and, occasionally, spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Hibonite is present in one Al-rich chondrule. The vast majority of these chondrules have heterogeneous O-isotopic compositions: Chondrule glasses are 16O-depleted compared to chondrule phenocrysts; the Δ17O values of the former approach those of aqueously formed fayalite and magnetite grains in type 3 OCs, ∼ +5‰. We infer that the chondrule glasses experienced O-isotope exchange with an aqueous fluid on the OC parent asteroids.

Chondrule phenocrysts, like spinel, olivine, low-Ca pyroxene, and Ca pyroxene, were not affected by this isotope exchange and preserved their initial O-isotope compositions. The phenocrysts within individual chondrules have similar Δ17O, whereas the inter-chondrule Δ17O values range from −4.5 to +1.4‰, i.e., they are in general 16O enriched relative to the majority of ferromagnesian type I and type II porphyritic chondrules in OCs having Δ17O of ∼ +1‰. Because no relict grains were identified in the Al-rich chondrules from ordinary chondrites, the original O-isotopic composition of the refractory precursor material remains unknown.

Additional detailed Na measurements within olivine grains show no major changes in the Na content of the chondrule melt during their crystallization. This implies either that the Na was part of the precursor material or that the Na was enriched in the chondrule melt/glass after crystallization of the olivines.

¹Toshihiro Tada,^1,2,3Ryuji Tada,⁴Paul A. Carling,⁵Wickanet Songtham,⁵Praphas Chansom,¹Toshihiro Kogure,¹Yu Chang,¹Eiichi Tajika
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13908]
¹Institute for Geo-Cosmology, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba, 275-0016 Japan
²Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo, 113-0033 Japan
³Research Center for Earth System Science, Yunnan University, Chenggong District, Kunming, 650500 People’s Republic of China
⁴Geography and Environmental Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ UK
⁵Northeastern Research Institute of Petrified Wood & Mineral Resources, Nakhon Ratchasima Rajabhat University, Baan Kroke Duen Ha, Suranaree Sub-district, Muang Nakhon Ratchasima District, Nakhon Ratchasima, 30000 Thailand
Published by arrangement with John Wiley & Sons

The Australasian Tektite Event, approximately 0.8 Ma, is the youngest record of a large impact event on Earth. Although it is estimated that it occurred somewhere in Indochina based on the distribution of tektites, the crater has never been located. Here, we report the discovery and occurrence of shocked quartz with planar deformation features (PDFs) in the Quaternary depositional sequence at Huai Om in northeastern Thailand. Measurements of the orientation of lamellae using a universal stage microscope as well as observation using scanning electron microscopy and transmission electron microscopy were conducted to confirm the presence of PDFs. Together with the occurrence of in situ layered tektite fragments, we identify the depositional sequence as the ejecta deposit formed by the Australasian Tektite Event. We further describe the detailed lithostratigraphy of the ejecta deposit, which will allow the tracing of its distribution and lateral changes in its thickness, grain size, and grain composition. Further investigation of the lateral distribution of the ejecta deposit would provide information about the location, magnitude, and target rocks of the Australasian Tektite Event.

¹Allan H. Treiman,²Jacob M. LaManna,²Daniel S. Hussey,³Isabella deClue,⁴Lawrence M. Anovitz
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13904]
¹Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, Texas, 77058 USA
²Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899 USA
³University of Chicago, Chicago, Illinois, 60637 USA
⁴Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37830 USA
Published by arrangement with John Wiley & Sons

The presence and distribution of hydrogen-bearing materials in meteorites are important constraints on processes in the early solar system, and the delivery of volatile constituents to growing planets. Here, we show that coordinated neutron and X-ray computed tomography, NXCT, can reveal the presence and distributions of hydrogen-bearing materials in meteorites, and thus help constrain the presence and actions of water in the early solar system. NXCT is nearly nondestructive of meteorite samples. Neutron fluence in NXCT is approximately seven orders of magnitude less than in typical instrumental neutron activation analysis, and so produces little residual radioactivity and currently undetectable changes in isotope ratios. Heating during NXCT is minimal, but NXCT will overprint the record of cosmic ray exposure held in natural thermoluminescence. Two meteorites were examined. EET 87503 is a howardite, a regolith breccia inferred to be from the asteroid 4 Vesta, and contains fragments of eucrite basalt, diogenite pyroxenite, and H-rich carbonaceous chondrites. With NXCT, the chondrite fragments within the meteorite piece can be clearly located and characterized, in preparation for possible extraction and detailed analyses. Graves Nunataks (GRA) 06100 is a CR2 chondrite meteorite that contains abundant iron metal and H-bearing silicates from aqueous alteration. In NXCT, H-bearing altered material is clearly distinguished from metal, and its distribution in three dimensions is revealed as a constraint on the processes of alteration.

^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.