¹Marine Ciocco,¹Mathieu Roskosz,¹Béatrice Doisneau,¹Olivier Beyssac,¹Smail Mostefaoui,¹Laurent Remusat,²Hugues Leroux,¹Matthieu Gounelle
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13793]
¹Institut de Minéralogie, de Physique des matériaux et de Cosmochimie (IMPMC), CNRS – UMR 7590, Sorbonne Université, MNHN, 75005 Paris, France
²Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France
Published by arrangement with John Wiley & Sons

The dynamics of collisional events have been studied for three highly shocked L chondrites (Tenham, Sixiangkou, and Acfer 040). Crystal growth rates of high-pressure polymorphs of olivines and pyroxenes and diffusion-driven redistribution of Mn, Ca, Fe, and Na associated with these polymorphic transitions were studied independently. These two approaches were then applied on the same samples, and for meteorites that underwent different collisional histories. The relevance of the use of pyroxene polymorphs (e.g., akimotoite) is demonstrated. Combined analysis of the exact same ringwoodite and akimotoite crystals by scanning transmission electron microscopy (STEM) and NanoSIMS demonstrate that while STEM has a better lateral resolution, the 40 nm maximum resolution of the NanoSIMS is sufficient to distinguish and analyze diffusion profiles. With STEM chemical and structural information concerning the nucleation mechanisms of ringwoodite and akimotoite, the concentration profiles derived from NanoSIMS images were used to derive the shock pulse duration and impactor size for these three meteorites. The two approaches (crystal growth kinetics and elemental diffusion) provide comparable durations assuming that diffusion coefficients are carefully selected. We obtain shock time scales of 1, 7, and 4 s for Tenham, Sixiangkou, and Acfer 040, respectively. Corresponding impactor sizes are also calculated, and the results point toward either (i) an early separation of the L chondrites from the parent body, and secondary impacts resulting in the observed meteorites or (ii) the meteorites all originate from different depths in the parent body.

¹A. Nathues,¹M. Hoffmann,²N. Schmedemann,¹R. Sarkar,³G. Thangjam,¹K. Mengel,¹J. Hernandez,²H. Hiesinger,²J. H. Pasckert
Nature Communications 13, 927 Link to Article [DOIhttps://doi.org/10.1038/s41467-022-28570-8]
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077, Goettingen, Germany
²Institut für Planetologie, WWU Münster, Münster, Germany
³School of Earth and Planetary Sciences, National Institute of Science Education and Research, NISER, HBNI, Bhubaneswar, India

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¹E.Bruschini,¹C.Carli,^1,2A.C.Buellet,³M.Vincendon,¹F.Capaccioni,¹M.Ferrari,^4,5F.Vetere,⁶A.Secchiari,⁷D.Perugini,⁶A.Montanini
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114950]
¹Institute for Space Astrophysics and Planetology – INAF, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
²AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, F-91191 Gif-sur-Yvette, France
³Institut d’Astrophysique Spatiale, Bâtiment 121, Université Paris-Saclay, CNRS, Orsay, France,
⁴Institute of Mineralogy, Leibniz Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany
⁵Dipartimento di Ingegneria & Geologia (InGeO), Università G. D’Annunzio di Chieti-Pescara, Via dei Vestini 31, 66100 Chieti, Italy
⁶Dept. of Chemistry, Life Sciences and Environmental Sustainability University of Parma, Parco Area delle Scienze 157/a, 43124 Parma, Italy
⁷University of Perugia, Department of Physics and Geology Piazza Università, 06100 Perugia, Italy
Copyright Elsevier

We report the VNIR (350–2500 nm) reflectance spectra of a suite of silicic samples mixed with graphite. We used three end-member materials with different chemical composition in order to have a comprehensive understanding of the effect of opaque minerals on reflectance spectra of silicic rocks. To decouple the effect of granulometry and graphite content on reflectance properties, we first measured the reflectance spectra for each end member at different grainsizes (between ⁓20 to 250 μm). Three selected grainsizes for each end-member were then mixed with graphite in the graphite/end-member weight ratio 1 to 5%. For each spectrum we evaluated the main band parameters (position, area, depth). Moreover, we also proposed and discussed the use of an additional parameter, the band centroid. Our results confirm that graphite mixed with silicate materials reduces albedo and decreases the spectral slopes and the spectral contrast of the mixtures. We discussed the subtle interplay between grain size, graphite content and chemical composition of the mixtures. We showed how graphite decreases the spectral slopes of the graphite-silicate mixtures proportionally to iron content (albedo) of the mixtures: low iron (bright) materials are more sensitive to spectral slope variation (decrease) as a function of graphite content. Finally we show how spectral slope influences the measured band parameters.

¹Christian Koeberl et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.021]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
Copyright Elsevier

The presence of tektite-like glasses from a geographically restricted area in Belize (Central America) has been known for several decades. We comprehensively studied 18 such Belize glasses by a variety of petrographic and geochemical methods, including major and trace element analysis, radiogenic isotopic composition (Rb-Sr, Sm-Nd, and Re-Os), water content, oxidation state, and cosmogenic radionuclides. The aims were to determine their compositional variation, their mode of formation and possible source rocks, and their relation to known tektites, and to search for evidence of an extraterrestrial component.

In terms of petrography, the samples are similar to tektites from the four “classical” strewn fields, with the presence of lechatelierites, schlieren, and vesicles; these are also widely accepted indicators of an impact origin. No close similarities to volcanic glasses are evident. Water contents are very low, and iron oxidation states are mostly reduced, in both cases similar to observations for other tektites. The geochemical and isotopic data presented, such as Cr, Co and Ni elemental abundances and interelement ratios, as well as trace element patterns are typical for local and regional volcanics from the active Central American Arc. Particular similarities to material comparable to volcanic rocks from Honduras or Guatemala are noted. This is confirmed by Sr-Nd isotope signatures of the Belize glasses, showing close similarities to Central American volcanics in general, and Honduran and Guatemalan volcanic, in particular. Osmium concentrations and 187Os/188Os ratios are comparable to arc volcanics from world-wide locations, but – in a few of the samples – elevated Ir concentrations, near-chondritic Pt/Ir and 187Os/188Os ratios can also be interpreted with the admixture of a minor meteoritic component to some of the Belize samples. 10Be concentrations are consistent with values typical of both, young or deeply buried soils and with values for Central American volcanics, which carry subducted 10Be.

Geochemical data clearly indicate a source different from that of the Australasian tektites. Both isotope data sets for the Belize glasses indicate a close relationship to local arc lavas, especially those from Guatemala and Honduras, suggesting that the glasses were not deposited very far from their source. The main evidence that the Belize glasses are of impact origin are their petrographic characteristics and low water content. The evidence from 10Be is consistent with, but does not require, a model of formation for the Belize glasses by an impact on loosely consolidated surface sediments exposed to rain. A probable meteoritic component is low and heterogeneously distributed.

¹Adnan Ahmad,¹Raj Patel,¹Bhaswati Deka,²Rohit Nagori,²A.S.Arya,¹Archana M.Nair
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114953]
¹Department of Civil Engineering, Indian Institute of Technology Guwahati, Assam, India
²Space Application Centre, Indian Space Research Organization, Ahmedabad, India
Copyright Elsevier

Identification of phyllosilicates on Mars suggests the existence of an aqueous environment, indicating an active period in its evolutionary history. This study analysed the surface mineralogy of caldera and flank regions of Tharsis Montes using remote spectral analysis. Though a thick layer of dust obscures the surface of Tharsis volcanic province, relatively lesser dust regions provide a unique window for exploration. The reflectance data obtained from CRISM onboard Mars Reconnaissance Orbiter in the visible-infrared region is used for the mineralogical study. Spectral parameter indices were used to identify the distribution of minerals over the caldera and flank regions of Tharsis Montes. The spectral characterisation indicates the well-distributed presence of mafic minerals such as olivine with low-calcium pyroxene and plagioclase with the sparse presence of high-calcium pyroxene in the region. The dusty region, typically with a high TES DCI index and low thermal inertia values in the Tharsis Montes, shows a high concentration of olivine. Few regions identified as comparatively dust-free at the caldera and flank show the presence of secondary mafic minerals like Fesingle bondMg bearing phyllosilicates. Our spectral analysis using nonlinear mixing models with the MICA spectral library indicates the occurrence of absorption features characteristic of hydrated minerals. The occurrence of the secondary mafic minerals, especially the phyllosilicates on Tharsis Montes suggest active weathering or hydrothermal alteration from episodic volcanic activity over time. Many factors on the Martian surface obstruct clean and noise-free data acquisition, pointing to the necessity of validating interpretations using multiple data sets.

¹Sheng Shang,^1,2Hejiu Hui,²Yueheng Yang,¹Tianyu Chen
Earth and Planetary Science Letters 581, 117413 Link to Article [https://doi.org/10.1016/j.epsl.2022.117413]
¹State Key Laboratory for Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
²CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
³State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

The observations of Martian orbiters and rovers have suggested that there were fluids on the surface of early Mars. However, the geochemical properties of those fluids are unclear. The Martian regolith breccia meteorites (MRB), the source materials of which are thought to have formed at 4.4 Ga, may have recorded interactions with fluids on Mars. Here, we have analyzed the in situ Sm-Nd isotopic compositions and trace element contents of apatite in MRB and have obtained a Sm-Nd isochron age of 1490±480 Ma. This young age indicates that the MRB apatites were altered by fluids and have exchanged trace elements with fluids. The very negative initial Nd, combined with the previously reported positive δD and Cl in the MRB apatites, indicate that Martian fluids originated from a geochemically enriched reservoir in the crust. The large ranges of rare earth element abundance (ΣREE) and of the chondrite normalized ratio of La and Yb [(La/Yb)N] indicate the chemical complexity of the fluids that interacted with the apatites in the MRB. The apatite REE compositions were used to further determine the pH values of Martian fluids equilibrated with the MRB apatites, which varied from ∼3 to ∼8. The apatite X-site Cl contents indicate that the Cl contents in Martian fluids in equilibrium with the MRB apatites at 400 °C and 1 bar could be up to 1857 ppm, within the range of terrestrial hydrothermal fluids. Combined with previously reported geochemical data from Martian meteorites, our study suggests that fluids may have been present throughout the early geological history of Mars.

¹Lars E. Borg,¹Gregory A. Brennecka,^1,2Thomas S. Kruijer
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.2115726119]
¹Nuclear and Chemical Science Division, Lawrence Livermore National Laboratory, Livermore, CA 94550;
²Department of Solar System, Impacts & Meteorites, Museum fur Naturkunde, Berlin 10115, Germany

The origin of volatile species such as water in the Earth–Moon system is a subject of intense debate but is obfuscated by the potential for volatile loss during the Giant Impact that resulted in the formation of these bodies. One way to address these topics and place constraints on the temporal evolution of volatile components in planetary bodies is by using the observed decay of ⁸⁷Rb to ⁸⁷Sr because Rb is a moderately volatile element, whereas Sr is much more refractory. Here, we show that lunar highland rocks that crystallized ∼4.35 billion years ago exhibit very limited ingrowth of ⁸⁷Sr, indicating that prior to the Moon-forming impact, the impactor commonly referred to as “Theia” and the proto-Earth both must have already been strongly depleted in volatile elements relative to primitive meteorites. These results imply that 1) the volatile element depletion of the Moon did not arise from the Giant Impact, 2) volatile element distributions on the Moon and Earth were principally inherited from their precursors, 3) both Theia and the proto-Earth probably formed in the inner solar system, and 4) the Giant Impact occurred relatively late in solar system history.

¹Rajkrishna Dutta et al. (>10)
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.2114424119]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015
²Department of Geosciences, Princeton University, Princeton, NJ 08544

Mg₂GeO₄ is important as an analog for the ultrahigh-pressure behavior of Mg₂SiO₄, a major component of planetary interiors. In this study, we have investigated magnesium germanate to 275 GPa and over 2,000 K using a laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction and density functional theory (DFT) computations. The experimental results are consistent with the formation of a phase with disordered Mg and Ge, in which germanium adopts eightfold coordination with oxygen: the cubic, Th₃P₄-type structure. DFT computations suggest partial Mg-Ge order, resulting in a tetragonal I4¯2d structure indistinguishable from I4¯3d Th₃P₄ in our experiments. If applicable to silicates, the formation of this highly coordinated and intrinsically disordered phase may have important implications for the interior mineralogy of large, rocky extrasolar planets.

¹Arianna E. Gleason et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13785]
¹SLAC National Accelerator Laboratory, Menlo Park, California, 94025 USA
Published by arrangement with John Wiley & Sons

Meteor impacts can induce unique pressure-dependent structural changes in minerals due to the propagation of shock waves. Plagioclase—ubiquitous throughout the Earth’s crust, extraterrestrial bodies, and meteorites—is commonly used for reconstructing the impact history and conditions of the parent bodies. However, there have been unresolved inconsistencies in the interpretation of shock transformations across previous studies: The pressure at which amorphization begins and the process by which it occurs is the subject of ongoing debate. Here, we utilize time-resolved in situ X-ray diffraction (XRD) to probe the phase transformation pathway of plagioclase during shock compression at a sub-nanosecond timescale. Direct amorphization begins at pressures much lower than what was previously assumed, just above the Hugoniot elastic limit of 5 GPa, with full amorphization to a high-density amorphous phase, observed at 32(10) GPa and 20 ns. Upon release, the material partially recrystallizes back into the original structure, demonstrating a memory effect.

¹Zhongwu Lan,¹Ross N.Mitchell,²Thomas M.Gernon,³Adam R.Nordsvan
Earth and Planetary Science Letters 581, 117407 Link to Article [https://doi.org/10.1016/j.epsl.2022.117407]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²School of Ocean and Earth Science, University of Southampton, Southampton SO22 4JR, UK
³Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong
Copyright Elsevier

The ca. 717 Ma low-latitude Sturtian “snowball Earth” glaciation lasted ∼56 Myr. However, sedimentological evidence for transient, open ocean conditions during the glaciation appears to contradict the concept of a global deep freeze. We demonstrate multiple lines of geologic evidence from five continents for a temporary, localized sea-ice retreat during the middle of the Sturtian glaciation, which coincides with one, perhaps two, asteroid impacts, and arguably more terrestrial impacts as inferred from the lunar impact record. The well-dated Jänisjärvi impact (ca. 687 Ma) is synchronous with repeated volcanic ash falls whose deposition is most parsimoniously interpreted to indicate a partially ice-free ocean. Temporary greenhouse warming caused by the vaporization of sea ice can explain localized glacial retreat within restricted seaways between these continents, where ice flow would have been constricted and sea ice thinnest before impact.