¹Megumi Matsumoto,^2,3,4Akira Tsuchiyama,⁵Akira Miyake,⁶Motoo Ito,²Junya Matsuno,⁷Kentaro Uesugi,⁷Akihisa Takeuchi,⁸Yu Kodama,⁷Masahiro Yasutake,⁹Epifanio Vaccaro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.024]
¹Department of Earth and Planetary Materials Science, Tohoku University, Miyagi 980-8578, Japan
²Research Organization of Science and Technology, Ritsumeikan University, Shiga 525-8577, Japan
³CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, China
⁴CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
⁵Division of Earth and Planetary Sciences, Kyoto University, Kyoto 606-8502, Japan
⁶Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kochi 783-0093, Japan
⁷Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan
⁸Marine Works Japan Ltd., Kanagawa 237-0063, Japan
⁹Department of Earth Sciences, The Natural History Museum, London SW7 5BD, U.K
Copyright Elsevier

Cosmic symplectites (COSes), consisting mainly of nanoscaled symplectic intergrowths of magnetite and Fe-Ni sulfides, have extremely heavy oxygen isotopic compositions and are considered tracers of 16O-poor primordial ice in the early solar system. We examined the three-dimensional microstructure and mineralogy of one COS particle, COS#1, in the Acfer 094 carbonaceous chondrite and investigated its origin. Synchrotron-radiation based X-ray computed nanotomography revealed a presence of micro-inclusions inside COS#1. The largest inclusion consists mainly of high-temperature phases of anhydrous sodium sulfate (Na2SO4) and elemental sulfur, which seem to have been formed from a Na2SO4-S eutectic melt. COS#1 showed a trilayered structure surrounding the large inclusion: the innermost coarse-grained layer consisting mainly of 100–200 nm-sized magnetite and Fe-sulfide, the symplectite layer consisting mainly of nanoscaled symplectic intergrowths of magnetite and Fe-Ni sulfides, and the outermost Fe-oxide layer. The symplectite layer comprises the major volume of COS#1 and shows the pseudomorphic structure of precursor Fe-Ni metal grains. The coarse-grained layer seems to have been formed via metal–salt interaction (hot corrosion) at high temperatures, where the precursor Fe-Ni metals contacted with the Na2SO4-S melt. The symplectite formed simultaneously with the coarse-grained layer due to high-speed diffusion of sulfur and oxygen inside the metal grains. The high-temperature metal–salt interactions should have occurred before the incorporation of COS#1 into the meteorite parent body. The precursor of COS#1 should have consisted of Fe-Ni metals and O-Na-S-rich material. The two reductive and oxidative components seem to have formed separately and got together by some mechanical mixing processes in nebula. The COS#1 precursor was heated in a short period and the O-Na-S-rich material melted. The melt induced the hot corrosion of the Fe-Ni metals and was subsequently cooled and solidified. Subsequently, it was incorporated into the meteorite parent body as COS#1. In the parent body, aqueous alteration occurred and formed the outermost Fe-oxide layer on the COS#1 surface.

¹Cheikh Ahmadou Bamba Niang et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13788]
¹Département de Géologie, Université Cheikh Anta Diop, Dakar, Dakar, Senegal
²Institut Fondamental d’Afrique Noire Cheikh Anta Diop, Dakar, Senegal
³Aix-Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

The 10.5-km-diameter, 1 Ma Bosumtwi impact structure in Ghana is one of the youngest, large impact structures known on Earth. The preservation of the morphology of its ejecta deposits, with an annular moat and outer ridge resembling those of rampart impact craters on Mars, makes Bosumtwi a remarkable impact structure on the African continent. An airborne radiometric survey of the southwestern part of Ghana reveals enigmatic circular feature enriched in potassium, coinciding with the crater rim and an outer ejecta ridge at Bosumtwi. The goal of this study is to investigate possible origins of these features, by impact processes (shock metamorphic effects, impact-induced hydrothermal systems) or postimpact surficial processes (erosion, weathering). The origin of these features is discussed here based on field observations, ground-based radiometric measurements, and first cosmogenic nuclide analyses (10Be). The data indicate that the rim and outer ridge were eroded more rapidly than the rest of the impact structure. Accordingly, the downward advance of the weathering fronts in the annular moat, after ejecta emplacement, are responsible for leaching of K from the lateritic residual observed at the surface. The Bosumtwi impact structure is, therefore, a valuable natural laboratory to investigate the factors controlling erosion and weathering processes in the Ashanti belt since impact 1 Ma ago. Simulations of vertical profiles of 10Be concentration further constrain local variations of the erosion rate. In light of this study, circular K anomalies in radiometric surveys might be indicative of potential impact structures in tropical regions.

¹Prieto-delaVega I.,¹García-Florentino C.,¹Torre-Fdez I.,¹Huidobro J.,¹Aramendia J.,¹Arana G.,¹Castro K.,¹Madariaga J.M.
Journal of Raman Spectroscopy (in Press) Link to Article [DOI 10.1002/jrs.6305]
¹Department of Analytical Chemistry, University of the Basque Country UPV/EHU, Bilbao, Spain

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¹Saikia B.J.,²arthasarathy G.,³Borah R.R.
Journal of Earth System Science 131, 38 Link to Article [DOI 10.1007/s12040-021-01803-y]
¹Department of Physics, Anandaram Dhekial Phookan College, Nagaon, 782 002, India
²School of Natural Sciences and Engineering, National Institute of Advanced Studies, Indian Institute of Science Campus, Bengaluru, 560 012, India
³Department of Physics, Nowgong College (Autonomous), Nagaon, 782 001, India

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¹La Cognata M. et al. (>10)
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 826, 136917 Link to Article [DOI 10.1016/j.physletb.2022.136917]
¹Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Catania, 95123, Italy

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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.