¹J.N.Connelly,²A.A.Nemchin,³R.E.Merle,⁴J.F.Snape,³M.J.Whitehouse,¹M.Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.026]
¹Centre for Star and Planet Formation, GLOBE Institute, University of Copenhagen, Øster Voldgade, 5-7, DK-1350, Copenhagen, Denmark
²School of Earth and Planetary Sciences (EPS), Curtin University, GPO Box U1987, Perth, WA 6845, Australia
³Department of Earth Sciences, Natural Resources and Sustainable Development, Uppsala University, Villavägen 16, 75236 Uppsala, Sweden
⁴Faculty of Earth and Life Sciences, VU Amsterdam, De Boelelaan 1085,1081 HV Amsterdam, the Netherlands
Copyright Elsevier

Previous isotope studies of lunar samples have demonstrated that volatile loss was an important part of the early history of the Moon. The radiogenic U-Pb system, where Pb has a significantly lower T_50% condensation temperature than U, has the capacity to both recognize and calibrate the extent of volatile loss but this approach has been hindered by terrestrial Pb contamination of samples. We employ a novel method that integrates analyses of individual samples by Ion Microprobe and Thermal Ionization mass spectrometry to correct for ubiquitous common Pb contamination, a method that results in significantly higher estimates for µ-values (²³⁸U/²⁰⁴Pb) than previously reported. Using this method, six of seven samples of low-Ti basaltic meteorites return µ-values between 1900 and 9600, values that are consistent with a re-evaluation of published results that return µ-values of 510-2900 for both low- and high-Ti basalts. While some degree of fractionation during partial melting may increase µ-values, we infer that the source region(s) for the basalts must also have had elevated µ-values by the time the lunar magma ocean solidified. Models to account for the available initial Pb isotopic compositions of lunar basalts in light of timing constraints from thermal modelling imply that their source regions had a µ-value of at least 280, consistent with the elevated µ-values of lunar basalts and that inferred for their sources. Such high µ-values are attributed to the preferential loss of more than 99% of the Pb over U relative to a precursor with a Mars-like composition in the aftermath of the giant impact. Such an extensive loss of Pb is consistent with previously reported losses of other elements with comparable volatility, namely Zn, Rb, Ga and CrO₂. Finally, our modelling of highly-radiogenic lunar Pb isotopes assuming crystallization of the lunar magma ocean over 10’s of millions of years shows that the elevated µ-values allows for, but does not require, a young Moon formation age.

¹Adrian P.Broz,²Joanna Clark,³Brad Sutter,⁴Doug W.Ming,³ValerieTu,⁵Briony Horgan,⁶Lucas C.R.Silva
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114965]
¹Department of Earth Sciences, University of Oregon, Eugene, OR 97405, United States of America
²Geocontrols Systems – Jacobs JETS Contract, NASA Johnson Space Center, Houston, TX 77058, United States of America
³Jacobs JETS Contract, NASA Johnson Space Center, Houston, TX 77058, United States of America
⁴NASA Johnson Space Center, Houston, TX 77058, United States of America
⁵Department of Earth, Atmospheric and Planetary Science, Purdue University, IN, 47907, United States of America
⁶Environmental Studies Program, Department of Geography, University of Oregon, Eugene, OR 97405, United States of America
Copyright Elsevier

Ancient (4.1–3.7-billion-year-old) layered sedimentary rocks on Mars are rich in clay minerals which formed from aqueous alteration of the Martian surface. Many of these sedimentary rocks appear to be composed of vertical sequences of Fe/Mg clay minerals overlain by Al clay minerals that resemble paleosols (ancient, buried soils) from Earth. The types and properties of minerals in paleosols can be used to constrain the environmental conditions during formation to better understand weathering and diagenesis on Mars. This work examines the mineralogy and diagenetic alteration of volcaniclastic paleosols from the Eocene-Oligocene (43–28 Ma) Clarno and John Day Formations in eastern Oregon as a Mars-analog site. Here, paleosols rich in Al phyllosilicates and amorphous colloids overlie paleosols with Fe/Mg smectites that altogether span a sequence of ~ 500 individual profiles across hundreds of meters of vertical stratigraphy. Samples collected from three of these paleosol profiles were analyzed with visible/near-infrared (VNIR) spectroscopy, X-ray diffraction (XRD), and evolved gas analysis (EGA) configured to operate like the SAM-EGA instrument onboard Curiosity Mars Rover. Strongly crystalline Al/Fe dioctahedral phyllosilicates (montmorillonite and nontronite) were the major phases identified in all samples with all methods. Minor phases included the zeolite mineral clinoptilolite, as well as andesine, cristobalite, opal-CT and gypsum. Evolved H₂O was detected in all samples and was consistent with adsorbed water and the dehydroxylation of a dioctahedral phyllosilicate, and differences in H₂O evolutions between montmorillonite and nontronite were readily observable. Detections of hematite and zeolites suggested paleosols were affected by burial reddening and zeolitization, but absence of illite and chlorite suggest that potash metasomatism and other, more severe diagenetic alterations had not occurred. The high clay mineral content of the observed paleosols (up to 95 wt%) may have minimized diagenetic alteration over geological time scales. Martian paleosols rich in Al and Fe smectites may have also resisted severe diagenetic alteration, which is favorable for future in-situ examination. Results from this work can help differentiate paleosols and weathering profiles from other types of sedimentary rocks in the geological record of Mars.

¹Keisuke Sugiura,²Makiko K.Haba,¹Hidenori Genda
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114949]
¹Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan
²Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8550, Japan
Copyright Elsevier

Mesosiderites are a type of stony-iron meteorites composed of a mixture of silicates and Fe-Ni metals. The mesosiderite silicates and metals are considered to have originated from the crust and metal core, respectively, of a differentiated asteroid. In contrast, mesosiderites rarely contain the olivine that is mainly included in a mantle. Although a giant impact onto a differentiated asteroid is considered to be a probable mechanism to mix crust and metal materials to form mesosiderites, it is not obvious how such a giant impact can form mesosiderite-like materials without including mantle materials. We conducted three-dimensional numerical simulations of giant impacts onto differentiated asteroids, using the smoothed particle hydrodynamics method, to investigate the detailed distribution of mixed materials on the resultant bodies. For the internal structure model of a target body, we used a thin-crust model derived from the magma ocean crystallization model of the asteroid Vesta. We also considered, as another possible internal structure for the target body, a thick crust and a large metal core suggested from the proximity observation of Vesta by the Dawn probe. In the simulations with the former model, excavation of the metal core requires nearly catastrophic impacts and mantle is exposed over large surface areas. Thus, stony-iron materials produced on its surface are likely to include mantle materials, and it is difficult to produce mesosiderite-like materials with this internal structure. Conversely, in the simulations with the latter model, mantle materials are exposed only at impact sites, even when the impacts excavate the metal core, and we confirmed that the formation of a surface with little mantle material and the formation of mesosiderite-like materials are possible from such a surface. Therefore, our simulations suggest that an internal structure with a thick crust and a large core is more likely as a mesosiderite parent body rather than the thin-crust internal structure inferred from the conventional magma ocean model.

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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