¹Yang He,¹Xiao-Wen Liu,¹Ai-Cheng Zhang
Meteoritics & Planetary Science (in Press) Kink to Article [https://doi.org/10.1111/maps.13817]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023 China
Published by arrangement with John Wiley & Sons

In this study, we report the petrography and mineralogy of a brecciated eucrite Northwest Africa (NWA) 8021, which shows a locally layered texture with one layer containing graphic clasts and Si,Ti-rich regions. The graphic clasts contain rod-like grains of silica phases, augite, K-feldspar, and Ca-phosphate minerals included in anorthite. Some of the clasts contain relatively coarse grains of quartz, K-feldspar, and augite, which are chemically different from the rod-like phases, indicating different origins. All of the augite grains in the graphic clasts have rare earth element (REE) concentrations higher than those in typical eucrites. The bulk Na2O+K2O contents of the graphic clasts are higher than typical eucrites. All of these chemical features indicate that the graphic clasts were probably derived from an evolved parent rock. Low-degree partial melting of the eucritic crust (<10%) is required to generate a melt equilibrated with the REE-rich rod-like pyroxene from the graphic clasts. The Si,Ti-rich regions contain high abundances of silica phases (~52 vol%) and ilmenite (~9 vol%), probably derived from an evolved Si,Ti-rich rock (dacite). The evolved components observed in NWA 8021 are different from other evolved components observed in howardites and indicate more diverse evolution in the eucrite parent body than previously thought.

^1,2Joshua F.Snape,³Alexander A.Nemchin,³Tim Johnson,¹Stefanie Luginbühl,⁴Jasper Berndt,⁴Stephan Klemme,⁵Laura J.Morrissey,¹Wim van Westrenen
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.04.008]
¹Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
²Department of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK
³School of Earth and Planetary Sciences, The Institute of Geoscience Research, Curtin University, Perth, WA 6845, Australia
⁴Institute of Mineralogy, University of Münster, Germany
⁵Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia
Copyright Elsevier

This study presents the results of high pressure and temperature experiments to investigate the mineral–melt trace element partitioning behaviour for minerals predicted to have formed during the crystallisation of the Lunar Magma Ocean (LMO). The focus of this work has been particularly on determining partition coefficients for parent–daughter pairs of radiogenic elements, for LMO-relevant temperatures, pressures and compositions. The new experimental data are compared with previous studies for the same minerals and elements in order to establish best estimates for the partition coefficient of each element for evolving compositions of minerals as predicted in recent studies modelling LMO crystallisation. These estimates are used to calculate evolving parent–daughter ratios in the LMO residual melt and crystallising minerals for the four main long-lived radiogenic isotope systems that have been studied in lunar samples (Rb–Sr, Sm–Nd, Lu–Hf and U–Pb). The calculated 87Rb/86Sr, 147Sm/144Nd, and 176Lu/177Hf ratios are consistent with predictions for the mantle sources of lunar basalts and evolved lithologies. In contrast, it is difficult to explain the wide range of 238U/204Pb source ratios predicted from the Pb isotopic compositions of basaltic lunar samples. Potential explanations for this observation are discussed, with the conclusion that the Moon most likely experienced a significant loss of volatiles (including Pb), towards the end of LMO crystallisation, resulting in the dramatic U–Pb fractionation evidenced by recent sample analyses.

¹Christopher R.M.McFarlane,^1,2John G.Spray
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.04.006]
¹Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
²Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
Copyright Elsevier

In situ laser ablation inductively coupled mass spectrometry (LA ICP-MS) is used to determine the U-Th-Pb age of the phosphates ferromerrillite and apatite in the Los Angeles shergottitic meteorite. The initial 207Pb/206Pb was refined by analyzing K-rich diaplectic glass. LA ICP-MS mapping was used to document zones of elevated U and Th content and to establish textural controls on isotope ages. By critically assessing dispersion in the U-Th-Pb dataset due to Pb-diffusion in phosphates during high-temperature shock metamorphism, and as a result of subsequent terrestrial contamination, we obtain a best-estimate U-Pb age of 169 ± 5 Ma anchored at an initial 207Pb/206Pb of 0.98390 ± 0.00018. This is statistically indistinguishable from a joint-isochron age of 179 ± 6 with initial 208Pb/206Pb of 2.5151 ± 0.0028. These results complement previously determined Rb-Sr and Sm-Nd isotope ages and provide independent evidence for LA having crystallized as a medium-grained basic rock from a thick lava flow or high-level intrusion in the late Amazonian at ∼170 Ma. In the context of martian mantle evolution, the initial common-Pb values suggest that Los Angeles originated from a source (µ2 ∼3.2) that is similar to enriched members of the shergottite meteorite clan. The U-Th-Pb systematics of both ferromerrillite and apatite were locally affected by diffusive Pb-loss in thin U-enriched marginal domains and more profoundly in shock-induced melt pockets where temperatures briefly exceeded 2000°C. The results reveal: (1) how precise U-Pb ages can be attained from phosphates; (2) the importance of microtextural contextualization of isotope data; (3) that the timescales of cooling from shock conditions were sufficient to promote local diffusive re-equilibration of Pb over 10s of microns; and (4) that LA ICP-MS mapping can be used to locate domains with the highest U/Pb and Th/Pb, which increases precision on lower intercept ages and isochron regression lines.

¹L. He,²R. E. Arvidson,¹J. A. O’Sullivan,³R. V. Morris,²T. Condus,²M. N. Hughes,⁴K. E. Powell
Journal of Geophysical Research (Planets)(In Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007092]
¹Department of Electrical and Systems Engineering, Washington University in St. Louis, MO
²Department of Earth and Planetary Science, Washington University in St. Louis, MO
³NASA/Johnson Space Center, Houston, TX
⁴School of Earth and Space Exploration, Arizona State University, AZ
Published by arrangement with John Wiley & Sons

The Mars Reconnaissance Orbiter Compact Imaging Spectrometer for Mars (CRISM) covers the spectral range from 0.362 to 3.92 µm with a midafternoon local solar time data acquisition. For equatorial to midlatitudes, depending on the season and surface materials, wavelengths longer than ∼2.65 µm exhibit spectral radiances on sensor that include sunlight and thermal-emission related terms. We developed a radiative transfer based neural network approach to model both solar and emitted terms in which surface kinetic temperatures are retrieved for each image pixel, together with single scattering albedo (SSA) spectra, over the full CRISM wavelength range. We applied the method to along-track oversampled scene FRT00021C92 over Glen Torridon within Gale Crater, where the Curiosity rover traversed and acquired remote sensing and in-situ data. Synergistic analysis of orbital and rover-based data, coupled with laboratory analyses of ferric-rich smectites, provide a self-consistent set of results for the presence of desiccated nontronite associated with Murray formation mudstones exposed as periodic bedrock ridges located just to the south of Vera Rubin ridge. The desiccated nature is consistent with Curiosity’s CheMin data, which for Glen Torridon drill samples indicate an abundance of nontronite having a collapsed structure resulting from loss of interlayer H2O.

^1,2Candice C. Bedford et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007100]
¹Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
²Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

Aeolian processes have shaped and contributed to the geological record in Gale crater, Mars, long after the fluviolacustrine system existed ∼3 Ga ago. Understanding these aeolian deposits, particularly those which have been lithified and show evidence for aqueous alteration, can help to constrain the environment at their time of deposition and the role of liquid water later in Mars’ history. The NASA Curiosity rover investigated a prominent outcrop of aeolian sandstone within the Stimson formation at the Greenheugh pediment as part of its investigation of the Glen Torridon area. In this study, we use geochemical data from ChemCam to constrain the effects of aeolian sedimentary processes, sediment provenance, and diagenesis of the sandstone at the Greenheugh pediment, comparing the Greenheugh data to the results from previous Stimson localities situated 2.5 km north and >200 m lower in elevation. Our results, supported by mineralogical data from CheMin, show that the Stimson formation at the Greenheugh pediment was likely sourced from an olivine-rich unit that may be present farther up the slopes of Gale crater’s central mound. Our results also suggest that the Greenheugh pediment Stimson formation was cemented by surface water runoff such as that which may have formed Gediz Vallis. The lack of alteration features in the Stimson formation at the Greenheugh pediment relative to those of the Emerson and Naukluft plateaus suggests that groundwater was not as available at this locality compared to the others. However, all sites share diagenesis at the unconformity.

¹Huidobro, Jennifer,^1,2Aramendia, Julene,¹Arana, Gorka,¹Madariaga, Juan Manuel
Analytica Chimica Acta 1197, 339499 Open Access Link to Article [DOI 10.1016/j.aca.2022.339499]
¹Department of Analytical Chemistry, University of the Basque Country (UPV/EHU), P.O. Box 644, Bilbao, 48090, Spain
²Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Aarhus, DK-8000, Denmark

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¹Lv, Chaojia,^1,2Liu, Jin
Acta Geochimica (in Press) Link to Article [DOI 10.1007/s11631-021-00522-x]
¹Center for High Pressure Science and Technology Advanced Research, Beijing, 100094, China
²CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Li, Chun-Hui
Acta Geochimica (in Press) Link to Article [DOI 10.1007/s11631-021-00517-8]
¹International Research Center for Planetary Science, College of Earth Sciences, Chengdu University of Technology, Chengdu, China

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^1,2A.P.Jordan,³A.W.Case,^1,2J.K.Wilson,¹C.-L.Huang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115011]
¹Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
²Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, USA
³Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Copyright Elsevier

The standard view of space weathering on the Moon is that the solar wind and micrometeoroid impacts alter the optical properties of lunar soil. A third process—dielectric breakdown driven by solar energetic particles (SEPs)—has also been suggested to contribute to space weathering. It has been difficult to determine the relative roles of these processes. The Earth’s magnetotail, however, provides a way to distinguish between them, because it affects only charged particles. Earth’s magnetotail blocks the solar wind, and here we show that it also likely reduces the flux of SEPs traveling across the tail and impacting the tail-facing hemisphere of the Moon when it is entering or leaving. Consequently, we make two predictions that distinguish how the tail affects dielectric breakdown weathering patterns from how it affects solar wind weathering patterns. First, the magnetotail should create two minima in the total amount of breakdown weathering that has occurred: one near  and a deeper one near  longitude. Second, the tail should create east–west asymmetries in the breakdown weathering of crater walls, with the greatest asymmetries occuring at  longitude. Although the first prediction has proven difficult to test, we find that the second prediction is supported by observations. Therefore, we conclude that investigations of space weathering must consider, not only micrometeoroid and solar wind bombardment, but also dielectric breakdown.

¹William H.Farrand,²Christopher S. Edwards,²Christian Tai Udovicic
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115021]
¹Space Science Institute, 4765 Walnut Street, Suite B, Boulder, CO 80301, USA
²Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, USA
Copyright Elsevier

The Tacquet Formation (TF) was first identified in geologic mapping of southern Mare Serenitatis as a distinct low albedo region split by the linear Rimae Menelaus rilles. A distinct western dome, split by a linear rille and less distinct eastern dome (the Menelaus domes) are also present within the TF. Previous Earth-based radar analyses showed that the TF has a lower circular polarization ratio consistent with a pyroclastic mantle. In this study, compositional and spectroscopic parameters were derived from Moon Mineralogy Mapper (M3) data. Lunar Reconnaissance Orbiter Camera Wide Angle Camera (LROC WAC) and SELENE Kaguya Multiband Imager (MI) multispectral data were also utilized. FeO derived from MI data for the TF and Menelaus domes was elevated at levels consistent with pyroclastic glasses. While not diagnostic of pyroclastics, TiO2 derived from LROC WAC data over the TF and Menelaus domes was also elevated relative to the background materials. Analysis of 1 and 2 μm band parameters also show the TF and Menelaus domes as being distinct with a band center moderately longer than 1 μm and 2 μm band center shorter than the surroundings, characteristics consistent with pyroclastic glass and/or increased ilmenite. M3 data thermally corrected via two different thermal correction approaches indicate a moderately deeper band in the 3 μm region indicative of OH and/or H2O, a characteristic that is also potentially associated with pyroclastic deposits. These compositional findings are consistent with the Earth-based radar data suggesting that the TF is a pyroclastic mantle and potentially represents a previously unrecognized sub-class of pyroclastic deposits associated with lunar volcanic domes.