¹Xue Su,¹Youxue Zhang
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.04.002]
¹Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA
Copyright Elsevier

The H2O concentration and H2O/Ce ratio in olivine-hosted melt inclusions are high in lunar pyroclastic sample 74,220 (H2O up to 1410 ppmw; H2O/Ce up to 77) but lower (H2O 10 to 430 ppmw; H2O/Ce 0.3 to 9.4) in all other lunar samples studied before this work. The difference in H2O concentration and in H2O/Ce ratio is absent for other volatile elements (F, S, and Cl) in melt inclusions in 74,220 and other lunar samples. Because H2O (or H) is a critical volatile component with significant ramifications on the origin and evolution of the Moon, it is important to understand what causes such a large gap in H2O/Ce ratio between 74,220 and other lunar samples. Two explanations have been advanced. One is that volcanic product in sample 74,220 has the highest cooling rate and thus best preserved H2O in melt inclusions compared to melt inclusions in other samples. The other explanation is that sample 74,220 comes from a localized heterogeneity enriched in some volatiles. To distinguish these two possibilities, here we present new data from two rapidly cooled lunar samples with glassy melt inclusions: olivine-hosted melt inclusions (OHMIs) in 79,135 regolith breccia (unknown cooling rate but with glassy MIs similar in texture with those in 74220), and pyroxene-hosted melt inclusions (PHMIs) in 15,597 pigeonite basalts (known high cooling rate, second only to 74,220 and 15421). In addition, we also investigated new OHMIs in sample 74220. If the gap is due to the difference in cooling rates, samples with cooling rates between those of 74,220 and other studied lunar samples should have preserved intermediate H2O concentrations and H2O/Ce ratios. Our results show that melt inclusions in 79,135 and 15,597 contain high H2O concentrations (up to 969 ppmw in 79,135 and up to 793 ppmw in 15597) and high H2O/Ce ratios (up to 21 in 79,135 and up to 13 in 15997), bridging the big gap in H2O/Ce ratio among 74,220 and other lunar samples. Combined with literature data, we confirm that H2O/Ce ratios of different lunar samples are positively correlated to the cooling rates and independent of the type of mare basalts. We hence reinforce the interpretation that the lunar sample with the highest cooling rate best represents pre-eruptive volatiles in lunar basalts due to the least degassing. Based on Ce concentration in the primitive lunar mantle, we estimate that H2O concentration in the primitive lunar mantle (meaning bulk silicate Moon) is 121 ± 15 ppmw. Our new data also further constrain F/P, S/Dy and Cl/Ba ratios in lunar basalts and the lunar mantle. Estimated F, P, and S concentrations in the lunar primitive mantle are 4.4 ± 1.1 ppmw, 22 ± 8 ppmw, and
ppmw, respectively.

^1,2Evan W. O’Neal,¹A.M. Ostwald,¹A. Udry,^3,4J. Gross,⁴M. Righter,⁵T.J. Lapen,⁶J. Darling,⁷G.H. Howarth,¹R. Johnsen,⁵D.R. McQuaig
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.03.016]
¹Department of Geoscience, University of Nevada Las Vegas, Las Vegas NV 89154, USA
²Jacobs Technology, NASA Johnson Space Center (JSC), Houston, TX 77058, USA
³Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA
⁴Department of Earth and Planetary History, American Museum of Natural History, New York, NY 10024, USA
⁵Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, USA
⁶School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth PO1 3QL, UK
⁷Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa
Copyright Elsevier

Martian poikilitic shergottites are cumulate rocks that can help advance the understanding of magmatic evolution from near the base of the crust (∼10 kbar) to near-surface conditions. Through a comprehensive petrographic and geochemical study, we aim to better understand poikilitic shergottite formation and the evolution in the martian interior. A suite of poikilitic shergottites including Northwest Africa (NWA) 7755, NWA 11043, NWA 11065, NWA 10618 and Alan Hills (ALHA) 77,005 were investigated for their major, minor, and trace element compositions of olivine-hosted melt inclusions (MI). The MI occur within both the early-evolutional stage textural and late-evolution stage textural domains in olivine. Major element compositions of MI indicate fractional crystallization between the early and late-crystallizing domains. Calculated parental melt compositions from these MI data yielded results that also petrogenetically link the poikilitic shergottites with the olivine-phyric shergottite subgroup. Trace element compositions of MI show that the later-crystallizing MI could have undergone open-system processes, such as fluid exsolution. Lutetium-Hf and Sm-Nd isotopic analyses were performed on NWA 7755 and NWA 11043 to constrain their age and source isotopic compositions. Northwest Africa 7755 shows a 176Lu/177Hf crystallization age of 223 ± 46 Ma, which fits into the expected range for enriched shergottites of ∼165 Ma to 225 Ma. A similar crystallization age and 176Lu/177Hf and 147Sm/144Nd source composition of NWA 7755 to the other enriched shergottites suggests that this specimen likely shares a long-lived geochemical source with these samples that has lasted for at least 60 Ma. Northwest Africa 11043 shows scatter throughout the Lu-Hf and Sm-Nd isotopic data, suggesting that this sample is not in isotopic equilibrium. This sample was possibly inherited from high-temperature processes, such as incomplete magmas mixing from a similar, but distinct, source. We conducted in situ U-Th-Pb isotope analyses of Ca-phosphate minerals for NWA 11043 and found an unreliable crystallization age of 59.2 ± 138.4 Ma: phosphates are likely recording the period of shock metamorphism related to the ejection event. Consistent crystallization ages and magmatic histories support previous work that suggest there is a common magmatic system on Mars that is responsible for the formation of enriched shergottites.

^1,2,3Akira Tsuchiyama et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.03.032]
¹Research Organization of Science and Technology, Ritsumeikan University, Shiga 525-8577, Japan
²Chinese Academy of Sciences (CAS) Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640, China
³CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
Copyright Elsevier

Samples collected from the surface/subsurface of C-type asteroid 162,173 Ryugu by the Hayabusa2 mission were nondestructively analyzed in three dimensions (3D). Seventy-three small particles (approximately 10–180 µm in size) were observed using X-ray nanotomography, with an effective spatial resolution of approximately 200 nm. Detailed descriptions of these samples in terms of mineralogy, petrology, and variations among particles were reported. The 57 most common particles consisted of a phyllosilicate matrix containing mineral grains, mainly magnetite, pyrrhotite, dolomite and apatite. The remaining particles were mostly monomineralic particles (pyrrhotite, dolomite, breunnerite, apatite, and Mg-Na phosphate) with two unique particles (calcite in a Al2Si2O5(OH)4 matrix, and CaCO3, phyllosilicate, and tochilinite-chronstedtite inclusions in a carbonaceous material matrix). The results confirmed that the samples correspond to Ivuna-type carbonaceous chondrites (CI chondrites) or related materials. Many small inclusions of voids and carbonaceous materials were detected in pyrrhotite, dolomite, breunnerite, and apatite. However, no fluid inclusions were observed, except for those in pyrrhotite that have already been reported. Magnetite exhibited a wide variety of morphologies, from irregular shapes (spherulites, framboids, plaquettes, and whiskers) to euhedral shapes (equants, rods, and cubes), along with transitional shapes. In contrast, the other minerals exhibit predominantly euhedral shapes (pyrrhotite: pseudo-hexagonal plates, dolomite: flattened rhombohedrons, breunnerite: largely flattened rhombohedrons, and apatite: hexagonal prisms) or aggregates of faceted crystals, except for Mg-Na phosphate. The matrices were heterogeneous with variable phyllosilicate particle sizes, Mg/Fe ratios, density (1.7 ± 0.2 g/cm3), nanoporosities (36 ± 9 %), and abundances of nanograins of Fe(-Ni) sulfides. The macroporosity of the particles was estimated as 12 ± 4 %.

The observed textural relationships among the minerals suggest a precipitation sequence of: magnetite (spherulite → plaquette/framboid → rod/equant) → pyrrhotite (pentlandite → pyrrhotite) → apatite → dolomite → breunnerite → coarse phyllosilicates. Fe-bearing olivine (or low-Ca pyroxene) might have precipitated later than dolomite, indicating a high Mg activity in the aqueous solution. This precipitation sequence corresponds to a transition from irregular crystal forms (as seen in some magnetite) to regular forms of euhedral crystals (observed in some magnetite and other minerals). Based on the precipitation sequence and mineral morphologies, together with previously reported observations, a model for aqueous alteration in the Ryugu parent body was proposed as follows: CO2-H2O ice, amorphous silicates (GEMS-like material), and some minerals (mostly metal, sulfides, and anhydrous silicates) accumulated to form the parent body of Ryugu. Amorphous silicates and Fe-Ni metal quickly dissolved into the melted ice to form a highly supersaturated aqueous solution. Poorly-crystalized phyllosilicate and spherulitic magnetite precipitated first, followed by plaquette/framboidal magnetites with decreasing degree of supersaturation due to precipitation. Pseudo-hexagonal pyrrhotite plates were formed by dissolution and reprecipitation under relatively low supersaturation. Subsequently, apatite, dolomite, and breunnerite precipitated in this order in response to decreasing supersaturation.

^1,2Jie-Jun Jing,^3,4Ben-Xun Su,⁵Jasper Berndt,²Hideharu Kuwahara,¹Wim van Westrenen
Geochimica et Cosmochimica Acta (inPress) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.03.028]
¹Department of Earth Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
²Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
³Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029, Beijing, China
⁴University of Chinese Academy of Sciences, 100049, Beijing, China
⁵Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Correnstraße 24, D48149 Münster, Germany
Copyright Elsevier

Fifteen experiments at 1 atm pressure and 1400 °C have been conducted to determine partition coefficients between olivine and silicate melt (
) of the first-row transition elements (FRTEs, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn), Ga and Ge in the system FeO-CaO-MgO-Al2O3-SiO2 (FCMAS). Bulk iron contents are varied between 0 and 10 wt% FeO, and oxygen fugacity ranges from 2 log units below the iron-wüstite buffer (IW-2) to 2 log units above the quartz-fayalite-magnetite buffer (QFM + 2), covering a range of igneous processes involving olivine in terrestrial and lunar conditions. Results show that multi-valent Fe and V are redox-sensitive and more incompatible at oxidizing conditions, consistent with previous studies. The moderately volatile elements (Cu, Zn, Ga and Ge) become more volatile at reducing conditions. No correlation between partition coefficients and oxygen fugacity is observed for other multi-valent (Ti, Cr, Mn) and for homo-valent elements (Sc, Co and Ni). Mostshow no sensitivity to bulk system iron contents, but
is significantly higher in our experiments compared toderived from olivine-melt inclusion pairs in lunar samples with much higher FeO contents.
values are nearly constant at a range of oxygen fugacities above the IW buffer, but abruptly decrease when the system is very reducing (below the IW buffer). As a result,
ratios that are constant (∼0.3) at or above the IW buffer increase significantly (0.72–0.99) at IW-2. Using the newly derived partition coefficients, we re-assess two aspects of lunar basalt generation. First, we conclude that the Cr-rich nature of the olivines in lunar basalts compared to terrestrial basalts must be attributed to the Cr-nature of cumulate mantle source of lunar basalts, linked to the early crystallization of Cr-poor minerals olivine and orthopyroxene in the lunar magma ocean resulting in a shallow Cr-rich cumulates. Second, the higher Co/Ni ratios in olivine in high-titanium lunar basalts compared to olivine in low-titanium lunar basalts suggest the former were formed at more reducing conditions (below the IW buffer).

¹Zaicong Wang et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.03.029]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Copyright Elsevier

The Moon’s mare volcanism predominantly occurs within the Procellarum KREEP Terrane (PKT), which is widely thought to be associated with KREEP components within the lunar interior. The Chang’e-5 (CE-5) mission sampled a young (2 Ga) mare basalt Em4/P58 unit of northern Oceanus Procellarum. The geochemistry of the CE-5 mare basalt enables assessment of mantle source compositions which are essential to understand the thermo-chemical mechanism for prolonged volcanism during secular cooling of the Moon. Geochemical compositions of the CE-5 bulk soil, breccias, and basalt clasts from various depths within the drill core consistently display high concentrations of incompatible trace elements (ITE: ∼ 0.3 × high-K KREEP; ∼ 5 μg/g Th) with KREEP-like inter-element ratios, for example for La/Sm, Nb/Ta, and Zr/Y. Exotic impact ejecta, extensive magma differentiation (<70 % fractional crystallization) and significant assimilation of KREEP materials during magma transit and eruption cannot account for the ITE contents and ratios or radiogenic isotope compositions (e.g., εNdinitial of + 8 to + 9 and εHfinitial of + 40 to + 46) of the CE-5 basalts; instead, partial melting of their mantle source played a dominant role. The Chang’e-5 basalt is a chemically evolved low-Ti mare basalt (Mg# of ∼ 34) with enriched KREEP-like ITE compositions but high long-term time-integrated Sm/Nd and Lu/Hf ratio, which represents a hitherto unsampled type of mare basalt. It formed by melting of an augite-rich mantle source (late-stage magma ocean cumulates containing > 30–60 % augite, and little or no ilmenite), with a small amount of late-stage interstitial melt that resembles KREEP (∼1–1.5 modal %, equivalent to 0.2–0.3 μg/g Th). The voluminous mare basalts making up the Em4/P58 unit (>1500 km3) provide compelling evidence for large-scale, ITE enriched young mare magmatism within Oceanus Procellarum. In combination with remote sensing data and with the unique Th-rich Apollo 12 basalt fragment 12032,366–18 (impact ejecta likely from Oceanus Procellarum), this implies that significant portions of the FeO- and Th-rich mare regions of the western PKT may also have formed in a similar way.

¹Takazo Shibuya,^2,3Yasuhito Sekine,⁴Sakiko Kikuchi,^5,6,2Hiroyuki Kurokawa,³Keisuke Fukushi,⁷Tomoki Nakamura,⁸Sei-ichiro Watanabe
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.03.022]
¹Super-cutting-edge Grand and Advanced Research (SUGAR) Program, Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan
²Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan
³Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
⁴Kochi Institute for Core Sample Research, Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Nankoku, Kochi 783-8502, Japan
⁵Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan
⁶Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
⁷Department of Earth Sciences, Tohoku University, Sendai 980-8578, Japan
⁸Department of Earth and Environmental Sciences, Nagoya University, Nagoya 464-8601, Japan
Copyright Elsevier

Parent bodies of carbonaceous chondrites that initially contained metallic iron potentially exert strong reduction power during aqueous alteration to generate molecular hydrogen in excess of hydrogen solubility in water-rich fluids. The surplus hydrogen escapes from the system, which is subsequently supplied to overlying regions in planetesimals. Based on this concept, we conducted chemical equilibrium modeling of the aqueous alteration and simulated gaseous H2 migration within the icy planetesimal that has a melted mantle and an icy shell during the early stages of radiogenic heating. In the chemical equilibrium modeling, we simulated the aqueous alteration of chondritic rocks at 0–350 °C and a water/rock mass ratio of 0.2–10 with initial CO2 contents of 0–10 mol% in the fluid. The results showed that the mineral assemblage and solution composition change with the temperature, water/rock mass ratio, and initial fluid composition. The reproduced mineral paragenesis and abundance well explain those of carbonaceous chondrites. Furthermore, it was revealed that the initial H2 fugacity of the system influences not only the stability of minerals and solution compositions, but also the preservation potential of organic molecules. Indeed, within these parameter spaces, the modeling results account for the organic/inorganic carbon-rich alterations reported for the Tagish Lake meteorite, Ceres, and Ryugu. Simulations of gaseous H2 migration in a planetesimal revealed that gaseous H2 in the deep interior can be transported to the interface with an icy shell even if the permeability is low. Moreover, it is highly possible that an H2-rich layer would have been widely formed just below the icy shell. Therefore, it is expected that H2-rich regions beneath the ice layer in planetesimals have substantial potential for the synthesis and preservation of organic molecules. These results imply that the alteration of carbonaceous chondrite parent bodies and C-complex asteroids is characterized by not only the type of parent bodies (e.g., formation age and distance from the Sun) but also the locations within their parent bodies.

^1,2Kong, Seongyoung,¹Singh, Prashant,^1,2Sarkar, Arka,^1,2Viswanathan, Gayatri,³Kolen’ko, Yury V.,²Mudryk, Yaroslav,^2,4Johnson, Duane D.,^1,2Kovnir, Kirill
Chemistry of Materials 36, 1665-1677 Link to Article [DOI 10.1021/acs.chemmater.3c03003]
¹Department of Chemistry, Iowa State University, Ames, 50011, IA, United States
²Ames National Laboratory, U.S. Department of Energy, Ames, 50011, IA, United States
³Nanochemistry Research Group, International Iberian Nanotechnology Laboratory, Braga, 4715-330, Portugal
⁴Department of Materials Science & Engineering, Iowa State University, Ames, 50011, IA, United States

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^1,2,3He, Ye et al. (>10)
Aerospace 11, 114 Open Access Link to Article [DOI 10.3390/aerospace11020114]
¹Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²Institutes of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China

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^1,2Masahiko Sato,^3,4Kosuke Kurosawa,²Sunao Hasegawa,⁵Futoshi Takahashi
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007864]
¹Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
²Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
³Department of Human Environmental Science, Kobe University, Kobe, Japan
⁴Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Japan
⁵Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
Published by arrangement with John Wiley & Sons

Knowledge of the shock remanent magnetization (SRM) property is crucial for interpreting the spatial change in a magnetic anomaly observed over an impact crater. This study conducted two series of impact-induced SRM acquisition experiments by varying the applied field intensity (0–400 μT) and impact conditions. Systematic remanence measurements of cube-shaped subsamples cut from shocked basalt containing single-domain titanomagnetite were conducted to investigate the effects of changes in pressure and temperature on the SRM acquisition. The peak pressure and temperature distributions in the shocked samples were estimated using shock-physics modeling. SRM intensity was proportional to the applied field intensity of up to 400 μT. SRM intensity data for peak pressure and temperature of up to 8.0 GPa and 530 K, respectively, clearly show that it increases with increasing pressure and decreases with increasing temperature. The SRM has unblocking temperature components up to a Curie temperature of 510 K, and it easily demagnetizes with alternating field demagnetization. The observed SRM properties can be explained by the pressure-induced microcoercivity reduction and temperature-induced modification of the blocking curve. Although the remanence acquisition efficiency of the SRM is significantly lower than that of the thermoremanent magnetization (TRM), the magnetic anomaly originating from the SRM distribution in a broader region may show a contribution comparable to that of the impact-induced TRM distribution in a narrow region.

¹Evgeny Smirnov
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116058]
¹Evgeny SmirnovBelgrade Astronomical Observatory, Volgina 7, 11060, Belgrade, Serbia
Copyright Elsevier

This study explores how well various machine learning classifiers can identify mean-motion resonances in the main belt using supervised learning. The most popular classifiers are assessed: k-Nearest Neighbours, Decision Tree, Gradient Boosting, AdaBoost, Random Forest, and Naïve Bayes. In contrast to previous studies that often relied on default ML configurations, this research conducts a detailed investigation, fine-tuning, and testing of each classifier across various parameters. The results show that simpler models, especially k-Nearest Neighbours and Decision Tree, perform better than more complex ones, particularly in terms of
scores. The paper provides guides on selecting features, parameters, and training set sizes for optimal classifier performance and outlines a method for developing effective machine-learning models for asteroid classification.