¹J.-C.Viennet,²C.Le Guillou,¹L.Remusat,³F.Baron,¹L.Delbes,²A.M.Blanchenet,¹B.Laurent,¹I.Criouet,¹S.Bernard
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.12.002]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de minéralogie, de physique des matériaux et de cosmochimie, Paris, France
²Univ. Lille, CNRS, INRA, ENSCL, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France
³Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), UMR 7285 CNRS, Université de Poitiers, F-86073 Poitiers Cedex 9, France
Copyright Elsevier

Carbonaceous chondrites contain both soluble and insoluble organic materials (SOM and IOM) which may have been produced in different environments via different processes or share possible genetic relationships. The SOM may have been produced from IOM during hydrothermal episodes on asteroids, and vice versa. The potential role played by the mineral matrix during these episodes (clay minerals of variable crystallinity) remains to be constrained. Here, we exposed a mixture of formaldehyde and glycolaldehyde with ammonia-bearing liquid water together with Fe-rich smectitic minerals to hydrothermal conditions mimicking asteroidal conditions. We used both amorphous gel of smectite or crystalline smectites in order to understand the influence of the crystallinity on the evolution of OM. The organo-mineral experimental residues were characterized at a multiple length scales using X-ray diffraction and microscopy/spectroscopic tools. Results evidence that some IOM polymerizes/condenses in the absence of Fe-rich smectites. Yet, the presence of Fe-rich smectites inhibits this production of IOM. Indeed, the interactions between the SOM and clay surfaces (interlayers or edges) reduce the concentration of SOM available for polymerization/condensation reactions, a necessary step for the production of IOM. In addition, the presence of OM disorganizes the crystallization of the Fe-rich amorphous silicates, leading to smaller crystal sized particles exhibiting a lower permanent charge. This might suggests that the smectite permanent charge distribution may help better constraining the origin and evolution of chondritic clay minerals. Altogether, the present study sheds new light on the organo-mineral interactions having occurred during hydrothermal episodes onto/within chondritic asteroids. Indeed, IOM formation from OM-rich aqueous fluids does not occur during the alteration of amorphous silicates. This would mean that IOM is either produced within pockets free of clay minerals or initially accreted as IOM-rich grain. Last, about ∼50 wt.% of the initial C could not be removed from the clay minerals at the end of the experiments using classical solvent extraction protocols, demonstrating that a high fraction of the SOM in carbonaceous chondrites may have been overlooked.

¹Kevin Robertson,¹Ralph Milliken,¹Carle Pieters,¹Leif Tokle,¹Leah Cheek,¹Peter Isaacson
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114836]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI 02912 2, United States of America
Copyright Elsevier

The primary objective of this work is to constrain the physical and chemical effects of ilmenite on the spectral properties of high‑titanium lunar basalts. Here we use a combination of electron probe microanalysis, x-ray diffraction and VIS-NIR spectroscopy to characterize a suite of Apollo 17 High-Ti lunar basalts and a suite of synthetic laboratory derived binary mixtures to further understand the mixing systematics of opaque Fesingle bondTi oxides in a transparent silicate matrix. We demonstrate how the texture (particle size and shape) and composition (Fesingle bondMg content) of ilmenite exhibit strong controls over the spectral parameters of bulk basalts in the VIS-NIR wavelength range. We show that the presence of fine-grained ilmenite as opposed to coarse-grained ilmenite in high-Ti basalts causes suppression of pyroxene, olivine, and plagioclase absorption features, lowers reflectance values, and induces a stronger ‘red’ spectral slope at wavelengths >1.8 μm. These effects are considerably stronger for samples with fine-grained ilmenite crystals compared with coarse-grained samples that have similar ilmenite abundance. In addition, we show that minor variations in the Mg2+ content of ilmenite significantly alters the strength of the 1 μm feature and the slope above 1.8 μm, which similarly affects the spectral parameters of the bulk basalt. Our results indicate that lunar basalts with lower abundance of fine-grained ilmenite with slightly higher Mg content could exhibit a spectrum with an apparently stronger ilmenite signature when compared to basalts with more abundant, coarser ilmenite. Results presented here suggest that the accuracy of spectral mixing models of remotely sensed data on the Moon would improve by incorporating additional spectral end-members of ilmenite to better represent the compositional variability.

¹David Trang,¹Tyra Tonkham,²Justin Filiberto,¹Shuai Li,³Myriam Lemelin,⁴Catherine M.Elder
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114837]
¹Hawaiʻi Institute of Geophysics and Planetology, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi, United States
²Lunar and Planetary Institute, USRA, Houston, TX, United States
³Département de Géomatique appliquée, Université de Sherbrooke, Québec, Canada
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
Copyright Elsevier

Explosive volcanic eruptions are responsible for producing localized pyroclatic deposits found across the lunar surface. These small localized pyroclastic deposits are thought to have erupted through transient, vulcanian-like eruptions. We used several remote data products, including a water abundance map, to understand the compositional and physical properties of these pyroclastic deposits. Within these deposits, we found strong relationships between water abundance and pyroxene abundance, glass abundance, regolith density scale height, and longitude. These relationships suggest that water abundance can be used to estimate the gas content of an eruption, cooling rate of erupted pyroclasts, optical density of the eruption plume, degree of fragmentation of an eruption, and infer on the distribution of water in the lunar interior. Further, we deduce that the excess water abundance within these pyroclastic deposits represents interior water content, which we tied to other remote measurements that represent important petrological and volcanological parameters to understand eruption dynamics and behavior.

¹Josh Wimpenny,¹Lars Borg,^1,2Corliss Kin I Sio
Earth and Planetary Science Letters 578, 117318 Link to Article [https://doi.org/10.1016/j.epsl.2021.117318]
¹Lawrence Livermore National Laboratory, Livermore, CA 94550, United States of America
²Department of Earth Sciences, University of Toronto, Ontario, Canada
Copyright Elsevier

In this study, we present new Ga isotope data from a suite of 28 mare basalts and lunar highland rocks. The Ga values of these samples range from -0.10 to +0.66‰ (where Ga is the relative difference between the 71Ga/69Ga ratio of a sample and the Ga-IPGP standard), which is an order of magnitude more heterogeneous than Ga values in terrestrial magmatic rocks. The cause of this isotopic heterogeneity must be established to estimate the bulk Ga value of the Moon. In general, low-Ti basalts and ferroan anorthosite suite (FAS) rocks have Ga values that are lower than high-Ti basalts and KREEP-rich rocks. The observation that rocks derived from later forming LMO cumulates have higher Ga values suggests that Ga isotopes are fractionated by processes that operate within the chemically evolving LMO, rather than localized degassing or volatile redistribution.

Correlations between indices of plagioclase removal from the LMO (e.g. Eu/Eu*) with Ga isotope ratios suggest that a Gaplagioclase-melt of -0.3‰, (where Gaplagioclase-melt is the isotopic fractionation associated with crystallization of plagioclase from a melt), could drive the observed isotopic fractionation in high-Ti mare basalts and KREEP-rich rocks. This would be consistent with the observation that FAS rocks have Ga values that are lower than mare basalts. However, the addition of KREEP-like material into the mare basalt source regions would not contribute enough Ga to perturb the isotopic composition outside of analytical uncertainty. Thus, basalts derived from early formed LMO cumulates such as those from Apollo 15, would preserve light Ga isotopic compositions despite containing modest amounts of urKREEP.

We estimate that the Ga value of the LMO was ∼0.14‰ prior to the onset of plagioclase crystallization and extraction. Whether this Ga value is representative of the initial BSM cannot be ascertained from the current dataset. It remains plausible that the Moon accreted with a heavier Ga isotopic composition than the Earth. Alternatively, the Moon and Earth could have accreted with similar isotopic compositions (BSE = 0.00 ± 0.06‰, Kato et al., 2017) and volatile loss drove the LMO to higher Ga values prior to formation of the lunar crust.

¹Chi Ma,²Alexander N. Krot,¹Julie Paque,³Oliver Tschauner,¹Kazuhide Nagashima
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13771]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, 96822 USA
³Department of Geoscience, University of Nevada, Las Vegas, Nevada, 89154 USA
Published by arrangement with John Wiley & Sons

Beckettite (Ca2V6Al6O20; IMA 2015-001) is a newly discovered refractory mineral, occurring as micrometer-sized grains intergrown with hibonite and perovskite, and surrounded by secondary grossular, anorthite, coulsonite, hercynite, and corundum. It occurs within highly altered areas in a V-rich, Type A Ca-Al-rich inclusion (CAI), A-WP1, from the Allende CV3 carbonaceous chondrite. The type beckettite has an empirical formula of (Ca1.99Na0.01)(V3+3.47Al1.40Ti4+0.57Mg0.25Sc0.08Fe2+0.04)(Al5.72Si0.28)O20, with a triclinic structure in space group Purn:x-wiley:10869379:media:maps13771:maps13771-math-0001 and cell parameters a = 10.367 Å, b = 10.756 Å, c = 8.895 Å, α = 106.0°, β = 96.0°, γ = 124.7°, V = 739.7 Å3, and Z = 2, which leads to a calculated density of 3.67 g cm−3. Beckettite’s general formula is Ca2(V,Al,Ti,Mg)6Al6O20 and the endmember formula is Ca2V6Al6O20. Beckettite is slightly 16O-depleted (Δ17O = −16 ± 2‰) compared to the coexisting hibonite and spinel −24 ± 2‰. Beckettite is a primary high-temperature mineral resulting from igneous crystallization of an 16O-rich V-rich CAI melt together with V-bearing hibonite, perovskite, burnettite, spinel, and paqueite. Subsequently, beckettite experienced an incomplete isotope exchange with an 16O-poor aqueous fluid (Δ17O = −3 ± 2‰) on the Allende parent asteroid.

¹Jitse Alsemgeest,¹Fraukje M. Brouwer,²Luis F. Auqué,³Natalia Hauser,³Wolf Uwe Reimold
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13763]
¹Geology and Geochemistry Cluster, Faculty of Science, Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081HV The Netherlands
²Department of Geosciences, University of Zaragoza, Calle Pedro Cerbuna 12, Zaragoza, 50009 Spain
³Laboratory of Geochronology and Isotope Geochemistry, Geosciences Institute, University of Brasília, Brasília, DF, CEP 70910-900 Brazil
Published by arrangement with John Wiley & Sons

Hydrothermal systems provide a possible habitat for early life and are key targets in the quest for life outside Earth. In impact craters on Mars, hydrous minerals can represent products of impact-generated hydrothermal systems (IGHS) or minerals already present in the crust and exposed during impact-caused excavation. Because of its basaltic target rock, similar in composition to Martian crust, the Vista Alegre impact structure in Brazil is one of the very few analog structures that may reveal the origin of these minerals, if evidence of hydrothermal alteration is established. This work presents the results of a systematic search for evidence of hydrothermal alteration at the Vista Alegre impact structure. Four types of alteration were identified, all within a 2.5–3.0 km radius from the crater center: a zircon-bearing melt veinlet, two sets of hydrothermal veins consisting predominantly of calcite and chabazite, and local alteration comprising saponite. Thermodynamic modeling suggests subsequent heating and cooling for each of the hydrothermal vein sets. Combined thermodynamic and spectrometric evidence indicates that development of a vigorous IGHS is unlikely. If similar processes occur on Mars, hydrous minerals are more likely preimpact phases exposed by excavation, rather than being formed through an IGHS.

^1,2Connor D.Hilton,¹Richard D.Ash,¹Richard J.Walker
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.11.035]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742, USA
²Present address: Environmental Signatures Team, Pacific Northwest National Laboratory, Richland, Washington, 99354, USA
Copyright Elsevier

The projected relative abundances of the highly siderophile elements (HSE; Re, Os, Ir, Ru, Pt, and Pd) for bulk parent bodies of 10 magmatic iron meteorite groups/grouplet (IC, IIAB, IIC, IID, IIF, IIIAB, IIIF, IVA, IVB, and South Byron Trio) are broadly similar and show no resolvable differences between noncarbonaceous (NC) and carbonaceous (CC) genetic heritage. The processes driving genetic isotopic heterogeneity in the early Solar System, therefore, evidently did not leave discernable chemical fingerprints with respect to HSE relative abundances on the bulk planetesimal scale. By contrast, the absolute abundances of HSE projected for parent body cores, which reflect core size, are more variable and, on average, higher in CC bodies compared to NC bodies. Overall, bulk core chemical compositions, as well as core size, are linked to the distribution of Fe within a parent body, which is controlled by its oxidation state. The CC parent bodies are constrained to have formed under heterogeneous oxidizing conditions which were, on average, more oxidizing than those of the NC environment.

¹Heng-Ci Tian et al. (>10)
Nature 600, 59-63 Link to Article [DOI https://doi.org/10.1038/s41586-021-04119-5]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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¹Qiu-Li Li et al. (>10)
Nature 600, 54-58 Link to Article [DOI https://doi.org/10.1038/s41586-021-04100-2]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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¹Sen Hu et al. (>10)
Nature 600, 49-53 Link to Article [DOI https://doi.org/10.1038/s41586-021-04107-9]
¹Key Laboratory of the Earth and Planetary Physics, Chinese Academy of Sciences, Beijing, China

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