^1,2,3Xiaohui Fu,¹Haijun Cao,¹Jian Chen,¹Xuting Hou,^1,3Zongcheng Ling,⁴Lin Xu,⁴Yongliao Zou,²Chipui Tang,^3,5Weibiao Hsu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13743]
¹Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209 China
²State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau, China
³CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing, 210034 China
⁴State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100190 China
⁵CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Nanjing, 210034 China
Published by arrangement with John Wiley & Sons

We performed a petrological, mineralogical, and geochemical study of the lunar feldspathic meteorite Northwest Africa (NWA) 11111. This meteorite contains several types of lithic clasts, including feldspathic clasts, mafic-rich clasts, granulites, impact melt breccias, minor basaltic clasts, and highly evolved clasts cemented in a recrystallized fine grain matrix. Both mineral chemistry and geochemical characteristics indicate a lunar origin for NWA 11111. The bulk analysis suggests that NWA 11111 is a typical feldspathic lunar meteorite, which is consistent with its large population of anorthositic clasts and plagioclase fragments. A comparison of geochemical data made by lunar orbiter missions indicates that this meteorite was likely launched from the Feldspathic Highland Terrane on the lunar farside. The chemical zoning, coupled with extensive exsolution lamellae (up to 20 μm in width) occurring in pyroxene across three sections of NWA 11111, demonstrates that this meteorite contains components derived from the surface to about 10 km of lunar crust. Magnesian anorthosite clasts are commonly present in the meteorite, indicating that magnesian anorthosite probably represents an important lithology in the lunar farside crust. Basaltic clasts in NWA 11111 range from a very low-Ti to a low-Ti mare basalt, possibly representing cryptomare on the lunar farside. Although a KREEPy signature for NWA 11111 is not evident, highly evolved clasts containing various silica polymorphs and/or K-feldspar are present. They may originate from late-stage residual liquids. Lithic clasts and mineral fragments within NWA 11111 provide new insights into the diversity of lunar crust lithology and magmatic processes on the lunar farside. This meteorite also offers rocky materials from a wide vertical section of lunar crust.

¹Daiki Yamamoto,²Noriyuki Kawasaki,^1,3Shogo Tachibana,³Michiru Kamibayashi,²Hisayoshi Yurimoto
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.016]
¹Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210, Japan
²Department of Natural History Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
³UTokyo Organization for Planetary Space Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are known as the oldest high-temperature mineral assemblages of the Solar System. The CAIs record thermal events that occurred during the earliest epochs of the Solar System formation in the form of heterogeneous oxygen isotopic distributions between and within their constituent minerals. Here, we explored the kinetics of oxygen isotope exchange during partial melting events of CAIs by conducting oxygen isotope exchange experiments between type B CAI-like silicate melt and 18O-enriched water vapor (PH2O = 5 × 10–2 Pa) at 1420°C. We found that the oxygen isotope exchange between CAI melt and water vapor proceeds at competing rates with surface isotope exchange and self-diffusion of oxygen in the melt under the experimental conditions. The 18O concentration profiles were well fitted with the three-dimensional spherical diffusion model with a time-dependent surface concentration. We determined the self-diffusion coefficient of oxygen to be ∼1.62 × 10–11 m2 s–1, and the oxygen isotope exchange efficiency on the melt surface was found to be ∼0.28 in colliding water molecules. These kinetic parameters suggest that oxygen isotope exchange rate between cm-sized CAI melt droplets and water vapor is dominantly controlled by the supply of water molecules to the melt surface at PH2O <∼10–2 Pa and by self-diffusion of oxygen in the melt at PH2O >∼1 Pa at temperatures above the melilite liquidus (1420–1540°C). To form type B CAIs containing 16O-poor melilite by oxygen isotope exchange between CAI melt and disk water vapor, the CAIs should have been heated for at least a few days at PH2O >10–2 Pa above temperatures of the melilite liquidus in the protosolar disk. The larger timescale of oxygen isotopic equilibrium between CAI melt and H2O compared to that between H2O and CO in the gas phase suggests that the bulk oxygen isotopic compositions of ambient gas at ∼1400°C in the type B CAI-forming region is preserved in the oxygen isotopic compositions of type B CAI melilite. Based on the observed oxygen isotopic composition, we suggest that a typical type B1 CAI (TS34) from Allende was cooled at a rate of ∼0.1–0.5 K h–1 during fassaite crystallization.

^1,2,4Zs Kapui,^2,3A.Kereszturi,⁴S.Józsa,⁵Cs Király,⁵Z.Szalai
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105338]
¹Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Hungary
²Konkoly Thege Miklós Astronomical Institute, Research Centre for Astronomy and Earth Sciences, Konkoly Observatory, Hungary
³European Astrobiology Institute, Strasbourg, France
⁴Eötvös Loránd University, Department of Petrology and Geology, Hungary
⁵Geographical Institute, Research Centre for Astronomy and Earth Sciences, Hungary

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