¹Axel Wittmann,²Christian R. Kroemer,³Meenakshi Wadhwa,³Thomas G. Sharp,³Matthijs Van Soest,⁴Trevor Martin,⁴Tyler Goepfert
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14311]
¹Eyring Materials Center, Arizona State University, Tempe, Arizona, USA
²Earth and Planetary Sciences Department, University of California, Davis, California, USA
³School of Earth & Space Exploration, Arizona State University, Tempe, Arizona, USA
⁴Metals, Environmental and Terrestrial Analytical Laboratory, Arizona State University, Tempe, Arizona, USA
Published by arrangement with John Wiley & Sons

We studied lunar regolith breccia meteorite Northwest Africa (NWA) 13967 to explore its mineral and clast inventory with special focus on the ubiquitous occurrence of tissintite-II, a newly recognized, vacancy-rich high-pressure clinopyroxene with a feldspathic, Fe- and Mg-enriched composition. Lithic clasts in NWA 13967 indicate a provenance in the Feldspathic Highlands Terrane on the Moon. Most abundant are cumulate impact melt clasts (“poikilitic granulitic breccias”), granular impact melt rocks, vitric impact melt clasts including impact spherules, and anorthositic clasts, while basalt clasts are rare. The breccia groundmass is mostly fused to flow-textured, vesicular, crystallized impact melt that includes 1 μm corundum crystals and up to 5 μm tissintite-II near the contact with lithic clasts. Rare coesite occurs in moganite clasts entrained in the shock-melted groundmass and rimmed by tissintite-II. Petrographic features of NWA 13967 and its bulk rock chemical composition are most similar to the NWA 8046 clan of lunar meteorites, the largest known lunar meteorite. We discuss mineralogical and petrological characteristics of NWA 13967 to unravel chemical and structural changes of the lunar regolith during shock lithification, which may inform the ongoing exploration of the lunar surface.

¹Jiawei Zhao, ^1,2Long Xiao, ³Zhiyong Xiao, ¹Xiang Wu, ¹Qi He, ⁴Jialong Hao, ⁴Ruiying Li, ⁴Yangting Lin
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.01.021]
¹State Key Laboratory of Geological Processes and Mineral Resources, Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan 430074 China
²State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau
³Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082 China
⁴Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 10029 China
Copyright Elsevier

Zircon has been used to chronicle the geological evolution of the Earth and other planetary bodies. In some circumstances the U-Pb radioisotopic system in zircon can be completely reset by shock metamorphism (e.g. high-pressure phase formation and reversion, and recrystallization), erasing the initial crystallization record and instead recording the impact age. These behaviors of element redistribution accompanied with structure variation in shocked zircon provide pivotal evidence to unravel the extreme impact processes. However, the contributions from a variety of shock effects to element redistribution within shocked zircons are not clear due to the complicated and protracted metamorphic processes associated with an impact event. Here we use high-resolution Nano secondary ion mass spectrometry (NanoSIMS) to show that zircon grains from the Chicxulub impact structure that contain microstructural features such as planar/irregular fractures, zircon twins, reidite and zircon granules, record three main types of element redistribution processes related to shock metamorphism and post-impact modification. The first is the preferential yttrium (Y) enrichments at the zircon-reidite boundaries that is closely related to the formation of the high-pressure polymorph reidite, but the primary zoning is preserved in reidite-bearing zircon. The second process involves shock-related heating, resulting in the solid-state transformation from reidite-bearing zircon to granular zircon, and the growth of neo-formed zircon granules. This process facilitates the loss of radiogenic lead (Pb) and allows the retain of primary zoning of uranium (U) in granular zircon due to the different element diffusion properties, thus providing the chance to date the impact event. Thirdly, the studied zircon grains within the Chicxulub impact structure experienced post-impact hydrothermal alteration to varying degrees by localized element incorporation of additional yttrium (Y), titanium (Ti), uranium (U), lead (Pb) and phosphorus (P). The U-Pb systematics altered by post-impact hydrothermal processes reveal a generally discordant line affected by the external input of U and common Pb, which could be an alternative mechanism of localized age resetting happened in shocked zircon grains. Particularly, this study demonstrates the systematic characteristics of element redistribution in shocked zircons that experienced the sequential metamorphic processes from reidite formation to growth of zircon granules, and subsequent hydrothermal alteration within the Chicxulub impact structure. These findings provide the effective constraints for behaviors and mechanisms of element redistribution and age resetting in zircon under extreme shock and post-impact metamorphic conditions in terrestrial impact craters.