^1,2Ai-Cheng Zhang,¹Hao-Xuan Sun,¹Tian-ran Trina Du,¹Jia-Ni Chen,³Li-Xin Gu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.04.025]
¹State Key Laboratory for Mineral Deposits Research and School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
²CAS Center for Excellence in Comparative Planetology, China
³Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

The behaviors of radiogenic Pb in Zr-minerals are critical for reconstructing the chronological framework for the evolutionary history of our Earth and other planetary bodies. Previous investigations have revealed the presence of Pb nanograins in some terrestrial zircons and attributed it to radiation decay of U and mobilization and accumulation in zircon and a subsequent thermal metamorphic event. However, whether impact, a ubiquitous and fundamental process for the evolution of materials on planetary surfaces, can directly produce Pb nanograins in Zr-minerals remains unknown. Here, we report the discovery of abundant metallic Pb nanograins in zirconolite polycrystalline aggregates in the brecciated lunar meteorite Northwest Africa 8182. We propose that the metallic Pb nanograins and their host zirconolite polycrystalline aggregates formed during shock lithification of the host meteorite, which had a significant impact on micro-scale U-Pb isotopic chronology of shocked Zr-minerals. The formation of metallic Pb nanograins also indicates that a reduction of PbO took place during shock metamorphism.