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arXiv · 2112.06038

Ancient and recent collisions revealed by phosphate minerals in the Chelyabinsk meteorite

Craig R. Walton·Oliver Shorttle·Sen Hu·Auriol S. P. Rae·Ji Jianglong·Ana Černok·Helen Williams·Yu Liu·Guoqiang Tang·Qiuli Li·Mahesh Anand
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Abstract

The collision history of asteroids is an important archive of inner Solar System evolution. Evidence for these collisions is brought to Earth by meteorites, which can preserve impact-reset radioisotope mineral ages. However, as meteorites often preserve numerous mineral ages, their interpretation is controversial. Here, we combine analysis of phosphate U-Pb ages and mineral microtextures to construct a collision history for the highly shocked Chelyabinsk meteorite. We show that phosphate U-Pb ages in the meteorite are independent of thermal history at macro-to-microscales, correlating instead with phosphate microtexture. Isotopic data from pristine phosphate domains is largely concordant, whereas fracture-damaged domains universally display discordance. Combining both populations best constrains upper (4,473 +/- 11 Ma) and lower intercept (-9 +/- 55 Ma, i.e., within error of the present day) U-Pb ages for Chelyabinsk phosphates. We conclude that all phosphate U-Pb ages were completely reset during an ancient high energy collision. Fracture-damaged phosphate domains experienced further Pb-loss during mild collisional heating in the geologically recent past, and must be targeted to properly constrain a lower intercept age. Targeting textural sub-populations of phosphate grains can significantly improve the calculation and interpretation of U-Pb ages, permitting more robust reconstruction of both ancient and recent asteroidal collision histories.

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Craig R. Walton, Oliver Shorttle, Sen Hu, Auriol S. P. Rae, Ji Jianglong, Ana Černok, Helen Williams, Yu Liu, Guoqiang Tang, Qiuli Li, Mahesh Anand. 2022-01-27. Ancient and recent collisions revealed by phosphate minerals in the Chelyabinsk meteorite. https://arxiv.org/abs/2112.06038

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