Meteorites & Asteroids

Ancient And Recent Collisions Revealed By Phosphate Minerals In The Chelyabinsk Meteorite

By Keith Cowing
December 14, 2021
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Ancient And Recent Collisions Revealed By Phosphate Minerals In The Chelyabinsk Meteorite
Rock textures in Chelyabinsk. Panels a-c: evolution of Chelyabinsk breccia, from (a) initial formation during shock-melting, brecciation, and shock darkening of host rock material, through (b) solidification into light, dark, and melt lithologies, and (c) subsequent minor disturbances, such as the propagation of fracture networks. Pink symbols represent host-rock phosphate minerals, which are only found in the light and dark lithologies. Photograph used is of Chelyabinsk specimen NHMV-O707; Credit Ludovic Ferriere-NHM Vienna, Austria.`

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.

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

Comments: Accepted in Nature Communication Earth and Environment
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2112.06038 [astro-ph.EP] (or arXiv:2112.06038v1 [astro-ph.EP] for this version)
Submission history
From: Craig Walton
[v1] Sat, 11 Dec 2021 17:50:08 UTC (5,347 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻