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

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

doi:10.1038/s43247-022-00373-1

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. However, as meteorites often preserve numerous impact-reset mineral ages, interpretation of their collision histories is controversial. Here, we combine analysis of phosphate U-Pb ages and microtextures to interpret the collision history of Chelyabinsk—a highly shocked meteorite. We show that phosphate U-Pb ages correlate with phosphate microtextural state. Pristine phosphate domain U-Pb compositions are generally concordant, whereas fracture-damaged domains universally display discordance. Combining both populations best constrains upper (4473 ± 11 Ma) and lower intercept (−9 ± 55 Ma, i.e., within error of present) U-Pb ages. All phosphate U-Pb ages were completely reset during an ancient high energy collision, whilst fracture-damaged domains experienced further Pb-loss during mild and recent collisional re-heating. Targeting textural sub-populations of phosphate grains permits more robust reconstruction of asteroidal collision histories.

Highlights

The collision history of asteroids is an important archive of inner Solar System evolution
Previous Electron Back Scattered Diffraction (EBSD) analyses[21] have revealed that all light lithology phosphate grains display domains of distorted crystal orientation, which is most likely attained during a crystal-plastic recovery process (Fig. 2a), whereas dark lithology merrillites display randomly oriented strain-free sub-domains (Type II recrystallisation)[38], evidencing recrystallisation likely driven by more intensive heating (Fig. 2b)
This specific association of phosphate textures with lithology type suggests the formation of the Chelyabinsk melt rock during a single impact event—an interpretation which is supported by similar observations made for phosphates in terrestrial impactites[25]

Summary

Introduction

The collision history of asteroids is an important archive of inner Solar System evolution. At the 2 σ level, upper and lower intercept age uncertainties obtained using light and dark lithology or pristine and fracture-damaged phosphate populations overlap (Fig. 4).

Results

Conclusion