Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

摘要

Chronology of aqueous activity on chondrite parent bodies constrains their accretion times and thermal histories. Radiometric Mn-53-Cr-53 dating has been successfully applied to aqueously formed carbonates in CM carbonaceous chondrites. Owing to the absence of carbonates in ordinary (H, L and LL), and CV and CO carbonaceous chondrites, and the lack of proper standards, there are no reliable ages of aqueous activity on their parent bodies. Here we report the first Mn-53-Cr-53 ages of aqueously formed fayalite in the L3 chondrite Elephant Moraine 90161 as 2.4(-1.3)(+1.8) Myr after calcium-aluminium-rich inclusions (CAIs), the oldest Solar System solids. In addition, measurements using our synthesized fayalite standard show that fayalite in the CV3 chondrite Asuka 881317 and CO3-like chondrite MacAlpine Hills 88107 formed 4.2(-0.7)(+0.8) and 5.1(-0.4)(+0.5) Myr after CAIs, respectively. Thermal modelling, combined with the inferred conditions (temperature and water/rock ratio) and Mn-53-Cr-53 ages of aqueous alteration, suggests accretion of the L, CV and CO parent bodies similar to 1.8 - 2.5 Myr after CAIs.