| Abstract |
Primitive meteorites (chondrites) generally suffered from aqueous alteration in their parent bodies. In this study, we measured the C isotopic ratios (δ13C) of carbonate minerals which formed during aqueous alteration to investigate the carbon source(s) and volatiles which the parent bodies accreted.
We found that the δ13C values of carbonates in CM chondrites range from 20 to 80 ‰, whereas carbonates in Tagish Lake show consistently high δ13C values of ~70 ‰. The carbonate abundance of Tagish Lake (1.3 wt%) is much higher than that of CM chondrites (0.17 wt% on average). If the δ13C variation observed for CM carbonates reflects mixing between at least two carbon reservoirs, Tagish Lake contains a larger amount of a 13C-rich carbon reservoir than CM chondrites. Such a carbon reservoir would be CO2 ice which the parent bodies accreted, and the Tagish Lake parent body likely formed under cold environments of <80 K where CO2 ice can condense. These observations suggest that D-type asteroids currently found in the asteroid belt formed outward of the giant-planet region, and then their orbits have evolved. |
