Carbonate formation in meteorite parent bodies: Clues from in-situ C and O isotope analyses

Carbonaceous chondrites show evidence for fluid alteration in planetesimals within a few million years of the Solar Systenm's formation.  To understand the formation conditions of carbonates in CM chondrites, we measured the C and O isotopic composition of Ca-carbinates and the O isotopic composition of magnetite.  These minerals form via direct precipitation from the fluid and/or water-rock interactions in the parent asteroid.  We observe a wide range in the C and O isotope composition of carbonates. 13 C vs 18 O fall into two groups, one consisting of primary calcite and the other consisting of dolomite and secondary calcite.  Our results are consistent with a CO2-CH4 gas mixture as the source of C for carbonate formation.  These gases were likely released during melting of ice in the parent body.   Dolomite and magnetite oxygen isotope fractination are consistent with formation temperatures between 125 +/- 60 C (2SD).  We discuss whether our data support current carbonaceous parent body models.

Speaker: Myriam Telus, UC Santa Cruz