HIGH ABUNDANCES OF CIRCUMSTELLAR AND INTERSTELLAR C-ANOMALOUS PHASES IN THE PRIMITIVE CR3 CHONDRITES QUE 99177 AND MET 00426

QUE 99177 and MET 00426 are the first known CR3 chondrites and have largely escaped the aqueous alteration experienced by most of the CR chondrite group. In addition to high presolar silicate and oxide grain abundances, these meteorites also contain high abundances of phases with anomalous C isotopic compositions. Presolar SiC abundances (similar to 65 ppm) are consistent with independent estimates for CR1 and CR2 chondrites, indicating that aqueous alteration does not destroy SiC, but are significantly higher than earlier abundance estimates based on noble gas contents. Particularly notable are the high abundances (similar to 120 ppm) of carbonaceous matter with anomalous C isotopic compositions that probably formed in cold molecular clouds via ion-molecule reactions. The observation of both C-13-enriched and C-13-depleted compositions suggests that multiple chemical pathways contribute to the formation of this material. The abundance of such material is significantly higher in QUE 99177 and MET 00426 than in other primitive meteorites and attests to the primitive nature of the CR3 chondrites.