Comprehensive study of carbon and oxygen isotopic compositions, trace element abundances, and cathodoluminescence intensities of calcite in the Murchison CM chondrite

摘要

We have performed in situ analyses of C and O isotopic compositions, trace element concentrations, and cathodoluminescence (CL) intensities on calcite in Murchison, a weakly altered CM chondrite. We found that the trace element (Mg, Mn, and Fe) concentrations are heterogeneous within single calcite grains. Grain to grain heterogeneity is even more pronounced. The analyzed calcite grains can be separated into two distinct types with respect to their C isotopic ratios, trace element concentrations, and CL characteristics: Calcite grains with higher delta C-13(PDB) values (similar to 7 parts per thousand) have low trace element concentrations and uniformly dark CL, while grains with lower delta C-13(PDB) values (similar to 35 parts per thousand) have higher trace element concentrations and CL zoning. In contrast to the C isotopic ratios, O isotopic ratios are similar for both types of calcites (delta(18)(OSMOW) similar to 34 parts per thousand).