Large Ca-48 anomalies are associated with Ti-50 anomalies in Murchison and Murray hibonites

Abstract

Ion microprobe measurements of the Ca isotopic compositions of eight individual hibonite grains from the Ca chondrites Murray and Murchison are reported. Large Ca-48 anomalies two orders of magnitude larger than those observed in normal inclusions and at least a factor of four larger than in the FUN inclusions are found. These anomalies are qualitatively correlated with the Ti-50 anomalies in the sense that the delta Ca-48 and delta Ti-50 values have the same sign. These results confirm previous conclusions concerning the presence of a nucleosynthetic component produced by neutron-rich nuclear statistical equilibrium processes. They suggest the preservation of the isotopic anomalies with interstellar dust grains as carriers of the n-rich Ca and Ti components. The large variation in the delta Ca-48/delta Ti-50 ratios indicates multiple nucleosynthetic components and/or chemical fractionation between Ca and Ti prior to hibonite formation.