Calcium isotopic compositions of chondrites

We report mass-dependent and mass-independent Ca isotopic variations in nine chondrites from three groups: carbonaceous, ordinary and enstatite chondrites. There is about 0.25‰ per amu, i.e., 1‰ in Ca/Ca, variation in chondrites: carbonaceous chondrites have the lightest Ca isotopes, enstatite chondrites have modeled bulk Earth like Ca isotopes, and ordinary chondrites are in between. The correlations between mass-dependent Ca isotopic variation and chemical variations in chondrites may reflect variable contributions from different endmembers, including refractory inclusions, in different chondrite groups. In detail, enstatite chondrites and the Earth share similar isotopic characteristics, but are very different in chemical compositions. At the ±1 and ±2 e-unit levels, respectively, there is no measurable Ca or Ca anomaly in bulk chondrites. Carbonaceous chondrites show several e-units of Ca excess. That is, Ca exhibits both mass-dependent and mass-independent isotopic variations in chondrites, similar to O isotopes. The Ca anomaly in bulk chondrites is positively correlated with Ti anomaly, but does not form simple correlation with Cr anomaly, implying multiple supernova sources for these neutron-rich isotopes in the Solar System. Finally, all meteorites with negative DO have either Ca deficits (differentiated meteorites) or Ca excess (carbonaceous chondrites), implying that the Sun with a very negative DO is probably also characterized by Ca anomaly compared to the Earth. CAIs cannot be taken as representative of the initial isotopic compositions of refractory elements like Ca for the Earth–Moon system. 2016 Elsevier Ltd. All rights reserved.