Preliminary Nanosims Analysis of Carbon Isotope of Carbonates in Calcium-Aluminum-Rich Inclusions

Carbonate minerals observed in primitive meteorites are products of either terrestrial weathering or aqueous alteration in the early solar system. Most of the carbonate minerals in carbonaceous chondrites occur primarily as isolated grains in matrix, as crosscutting veins, or as replacement minerals in chondrules [e.g., 1, 2]. A few calcium-aluminum-rich inclusions (CAIs) have been reported containing carbonate minerals as well [2, 3]. The C and O isotopes of carbonates in carbonaceous chondrites, mostly measured by stepwise extraction of bulk samples with phosphoric acid [4–7], are largely distinctive from those of terrestrial carbonates, whereas textural and petrographic evidence indicates that some carbonates in primitive meteorites are terrestrial in origin [2]. This study attempts to investigate from the aspect of C isotope the origin of rare carbonate minerals in some CAIs. If of extraterrestrial origin, carbonates in CAIs can provide important information and constraints on the ubiquitous aqueous alteration process in the early solar system.