Oxygen Isotopic Abundances in Calcium- Aluminum-Rich Inclusions form Ordinary Chondrites: Implications for nebular heterogeneity

摘要

The oxygen isotopic composition of two calcium-aluminum-rich inclusions (CALs) from the nuequilibrated ordinary chondrite meteorites Quinyambie and Semarkona are en- riched in ~16O by an amount similar to that in CAIs form carbonaceous chondrites. This may indicate that most CAIs formed in a restributed region of the solar nebula and were then unevenly distributed throughout the various chondrite accretion regions. The Se- markona CAI is isotopically homogeneous and contains highly ~16O-enriched melilite, supporting the hypothesis that all CAI minerals were originally ~16O-rich, but that in most carbonaceous chondrite inclusions some minerals exchanged oxygen isotopes with an external reservoir following crystallization.