Oxygen Reservoirs in the Early Solar Nebula Inferred from an Allende CAI

Abstract

Ultraviolet laser microprobe analyses of a calcium-aluminum–rich inclusion (CAI) from the Allende meteorite suggest that a line with a slope of exactly 1.00 on a plot of δ 17 O against δ 18 O represents the primitive oxygen isotope reservoir of the early solar nebula. Most meteorites are enriched in 17 O and 18 O relative to this line, and their oxygen isotope ratios can be explained by mass fractionation or isotope exchange initiating from the primitive reservoir. These data establish a link between the oxygen isotopic composition of the abundant ordinary chondrites and the primitive 16 O-rich component of CAIs.