Oxygen isotopic compositions of enstatite chondrites and aubrites

Abstract

Oxygen isotopic compositions have been measured for ten EH chondrites, eight EL chondrites, and nine aubrites. The mean δ18O and δ17O values are: 5.31 and 2.74, 5.57 and 2.96, 5.24 and 2.70, respectively. Within the EH group, more equilibrated meteorites are fractionated toward higher heavy isotope abundances than the less equilibrated meteorites. Small departures of individual meteorites from a common mass fractionation occur for some of the EH samples. The aubrites may be genetically related to either the EH or EL group or to both. Almost all of the measured isotopic compositions are indistinguishable from the terrestrial oxygen isotope fractionation line, suggesting a genetic relationship among the earth, the moon, and the enstatite the meteorites.