Highly siderophile elements and 187Re-187Os isotopic systematics of the Allende meteorite: Evidence for primary nebular processes and late-stage alteration

The 187Re-187Os isotopic systematics of only six out of twenty-four Allende chondritic components analyzed plot within uncertainties of a 4568 Ma primordial reference isochron. The deviations from the expected isochron most likely reflect late-stage, open-system behavior within the last 2 billion years, and, in some cases, could even have resulted from terrestrial alteration. The open-system behavior is most readily observed in small, millimeter-size sub-samples of Allende, consistent with Re and/or Os mobility on that scale.