Evidence from correlated Ir/Os and Cu/S for late-stage Os mobility in peridotite xenoliths: Implications for Re-Os systematics

Combined Ir, Os, Cu, and S concentrations from 18 eastern Australian perido tite xenoliths demonstrate systematic variations in Os concentrations with S loss and require a late-stage process capable of fractionating Os from th e geochemically similar Ir. This effect accounts for the greater variabilit y and lower mean Os concentrations observed in peridotite xenoliths as comp ared with massif peridotites and abyssal peridotites. Late-stage mobility o f Os in xenoliths has important implications for interpreting Os isotopic d ata, and strong correlations between Cu/S and Ir/Os may provide a method fo r screening Re-Os data to provide more reliable Os isotopic model ages. The ability of cryptic secondary processes to fractionate some platinum-group elements (PGEs), in this case Ir and Os, must be taken into account before attributing fractionated PGE patterns in xenoliths to primary mantle proces ses.