| The Re-Os isotope systematics of the Wellgreen intrusion in the Wrangellia terrane were investigated in an effort to deduce the origin of this mafic-ultramafic sill and its Pt-group element (PGE) deposit. Radiogenic initial Os ratios (1.06-1.82) suggest alteration by hydrothermal fluids that carried radiogenic ;Initial Os isotopic ratios for chromitites from the Stillwater Complex are consistent with derivation from a mantle-derived magma that suffered little or no interaction with the continental crust prior to crystallization. Molybdenite, separated from a sample of the G-chromitite, yields a Re-Os age of 2740 Ma. The presence of molybdenite documents Re, and probably Os, mobilization by hydrothermal fluids that permeated the intrusion shortly after crystallization. Re-Os results demonstrate that more than 95% of the Os, and by inference other PGEs in the Stillwater Complex, derive from the mantle.;Subaerial lavas from La Palma, Canary Islands show a large variation in ;When potentially contaminated low-Os OIBs are screened from the literature data set, HIMU islands show the highest (up to 1.25) Os isotopic signatures. The Pb-Os isotope systematics do not define a simple two-component mixing relationship between ambient mantle and recycled oceanic crust of a single composition. This may be due to variable alteration and subduction-induced perturbation of the U/Pb ratio in the recycled material that forms a component of the HIMU source. |
