ABSTRACT
Recent Re-Os studies of sulfide concentrations in anorthosite-dominated plutonic suites consistently yield high initial 187Os/188Os ratios in sulfide minerals, indicating a major component of crustal Os. These studies have led to three distinct hypotheses for the origin of the sulfide mineralization, with implications for the genesis of the hosting plutonic rocks: (1) the source of the parental magmas is mafic continental crust; (2) mantle-derived melts achieve sulfide saturation and acquire crustal Os through bulk assimilation of silicate crust; or (3) mantle-derived melts achieve sulfide saturation and acquire crustal Os through selective assimilation of crustal sulfur and metals by volatilization and/or melting of crustal sulfides. We favor the third hypothesis on the basis of modeling of Re-Os data together with other geologic and geochemical constraints. Nevertheless, the available data sets are limited, and we cannot yet preclude the possibility that real differences exist among the complexes examined to date.
