9709896 Walker The hypothesis that plumes may entrain some outer core material will be tested by examining the coupled 187Re-187Os 190Pt-186Os systematics of plume-derived rocks. 190Pt decays to 186Os, so the Pt/Os of the outer core should be much greater than chondritic, using asteroidal cores as analogs. Limited data suggest that, unlike with the Re-Os system, crustal recycling would likely not significantly affect the Pt/Os ratio of a mixed mantle source. The objectives of this study are to: 1) Precisely measure the 186Os/188Os of a variety of potentially plume-derived rocks for which Pb-Os relations suggest the involvement of non-crustal 187Os-enriched materials, and assess if there is a positive relation between 186Os and 187Os enrichment. 2) Precisely and accurately measure the concentrations of Pt and Pt/Os in a variety of mantle and crustal materials that may be recycled into the mantle. The goal of this aspect of the research is to confirm or deny the preliminary evidence that suggests recycling of crustal materials into the mantle little affects the Pt/Os ratio of mantle-crust mixtures. The ultimate result of this study may be a better understanding of whether there is chemical interaction between the Earth's outer core and lower mantle. ***
