Geochemical Evolution of the Mantle

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This renewal proposal will apply the Sr, Nd, Pb, and Os radiogenic tracer systems to mantle-derived mafic and ultramafic rocks to further delimit the character of mantle reservoirs, their location in the mantle and their mode of origin and evolution. The P.I.s propose extensive Os isotope studies of oceanic basalts from localities where the end-member mantle reservoirs DMM, EMI, EM 2 and HIMU are most strongly evident. Ultramafic xenoliths from EM 2 and HIMU islands will be analyzed to compare with the associated basalts. The recognition of a new mantle reservoir, proposed to be lower mantle, will be explored by Os isotope tracer studies of basalts from the islands of Ascension and the Cameroon Line. The early stages of mantle evolution (2.5 - 3.7 b.y.) will be studied by Sr, Nd, Pb and Os studies of primary magmatic minerals from Archean mafic rocks. An to utilize the inherent strengths of the Re/Os system in studying both early mantle processes (accretion and core formation) and present-day processes (derivation of plumes from ancient oceanic crust stored in the lower mantle), the P.I.s propose to study the parameters which control the geochemical behavior of Re and Os. This will involve both natural studies of the Re and Os partitioning between magma and mantle minerals (silicate, sulfide, oxide and metal), and experimental studies of Re - Os solubility and partitioning between metal, silicate melt and sulfide liquid.