9711454 Walker This proposal is to continue characterization of the Os isotopic composition of various mantle domains through time, via the analysis of ultramafic rocks that are otherwise geochemically and isotopically well-characterized, and that have relatively high Os concentrations and low Re/Os ratios. Specific issues that Re-Os isotopes may be particularly useful in elucidating are: (1) nature of material added to the Earth via late accretion, (2) the rate at which late accreted materials were homogenized throughout the mantle, (3) the nature and rate at which oceanic crust has been recycled back into certain plum sources, (4) the existence of, and level of chemical exchange between the mantle and outer core, )5) the chronology of development of subcontinental lithospheric keels, and (6) the distribution of highly siderophile elements in various modern and ancient reservoirs. The PI will analyze ultramafic magmatic systems that represent upper oceanic lithospheric materials (Archean through recent ophiolites) and materials derived from likely mantle plumes (Archean and Proterozoic komatiites and ferropicrites). Both whole rock and mineral separates will be analyzed from each location.
