Osmium Isotopic Evolution of the Continental Crust

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9628195 Jacobsen This project is to determine the 187Os/186Os ratios in continental crust materials (primarily river suspended loads) to constrain the Os isotopic composition of the continental crust. The PI's will establish the 187Os/186Os variations in relation to the 143Nd/144Nd variations in continental materials. The results will be used to constrain models of crust-mantle differentiation and crustal recycling into the mantel, to provide constraints on the Os isotopic composition of the bulk silicate Earth, and to conduct mass balance considerations for the Os isotopic variations in crust and mantle reservoirs. Measurements will be carried out by N-TIMS isotope dilution methods. Data will be obtained on well characterized samples. The PIs will develop geochemical models for the budgets of Re and Os and their relation to the incompatible, lithophile elements in the depleted mantle, continental crust, and other potentially significant reservoirs in the silicate Earth. The ultimate goal is to understand the geochemical behavior of Re and Os in the Earth's crust-mantle system and the utility of this system as a tracer for crust-mantle evolution processes.