The PIs will analyze the Re-Os isotopic systematics of Archean komatiites and tonalites-granodiorites; mafic layered intrusions; mantle xenoliths; and recent basalts from mid-ocean ridges, ocean islands and island arcs. The specific goals of these studies are to determine the Os isotopic mantle growth curve; to determine the source of cratonic core rocks; to understand the behavior of Re and Os in igneous systems; to study the formation of the subcontinental mantle and to investigate recycling of oceanic crust within the upper mantle and the role of oceanic crust in island arc volcanism. The Re-Os isotopic system has unique potential to contribute to geochemical studies of the Earth. This system provides new information complementary to that available from the Rb-Sr, SM-Nd and U-Th-Pb systems for several reasons: both Re and Os are siderophile elements, Os is compatible in the mantle while Re generally is incompatible, Os has a relatively high abundance in the mantle compared to the crust and the melting events that form basaltic rocks strongly fractionate Os from Re. The use of the Re-Os isotopic system will provide a greater understanding of the depleted and enriched reservoirs of the convecting mantle and the lithosphere, the creation of ancient continental crust with its lithospheric roots and the role of subducted slab components at convergent margins.
