The goals of this proposed study are to better understand the behavior of platinum group elements (PGEs) during dehydration of the downgoing slab and flux melting of the mantle wedge above it. What are the parent-daughter fractionations that occur and how do these contribute to creation of mantle heterogeneities. Since the Tonga-Lau basin system is intraoceanic, the complications due to continental crust can be avoided. Analyses of Re, PGEs and Os isotopes plus 0 and S isotopes will be done for existing ODP samples from the Tonga system and old Pacific crust that have been characterized for other trace elements and isotope systems. Having a well-characterized suite of representative samples should allow an assessment of the relative contributions of subducted sediments, altered ocean crust, and the mantle wedge in arc and back arc volcanic rocks.
