Radiogenic Osmium in the Earth's Mantle

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EAR-0309414 This proposal seeks to test if the proposed radiogenic Os isotopic compositions(186 Os/ 188 Os and 187 Os/ 188 Os) measured in the Hawaiian oceanic island basalts (OIB) and in the Siberian Flood Basalts at Norilsk are manifestations of interaction between the outer core and the lower mantle. We propose to test this hypothesis by measuring platinum-group element (PGE) abundances and Os isotopic compositions (186 Os/ 188 Os and 187 Os/ 188 Os) in a variety of mantle lithologies, including pyroxenites of several generations, in the ~470 My old Trinity Peridotite of northern California. In order to understand the frequency and geographical extent with which radiogenic 186 Os/ 188 Os signatures occur in mantle derived materials, we will measure the Os isotopic composition of placer-derived Os-rich PGE alloys from ultramafic rocks in different localities world wide and in samples of pyroxenite from a transect of the Semail Ophiolite, Oman available to us. The intellectual merit of this work lies in potentially providing a new tool for quantifying the contribution from pyroxene-rich lithologies to the production of oceanic basalts. The generated data set will increase our understanding of the characteristic length scales for isotopic and siderophile trace element heterogeneity in the upper mantle, elucidate the role of metasomatic processes in fractionation of PGEs, improve our understanding of melt migration and melt/wall-rock reactions, and help refine the PGE budget of the upper mantle benefiting cosmochemical models for Earth's formation. The broader impacts of the proposed research will be to provide an opportunity for the development of a scientist in the early stages of his career. This project also contains a strong component of collaboration between Danish and American scientists, which will serve to bolster international scientific collaboration, and support for academic infrastructure in both countries.