Radiogenic Osmium in the Earth's Mantle

本文旨在验证在夏威夷洋岛玄武岩（OIB）和诺里尔斯克西伯利亚洪水玄武岩中测量的放射性成因Os同位素组成（186 Os/ 188 Os和187 Os/ 188 Os）是否是外核与下地幔相互作用的表现。我们拟通过测量北加州~470 My old Trinity橄榄岩中不同地幔岩性（包括几代辉石岩）中铂族元素（PGE）丰度和Os同位素组成（186 Os/ 188 Os和187 Os/ 188 Os）来验证这一假设。为了了解放射性成因186 Os/ 188 Os特征在地幔源物质中出现的频率和地理范围，我们将测量来自世界各地超镁铁质岩石的砂质富Os PGE合金的Os同位素组成，以及来自阿曼Semail蛇绿岩样带的辉石岩样品。这项工作的智力价值在于可能提供一种新的工具，用于量化富辉石岩岩性对海洋玄武岩形成的贡献。生成的数据集将增加我们对上地幔同位素和亲铁微量元素非均质性特征长度尺度的理解，阐明交代过程在PGE分馏中的作用，提高我们对熔体迁移和熔体/围岩反应的理解，并有助于完善上地幔的PGE收支，有利于地球形成的宇宙化学模型。拟议的研究的更广泛的影响将是为处于职业生涯早期阶段的科学家的发展提供机会。该项目还包含丹麦和美国科学家之间合作的一个重要组成部分，这将有助于加强国际科学合作，并支持两国的学术基础设施。

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.