Rhenium-Osmium Isotope and Platinum Group Element Systematics of Lower Oceanic Crust

洋壳的形成、改造和俯冲是地球持续化学分异的基本过程。洋壳从火成岩吸积到俯冲的化学转变对制约地球化学演化具有重要意义。虽然利用多个浅层钻孔研究了上洋壳的化学成分，但我们对中、下洋壳的认识仅限于蛇绿岩剖面，而对更深层次洋壳的钻探很少。该项目的目的是研究阿曼蛇绿岩最南端地块中经过充分研究的部分中的难熔堆积辉长岩和补充熔岩，它们在成分上与大洋中脊成分谱枯竭的一端重叠。两个重要的假设将被检验：1)下洋壳是洋壳中铂族元素(PGE)的主要储存库；2)熔岩中的平均Re/Om高于相应堆积体中的Re/Om。该项目还旨在确定重要的PGE载体相，以更好地了解这些元素的岩浆分馏作用，并调查热液蚀变对洋壳PGE收支的影响。将进行补充同位素、常量元素和微量元素以及岩相学和矿物分析，以便将Re/Os/PGE数据置于更广泛的地球化学背景下。这项研究的结果将大大提高我们对海洋、地壳和地幔之间的化学相互作用的理解。

KelemenEAR-0337677Formation, alteration and subduction of oceanic crust are fundamental processes of Earth's ongoing chemical differentiation. The chemical transformations of oceanic crust from igneous accretion to subduction are of fundamental importance to constraining the chemical evolution of the Earth. While the chemical composition of upper oceanic crust has been studied using multiple shallow drill holes, our knowledge of middle and lower oceanic crust is limited to ophiolite sections and few drill holes into deeper oceanic crust. This project is aimed at investigating refractory cumulate gabbros and complementary lavas from well studied sections in the southernmost massifs in the Oman ophiolite, that overlap compositionally with the depleted end of the mid-ocean-ridge compositional spectrum. Two important hypothesis will be tested: 1) The lower oceanic crust is the main reservoir of platinum group elements (PGE) in the oceanic crust, and 2) The average rhenium/osmium in lavas is higher than that in corresponding cumulates. The project also aims at identifying important PGE carrier phases to better understand magmatic fractionation of these elements, and investigating the effects of hydrothermal alteration on the PGE budget of the oceanic crust. Complementary isotope, major and trace element, as well as petrographic and mineral analyses will be carried out to place the Re/Os/PGE data in a broader geochemical context. Results from this study will significantly improve our understanding of chemical interaction between the oceans, crust and mantle.