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

洋壳的形成、蚀变和俯冲是地球化学分异过程的基本过程。海洋地壳从火成岩增生到俯冲的化学转变，对制约地球化学演化具有重要意义。虽然上洋地壳的化学成分已经通过多个浅层钻孔进行了研究，但我们对中、下洋地壳的认识仅限于蛇绿岩剖面，很少有深入海洋地壳的钻孔。该项目旨在研究阿曼蛇绿岩最南端地块中已得到充分研究的难熔堆积辉长岩和互补熔岩，这些地块的成分与中洋脊成分谱的枯竭端重叠。本文将验证两个重要的假设：1)下洋壳是洋壳中铂族元素（PGE）的主要储集层；2)熔岩中的平均铼锇比高于相应堆积中的铼锇比。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，并研究热液蚀变对海洋地壳PGE收支的影响。将进行补充同位素、主要元素和微量元素以及岩石学和矿物分析，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、地壳和地幔之间化学相互作用的认识。

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.