Nature and Scale of Mantle Heterogeneities in Upper Mantle Reservoirs: Evidence from trace element abundances and Os isotopic compositions in the Oman ophiolite

地球化学和同位素证据表明，上地幔，洋中脊玄武岩（MORB）的来源，已耗尽的熔融提取过程中地质时期。有人认为，提取MORB后的残留地幔是一个地球化学均质的储集层。近年来，MORB的Re-Os系统学被用来推测与古洋壳再循环过程有关的亏损大洋上地幔的全球化学不均一性。这些地幔不均匀性的性质和规模，由回收过程引入，是未知的。由于不相容的亲石元素的极度亏损，通过直接分析地幔橄榄岩来研究地幔非均质性是困难的。Re-Os方法非常适合于研究超镁铁（地幔）岩石和探测上地幔中再生的古洋壳，因为Os是与地幔矿物相容的元素，而Re是中度不相容的。肥沃地幔的小程度部分熔融将从源中移除一些Re，从而减少残留物中放射成因187 Os的生长。阿曼蛇绿岩地幔岩石的初步分析表明，大的传播的Os同位素组成表明沿走向的同位素变化的古脊，这表明存在一个高度不均匀的上地幔。拟议研究的目的是确定海洋岩石圈不同岩性的微量元素特征和Os同位素组成，此外，还监测地球化学和同位素herteogeneities的性质和规模。

Geochemical and isotopic evidence indicates that the upper mantle, the source of mid-ocean ridge basalts (MORB), has been depleted by melt extraction processes over geological periods. It has been suggested that the residual mantle, after extraction of MORB, represents a geochemically homogeneous reservoir. Recently, Re-Os systematics of MORB have been used to postulate global chemical heterogeneities of the depleted oceanic upper mantle that is related to the recycling process of ancient oceanic crust. The nature and scale of these mantle heterogeneities, introduced by the recycling processes, is unknown. The study of mantle heterogeneities by the direct analyses of mantle peridotites is difficult because of the extreme depletion of incompatible, lithophile elements. The Re-Os method is ideally suited for studying ultramafic (mantle) rocks and detecting recycled ancient oceanic crust in the upper mantle, as Os an element compatible with mantle minerals, while Re is moderately incompatible. Small degrees of partial melting of a fertile mantle will remove some Re from the source reducing the growth of the radiogenic 187Os in the residue. Our preliminary analyses on mantle rocks of the Oman ophiolite reveal a large spread in Os isotopic compositions suggesting an along-strike isotope variability of the paleo-ridge which suggest the presence of a highly heterogenous upper mantle. The purpose of the proposed study is, to determine the trace element signature and the Os isotopic composition of the different lithologies of the oceanic lithosphere and, in addition, to monitor the nature and scale of the geochemical and isotopic herteogeneities.