Comprehensive Study of the Platinum-Group Elements (PGE) in Normal and Hotspot Affected Mid Ocean Ridge Basalts

本文将对来自URI疏通岩石收集的中洋脊玄武岩（MORB）玻璃中的一组高度亲铁和亲铜元素进行全面的文献记录和研究，重点是相对分异和系统的地理变化。URI疏浚的岩石收集集中在受附近热点和底层地幔柱影响的异常升高的洋中脊上。到目前为止，文献报道的MORB中PGE含量非常有限，不太系统，主要是由于它们的丰度很低，分析困难。高分辨率，高灵敏度，电感等离子体质谱（HR-ICP-MS）的使用提供了新的分析机会。首先将开发和测试一种同位素稀释/ HR-ICP-MS分析Ir， Ru, Pt, Pd, Re, Ag， Cd和Te的方法，然后对大量MORB玻璃进行分析。同样的玻璃也将分析S（用电子探针）和Se（用放射化学中子活化分析）。重点将是描述morb的亲铁/亲铜元素变化的全部范围，它们的相对分异，并寻求这些元素与Pb， Sr， Nd和He同位素系统，S， Se和Te以及之前在同一玄武岩玻璃上建立的其他地球化学参数之间可能的相关性或解耦合。目的是为我们对海洋地壳和下地幔的PGE含量、PGE中地幔非均质性的长度尺度、熔融条件、地幔柱的来源和地幔动力学的认识提供新的和更大的见解。

A comprehensive documentation and study of a selected group of highly siderophile and chalcophile elements in mid-ocean ridge basalt (MORB) glasses from the URI dredge rock collection will be conducted, with emphasis on relative fractionations and systematic geographical variations. The URI dredged rock collection has focused on unusually elevated mid-ocean ridge affected by nearby hotspots and underlying mantle plumes. So far, PGE contents in MORB reported in the literature have been very limited and not very systematic, primarily due to their very low abundances and resulting analytical difficulties. The use of high resolution, high sensitivity, inductive plasma-mass spectrometry (HR-ICP-MS) is providing new analytical opportunities. An isotopic dilution / HR-ICP-MS method of analysis for Ir, Ru, Pt , Pd, Re, Ag, Cd, and Te will be developed and tested initially, and followed by analyses of a large number of MORB glasses. The same glasses will also be analyzed for S (with the electron microprobe) and Se (by radiochemical neutron activation analysis). The focus will be on delineating the full range of siderophile/chalcophile element variations of MORBs, their relative fractionation and seek possible correlations, or decoupling, between these elements and the Pb, Sr, Nd, and He isotope systems, S, Se and Te, and other geochemical parameters previously established on the very same basalt glasses. The purpose is to gain new and greater insights in our understanding of the PGE content of the oceanic crust and underlying mantle, length-scales of mantle heterogeneities in PGE, melting conditions, sources of mantle plumes and mantle dynamics.