Testing Models for the Origin of 186Os/188Os and 187Os/188Os Isotope Variations in the Mantle: Core Signal, Recycled Components, or Intra-mantle Differentiation

该项目旨在确定导致幔源岩石锇同位素组成变化的物理和化学过程。先前的研究表明，夏威夷和戈尔戈纳火山熔岩中的一些锇同位素变化可能反映了地球和火山之间的化学相互作用。S地幔和地核。如果得到证实，这将对地球的化学和热演化产生广泛的影响。室内。因此，通过详细的研究来验证这一假设对于地质学界来说是非常重要的。锇同位素受到铼和铂的放射性衰变的影响，因此地质物质中锇同位素的变化反映了地球内部不同部分铂/锇和铼/锇比率的长期分异。除了核幔相互作用外，还有几种不同的过程可以影响不同地幔储层的锇同位素组成。这些过程包括通过板块构造将海洋地壳和沉积物再循环到地幔中，古代地幔融化和熔体提取，以及在今天的熔体生成过程中地幔中不同岩石类型的融化。因此，锇同位素的变化可以为几个地质过程提供重要的限制，这些地质过程帮助塑造了地球的化学和物理演化。但前提是能够区分产生这些同位素变化的不同机制。这项研究将检查来自夏威夷和戈尔戈纳岛的熔岩中锇同位素和其他地球化学示踪剂之间的相关性，这些熔岩被认为与深层地幔柱有关，以及几套地幔衍生的橄榄岩，这些橄榄岩的组成范围不同。这些分析将使支持的研究人员能够测试、证实或反驳一些假说，这些假说被用来解释某些羽流衍生的熔岩中1860 o（一种由190Pt衰变产生的同位素）的异常富集。通过将高精度的186Os/188Os数据与互补的同位素、主元素和微量元素数据相结合，支持的研究将测试几种提出的导致地幔物质中186Os/188Os比值升高的机制。选择熔岩套件是因为它们在早期的研究中（夏威夷群岛，戈尔戈纳岛）报告具有较高的1860 / 188o，或者因为它们具有地球化学特征，表明辉石岩或榴辉岩熔融在其产生过程中起重要作用（Australs HIMU熔岩）。橄榄岩样品将有助于约束上地幔Pt/Os和Re/Os比率之间的长期耦合（或缺乏耦合），并阐明熔体枯竭在上地幔190Pt-186Os演化中的作用。综上所述，该研究将对目前提出的不同Pt/Os分选起源和地幔186Os/188Os变化模型施加更强的约束，从而解决地质科学中一个重要且长期存在的争议，并增加190Pt-186Os衰变系统在未来地球化学研究中的实用性。

This project seeks to determine the physical and chemical process(es) responsible for generating variations in the osmium isotopic compositions of mantle-derived rocks. Previous studies havesuggested that some osmium isotope variations in lavas from Hawaii and Gorgona may reflect chemical interaction between the Earth?s mantle and core. If confirmed, this would have wide ranging implications for the chemical and thermal evolution of Earth?s interior. Testing this hypothesis through detailed study is therefore of high importance for the geologic community. Osmium isotopes are affected by the radioactive decay of rhenium and platinum, and so osmium isotope variations in geologic materials reflect long-term fractionation of the platinum/osmium and rhenium/osmium ratios in different portions of the Earth's interior. Several different processes in addition to core/mantle interaction can affect the osmium isotope compositions of different mantle reservoirs. These processes include recycling of oceanic crust and sediments into the mantle through plate tectonics, ancient mantle melting and melt extraction, and melting of distinct rock types in the mantle during melt generation today. Therefore, osmium isotope variations can provide important constraints on several geologic processes that have helped shape the chemical and physical evolution of Earth?s interior, but only if the different mechanisms for generating these isotopic variations can be distinguished. This study will examine correlations between Osmium isotopes and other geochemical tracers in lavas from Hawaii and Gorgona Island, thought to be related to deep-seated mantle plumes, and in several suites of mantle-derived peridotites that span a range in composition. These analyses will allow the supported researchers to test and confirm or refute several hypotheses that have been proposed to explain unusual enrichments in 186Os (an isotope generated by the decay of 190Pt) in some plume-derived lavas. By combining high-precision 186Os/188Os data with complementary isotopic, major, and trace element data, the supported research will test several proposed mechanisms for generation of elevated 186Os/188Os ratios in mantle materials. The selected lava suites are chosen because they either have been reported to possess elevated 186Os/188Os in earlier studies (Hawaiian Islands, Gorgona), or because they possess geochemical characteristics that suggest a significant role for pyroxenite or eclogite melting in their generation (Australs HIMU lavas). The peridotite samples will help constrain the long-term coupling (or lack thereof) between Pt/Os and Re/Os ratios in the upper mantle, and illuminate the role that melt depletion plays in the 190Pt-186Os evolution of the upper mantle. Combined, this study will place stronger constraints on the different models proposed for the origin of Pt/Os fractionation and 186Os/188Os variation in the mantle than is currently possible, thereby addressing an important and longstanding controversy in the Geological Sciences and increasing the utility of the 190Pt-186Os decay system in future geochemical studies.