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

该项目旨在确定造成幔源岩石锇同位素组成变化的物理和化学过程。以前的研究表明，夏威夷和戈尔戈纳火山熔岩中的某些锇同位素变化可能反映了地球与地球之间的化学相互作用。的地幔和地核。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。的内部。因此，通过详细的研究来验证这一假设对地质界来说非常重要。锇的同位素会受到铯和铂的放射性衰变的影响，因此地质材料中的锇同位素变化反映了地球内部不同部分的铂/锇和铯/锇比率的长期分馏。除了核幔相互作用外，几种不同的过程也会影响不同地幔储层的锇同位素组成。这些过程包括洋壳和沉积物通过板块构造再循环进入地幔，古代地幔熔融和熔体提取，以及今天熔体生成期间地幔中不同岩石类型的熔融。因此，锇同位素的变化可以提供重要的限制，对几个地质过程，有助于塑造地球的化学和物理演化？的内部，但只有当产生这些同位素变化的不同机制可以区分。这项研究将探讨锇同位素和其他地球化学示踪剂之间的相关性，从夏威夷和戈尔戈纳岛的熔岩，被认为是有关的深源地幔柱，并在几套地幔衍生的橄榄岩，跨越一个组成范围。这些分析将使支持的研究人员能够测试和确认或反驳几种假设，这些假设被提出来解释一些羽状熔岩中186 Os（190 Pt衰变产生的同位素）的异常富集。通过将高精度的186 Os/188 Os数据与补充的同位素、主量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地幔物质中186 Os/188 Os比值升高的机制。选择的熔岩套房，因为他们要么已被报道具有较高的186 Os/188 Os在早期的研究（夏威夷群岛，戈尔戈纳），或因为他们拥有的地球化学特征，表明一个显着的作用，辉石岩或榴辉岩熔融在他们的一代（澳大利亚HIMU熔岩）。橄榄岩样品将有助于限制Pt/Os和Re/Os比值之间的长期耦合（或缺乏耦合），并阐明熔体亏损在上地幔190 Pt-186 Os演化中的作用。结合起来，这项研究将放置更强的约束力的不同模型提出的起源Pt/Os分馏和186 Os/188 Os的变化在地幔比目前可能的，从而解决了一个重要的和长期存在的争议，在地质科学和增加实用程序的190 Pt-186 Os衰变系统在未来的地球化学研究。

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.