Temporal Evolution of Highly Siderophile Element Abundances in Earth's Mantle

智力上的优点。拟议的研究的目的是检查的相对和绝对丰度的高度亲铁元素（HSEs：Ru，Pd，Re，Os，Ir和Pt）在大洋地幔和深地幔来源的地幔柱衍生科马提岩系统的时间演化。高精度测量HSE浓度和187 Os/188 Os和186 Os/188 Os同位素比值将被用来检查是否发生了实质性的变化，HSE特征的地幔来源的科马提岩超过3.4 Ga期间。共收集了约150个化学性质良好的太古代、元古代和中生代科马提岩样品和矿物样品，年龄范围从3.5 Ga（巴伯顿和Schapenburg，S. 89 Ma（哥伦比亚戈尔戈纳岛）将被审查。我们将讨论的基本问题包括不同科马提岩来源中的HSE是否广泛地是非线性的，如果不是，试图发现它们不同的原因。此外，我们将试图评估科马提来源中HSE的绝对丰度是否随时间或地点而变化。一些现有的186 Os/188 Os、187 Os/188 Os和HSE数据已经表明，这些科马提岩确实存在差异。因此，我们将专门针对一些岩石，其中有不寻常的地幔HSE特征的暗示（如Belingwe，佩琴加，戈尔戈纳），沿着更典型的系统，如芬兰拉普兰的科马提岩。差异将在不同的晚期增生或核的高压分离、洋壳再循环、熔体提取和核幔相互作用的背景下加以考虑。该项目将为建立仍然有限的高质量地幔HSE丰度数据库做出重大贡献，特别是在地球演化的前30亿年期间。因此，这项研究的结果可能使我们能够最终对后期吸积材料的起源进行化学约束，甚至可能导致对核心热演化的进一步评估。更广泛的影响。这项研究将涉及一到两名本科生的积极参与，作为他们所需的高级研究论文工作的一部分，他们在马里兰州大学的职业生涯的顶峰研究项目。因此，这里提出的一些研究将有助于向新兴科学家灌输岩石学和同位素地球化学中使用的方法。我们的外联工作还将包括与来自四大洲的科学家合作。

Intellectual merit. The proposed study is aimed at examining the temporal evolution of the relative and absolute abundances of highly siderophile elements (HSEs: Ru, Pd, Re, Os, Ir, and Pt) in oceanic mantle and in deep mantle sources of plume-derived komatiite systems. High precision measurements of HSE concentrations and also 187Os/188Os and 186Os/188Os isotope ratios will be used to examine whether substantive changes have occurred in the HSE characteristics of the mantle sources of komatiites over a 3.4 Ga period. A total of approximately 150 chemically well-characterized Archean, Proterozoic and Phanerozoic komatiite samples and mineral separates spanning a range of ages from 3.5 Ga (Barberton and Schapenburg, S. Africa) to 89 Ma (Gorgona Island, Colombia) will be examined. Basic questions we will address include whether or not the HSE in the sources of the different komatiites are broadly chondritic, and if not, attempt to discover the reasons why they differ. Also, we will attempt to assess whether or not the absolute abundances of HSE in komatiitic sources vary either with time or location. A modicum of existing 186Os/188Os, 187Os/188Os, and HSE data for some of these komatiites already suggests that differences do exist. Consequently, we will specifically target some rocks for which there are hints of unusual mantle HSE characteristics (e.g. Belingwe, Pechenga, Gorgona), along with more typical systems, such as komatiites from Finish Lapland. Differences will be considered within a context of variable late accretion or high-pressure segregation of the core, oceanic crust recycling, melt extraction and core-mantle interaction. This project will make a substantial contribution towards building the still limited high-quality database on HSE abundances in the Earth's mantle, especially during the first 3 billion years of Earth's evolution. As such, the results of this study may allow us to ultimately place chemical constraints on the origin of late accreted materials, and possibly even lead to further evaluation of the thermal evolution of the core. Broader impacts. The study will involve the active participation of one to two undergraduate students as part of their required senior research thesis work, the capstone research project of their career at the University of Maryland. As such, some of the research proposed here will help to indoctrinate budding scientists in the methods used in petrology and isotopic geochemistry. Our outreach efforts also will include collaborations with scientists from four continents.