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

智力上的优点。这项研究旨在研究大洋地幔和热柱成因的科马提岩系统深部地幔中高度亲铁元素(HSE：Ru、Pd、Re、Os、Ir和Pt)的相对和绝对丰度的时间演化。高精度的HSE浓度测量以及187Os/188Os和186Os/188Os同位素比值将被用来检验在3.4Ga期间科马提岩地幔源区的HSE特征是否发生了实质性变化。总共将检验大约150个化学特征良好的太古宙、元古界和显生宙科马提岩样品和矿物分离物，年龄范围从3.5Ga(非洲南部的Barberton和Schapenburg)到89 Ma(哥伦比亚的Gorgona岛)。我们将解决的基本问题包括不同科马提石来源中的HSE是否具有广泛的软骨性，如果不是，则试图发现它们不同的原因。此外，我们将尝试评估在科马提质来源中HSE的绝对丰度是否随时间或地点而变化。其中一些科马提岩的少量现存186Os/188Os、187Os/188Os和HSE数据已经表明确实存在差异。因此，我们将特别针对一些具有异常地幔HSE特征的岩石(例如，Belingwe、Pechenga、Gorgona)，以及更典型的系统，如来自Finish Lapland的科马提岩。差异将在核的可变晚期吸积或高压分离、洋壳再循环、熔体提取和核-地幔相互作用的背景下加以考虑。该项目将对建立仍然有限的关于地幔中HSE丰度的高质量数据库作出重大贡献，特别是在地球演化的头30亿年期间。因此，这项研究的结果可能使我们最终对晚期吸积物质的起源施加化学限制，甚至可能导致对核心热演化的进一步评估。更广泛的影响。这项研究将让一到两名本科生积极参与，作为他们在马里兰大学职业生涯的顶峰研究论文工作的一部分。因此，这里提出的一些研究将有助于向初出茅庐的科学家灌输在岩石学和同位素地球化学中使用的方法。我们的外展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.