CSEDI Collaborative Research: Application of Siderophile Elements to Early Earth Processes and Mantle Mixing

亲铁元素是指与硅酸盐相比，对金属有强烈偏好的化学元素。对于地球来说，这些元素的丰度受到金属地核分离的强烈影响，也可能受到早期地球（地幔和地壳）硅酸盐部分特有的过程的影响。本项目将开展亲铁元素浓度、同位素组成观测与地球动力学模拟相结合的协同研究，研究地球早期地幔化学非均质性的起源与演化。这项工作的结果将提高对导致建立地幔中亲铁元素丰度的全球过程的理解，并为地幔的分化和混合历史提供新的见解。一项具体任务将是检查陆相岩石中182W同位素异常的岩石学和年代学范围。作为短命的182Hf （t½= 900万年）的衰变产物，182W的变化可能反映了地球历史最初3000万年中地幔内部发生的过程。古代岩石，如我们已经发现了同位素异常的科马长岩，以及现代岩石，如洋中脊玄武岩、海洋橄榄岩和海洋岛屿玄武岩，都将进行研究。为了补充这项工作，我们将模拟大规模的过程，如岩浆海洋结晶，这些过程有可能产生以元素丰度和分馏度为特征的地幔域，这些元素丰度和分馏度是产生观测到的同位素方差所必需的。该项目将涉及马里兰大学（UMd）本科生参与者的认真贡献。因此，这里提出的一些研究将有助于向崭露头角的科学家灌输同位素地球化学和地球动力学建模的方法，以及结果的呈现。该项目还将涉及两所机构的博士后。该提案的合作性质，以及马里兰大学和卡内基科学研究所的密切关系，将允许频繁、直接的互动，包括地球化学数据采集和地球动力学建模的结果。我和博士后都在做这个项目。

Siderophile elements are those chemical elements with a strong preference for metal compared to silicates. For the Earth, the abundances of these elements were strongly affected by segregation of the metallic core, and also likely affected by processes that occurred exclusively in the silicate portion of the early Earth (mantle and crust). For this project, we will conduct collaborative, synergistic research combining observations of siderophile element concentrations and isotopic compositions, with geodynamic modeling to study the origin and evolution of chemical heterogeneities in Earth's early mantle. The outcome of this work will be an improved understanding of the global processes that led to the establishment of siderophile element abundances in the mantle, as well as provide new insights to the differentiation and mixing histories of the mantle. One specific task will be to examine the petrologic and chronologic extents of 182W isotopic anomalies in terrestrial rocks. As the decay product of the short-lived 182Hf (t½ = 9 million years), variations in 182W likely reflect processes that occurred within the mantle during the first 30 million years of Earth history. Both ancient rocks, such as komatiites for which we have already identified isotopic anomalies, and modern rocks, such as mid-ocean ridge basalts, oceanic peridotites, and ocean island basalts will be examined. Complementary to this work, we will model large-scale processes, such as magma ocean crystallization, with the potential to generate mantle domains characterized by the elemental abundances and fractionations necessary to produce the observed isotopic variances. This project will involve serious contributions from undergraduate participants at the University of Maryland (UMd). As such, some of the research proposed here will help to indoctrinate budding scientists in the methods used in isotopic geochemistry and geodynamic modeling, as well as the presentation of results. The project will also involve postdocs at both institutions. The collaborative nature of the proposal, as well as the close proximity of the UMd and Carnegie Institution for Science, will allow frequent, direct interactions involving both geochemical data acquisition and geodynamic modeling of the results for the PI?s and postdocs working on this project.