Collaborative Research: The Lu-Hf Composition of the Earth and Implications for the Future of Hf Isotope Geochemistry

该研究项目旨在解决目前阻碍Lu-Hf同位素体系应用于地幔和地壳演化的紧迫问题。已知176 Lu的衰变常数值不超过6%，而对于地球分异研究至关重要的块状硅酸盐地球（BSE）的Lu-Hf组成可能在Lu/Hf比上变化约10%，导致对古老岩石的Hf同位素数据的解释大相径庭。建议对（1）球粒陨石中的磷酸盐矿物分离物进行Lu-Hf同位素分析，以限制176 Lu衰变常数，（2）从6- 30克陨石中制备的球粒陨石粉末，以限制BSE。该项目将与Christa Gopel（地球仪de巴黎物理研究所）合作完成，该研究所拥有从磷酸盐中分离磷酸盐的丰富经验。 她将监督和进行矿物分离，使用20年前制造的大量滑石粉，这些滑石粉可从史密森学会获得。化学和质谱工作将在亚利桑那州和华盛顿州之间进行，不会增加NSF的成本。在更广泛的影响方面，这项工作将为培养博士后水平的专业同位素地球化学家做出重大贡献。此外，一个或多个本科生在这两个机构将学习实验室程序和方法的研究要素。

This research project is directed at solving pressing problems that currently hinder the application of the Lu-Hf isotopic system to mantle and crust evolution. The value of the decay constant of 176Lu is known to no better than 6%, and the Lu-Hf composition of the Bulk Silicate Earth (BSE), essential for studies of Earth differentiation, could vary by around 10% in Lu/Hf ratio, leading to vastly different interpretations of Hf isotopic data for old rocks. It is proposed to conduct Lu- Hf isotopic analyses of (1) phosphate mineral separates from chondrite meteorites, to constrain the 176Lu decay constant and (2) powders of chondrites prepared from 6- to 30-gram masses of meteorite, to constrain BSE. This project will be done in collaboration with Christa Gopel (Institut de Physique du Globe de Paris), who has extensive experience separating phosphates from chondrites. She will supervise and conduct mineral separations using powders of large volumes of chondrites made 20 years ago that are available from the Smithsonian Institution. Chemical and mass spectrometric work will be split between Arizona and Washington State, with no resulting increased cost to NSF. In terms of broader impacts, this work will contribute materially to training of professional isotope geochemists at a postdoctoral level. In addition, one or more undergraduate students at both institutions will learn elements of laboratory procedure and approaches to research.