Geochemistry of Siderophile and Chalcophile Element in the Earth: Studies on the Distribution of These Elements in Natural and Synthetic Samples

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The process by which the Earth differentiated into a metallic core, a rocky silicate shell, and a liquid/gas envelope is poorly understood. Isotopic studies show that this process began during planetary accretion and ended within a few tens of millions of years. The distribution of elements between the core and surrounding silicate mantle and crust likely occurred under a range of conditions (temperature, pressure, and gas fugacity) and in a variety of settings, including small planetary bodies accreted into the Earth. The integrated result of these conditions is recorded in the current distribution of elements between the core and silicate Earth. By characterizing the composition of these two reservoirs and determining how elements partition themselves between metals and silicates with experiments, we can understand the mechanisms by which the core formed.The results of this three-year study will include analyses of the siderophile (iron-loving) and chalcophile (sulfur-loving) elements in mantle samples (peridotites and pryoxenites), mantle-derived magmas (primitive basalts, komatiites and some of their mineral phases), meteorites (particularly pallasites: asteroidal samples from their core-mantle boundary that are composed of iron metal mixed with olivine crystals) and experimental charges that have been synthesized under specific pressure, temperature and redox conditions. Data for the peridotites, pyroxenites and the magmas will be used to establish the composition of the silicate Earth, which is the primitive mantle composition prior to its differentiation into a crust and mantle system. The meteorite studies will help to establish the fractionation behavior of elements at low pressures and temperatures under various redox conditions. Data from the experimental studies will provide distribution coefficients for elements between minerals and melts, which will further constrain the conditions of core formation. All of these studies will have a broader impact on student mentoring, as well as providing research opportunities for undergraduate and graduate students. The analytical methods have applications in science, industry, medicine, and government and will serve these students well into their careers.