CSEDI Collaborative Research: Experimental Constraints on the Chemistry and Evolution of Earth's Core

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The chemistry of iron-rich hexagonal close packed (hcp) alloy, and its role in the elemental and isotopic composition, convection, and evolution of the Earth's core, will be studied. The composition of coexisting iron-rich hcp-alloys and melt will be determined at pressures to 25 GPa. The hcp structure of the metal will be stabilized by alloying Fe with a small amount of Os or Ru; this phase is widely thought to be directly relevant to the Earth's core but has been inaccessible in previous experimental studies of chemical partitioning. Data on trace element partitioning between Fe-rich hcp alloy and melt at high pressures will provide insight into the distribution of siderophile elements that act as important radioisotope geochronometers, and will place needed experimental constraints on models of Earth evolution that involve isotopic signatures to be carried from the outer core to the surface. The partitioning of major elements such as Ni, S, and O between Fe-rich hcp alloy and melt will be used to constrain the compositions of the solid inner and liquid outer core, and will improve our understanding of the driving mechanism for compositional convection in the core. The proposed research will be the first application in which Fe is alloyed specifically to stabilize the hcp phase at more amenable pressures and temperatures, and it may stimulate further experimental investigations into the physical and chemical character of hcp-Fe. Additionally, this work will demonstrate a combination of high-pressure experimental and trace element analytical techniques, and should stimulate its broader application in the geosciences. Results from the proposed study will be disseminated primarily through publication in the scientific literature, by participation at scientific conferences, and when warranted, through wider-reaching news outlets.