DECORE · Deep Earth Chemistry of the Core

Core formation represents the major chemical differentiation event on the terrestrial planets, involving the separation of a metallic liquid from the silicate matrix that subsequently evolves into the current silicate crust and mantle. The generation of the Earth’s magnetic field is ultimately tied to the segregation and crystallization of the core, and is an important factor in establishing planetary habitability. The processes that control core segregation and the depths and temperatures at which this process took place are poorly understood, however. We propose to study those processes. Specifically, the density of the core is lower than would be expected for pure iron, indicating that a light component (O, Si, S, C, H) must be present. Similarly, the Earth’s mantle is richer in iron-loving (“siderophile”) elements, e.g, V, W, Mo, Ru, Pd, etc., than would be expected based upon low pressure metal-silicate partitioning data. Solutions to these problems are hampered by the pressure range of existing experimental data, < 25 GPa, equivalent to ~700 km in the Earth. We propose to extend the accessible range of pressures and temperatures by developing protocols that link the laser-heated diamond anvil cell with analytical techniques such as (i) the NanoSIMS, (ii) the focused ion beam device (FIB), (iii) and transmission and secondary electron microscopy, allowing us to obtain quantitative data on element partitioning and chemical composition at extreme conditions relevant to the Earth’s lower mantle. The technical motivation follows from the fact that the real limitation on trace element partitioning studies at ultra high-pressure has been the grain size of the phases produced at high P-T, relative to the spatial resolution of the analytical methods available to probe the experiments; we can bridge the gap by combining state-of-the-art laser heating experiments with new nano-scale analytical techniques.