Solid-Melt Partitioning in Fe-Si-O Systems: Investigating the Composition of Earth's Core

The light element budget of Earth's core plays an integral role in sustaining the geodynamo, especially in light of recent high values for thermal conductivity. Many geochemical arguments rely on a balance between Earth reservoirs and chondritic abundances by assuming certain elemental abundances in the core. These assumptions do not robustly agree with seismological observations and geodynamical constraints, so laboratory experiments are needed to simulate the compositions and conditions needed to match observations. We perform melting experiments on Fe-Si-O alloys in a laser-heated diamond-anvil cell. Using 2D multi-wavelength imaging radiometry together with textural and chemical analysis of quenched samples, we measure the high-pressure melting curves and determine partition coefficients of light elements between the melt and the coexisting solid. Quenched samples are analyzed in both map view and cross section using scanning electron microscopy (SEM) and electron microprobe analysis (EPMA) to examine the 3D melt structure and composition. Partitioning of light elements between molten and solid alloys dictates (1) the density contrast at the ICB, which drives compositional convection in the outer core and (2) the temperature of the CMB, an integral parameter for understanding the deep Earth. Preliminary low-pressure experiments suggest that neither oxygen nor silicon partition strongly enough into the liquid to satisfy the density jump at the ICB.