The Effects of Carbon Concentration and Silicate Composition on the Metal-Silicate Partitioning of Carbon in a Shallow Magma Ocean

The partitioning of carbon between the core and mantle during the formation of terrestrial planets may have controlled the distribution of carbon in terrestrial planets. However, the abundance of carbon in the Earth's mantle is higher than a prediction based on previous metal-silicate partitioning experiments of carbon at carbon-saturated conditions by more than an order of magnitude. Here, we report new metal-silicate partitioning experiments of carbon at carbon contents of 0.25–0.5 wt%. We show that the metal-silicate partition coefficient of carbon (D^met/sil _C) strongly correlates with nonbridging oxygen per tetrahedral cations (nbo/t) of silicate melts at f_O2 conditions where C-H species are stable. Moreover, the results suggest that D^met/sil _C at carbon-undersaturated conditions may be lower than that at carbon-saturated condition. Thus, D^met/sil _C at low carbon concentrations is essentially important to investigate the distribution of carbon in the Earth during the core formation.