SiO2-SiC Mixtures at High Pressures and Temperatures: Implications for Planetary Bodies Containing SiC

Abstract

We present results from high-pressure and high-temperature experiments on mixtures of SiC and SiO2 to explore the stability of SiC in the presence of oxygen-rich silicates at planetary mantle conditions. We observe no evidence of the ambient pressure predicted oxidation products, CO or SiO, resulting from oxidation reactions between SiC and SiO2 at pressures up to ~40 GPa and temperatures up to ~2500 K. We observe the decomposition of SiC through releasing C, resulting in vacancies in the SiC lattice and consequently the contracted SiC ambient volume V0 observed in the heated regions of sample. The decomposition is further supported by the observations of diamond formation and the expanded SiO2 V0 in the heated regions of samples indicating the incorporation of C into SiO2 stishovite. We provide a new interpretation of SiC decomposition on laboratory timescales, in which kinetics prevent the reaction from reaching equilibrium. We consider how the equilibrium decomposition reaction of SiC will influence the differentiation of a SiC-containing body on planetary timescales and find that the decomposition products may become isolated during early planetary differentiation. The resulting presence of elemental Si and C within a planetary body may have important consequences for the compositions of the mantles and atmospheres of such planets.