Formation of calcium silicate perovskite above the core-mantle boundary during solidification of Earth's magma ocean

Calcium silicate perovskite (CaPv) is the host for many trace elements in the lower mantle. Whether, when, and where it forms during the solidification of the magma ocean is fundamental to understanding the geochemical and geodynamical evolution of the early Earth. We performed first-principles molecular dynamics simulations to investigate the partitioning of Ca (alongside Sr and Ba) between bridgmanite and molten pyrolite and laser-heated diamond anvil cell experiments to replicate the crystallization of pyrolitic melt. Results show that Ca is incompatible in bridgmanite at all relevant crystallization conditions in the lower mantle, indicating a progressive enrichment of Ca in the magma ocean as it solidifies. This leads to the crystallization of CaPv during the final stages of solidification in the deep mantle. Coupled with the low bridgmanite-melt partition coefficients for Sr and Ba, our findings infer that both large ion lithophile elements and their host, CaPv, will be concentrated in the deep mantle at the end of magma ocean solidification.