Calcium Solubility of Bridgmanite in Subducted Basalt in Earth's Lower Mantle

The calcium solubility in bridgmanite and the resulting abundance of davemaoite under lower-mantle pressure-temperature conditions have been under debate following a recent report of extensive calcium dissolution in bridgmanite. We experimentally investigated the calcium solubility in bridgmanite in a basaltic composition at pressures up to 125 GPa and temperatures up to 3,520 K. Our experimental data are modeled thermodynamically along the bridgmanite-davemaoite solvus to quantify the calcium solubility in bridgmanite and the davemaoite proportion in basaltic and pyrolitic assemblages along lower mantle geotherms. Our results indicate that bridgmanite hosts only 0.001–0.03 Ca cations per formula unit in the lower mantle, while davemaoite remains as an abundant mineral, accounting for 8 and 25 vol% of pyrolitic and basaltic mineralogical models, respectively, along representative lower-mantle geotherms. Our thermoelastic modeling further indicates that the effect of calcium dissolution on the density and bulk sound velocity of lower-mantle assemblages is negligible.