Mineral-melt calcium isotope fractionation factors constrained using ab initio molecular dynamics simulations and their implications to calcium isotope effects during partial melting in the upper mantle

Abstract

To better constrain the Ca isotope effect during partial melting of Earth’s mantle, we used ab initio molecular dynamic simulations to calculate the equilibrium mineral-silicate melt Ca isotope fractionation factors for the major Ca-bearing minerals of the upper mantle (orthopyroxene, clinopyroxene, olivine, and garnet), as well as plagioclase. We found that mineral-melt Ca isotope fractionation factors are dependent on pressure, temperature, and mineral major element compositions, but not the silicate melt composition. Specifically, our calculations show that under equilibrium, clinopyroxene has a slightly heavier Ca isotope composition compared to silicate melt, consistent with the inference of published research that studied the Ca isotope effects during basaltic magma evolution.