High-pressure, temperature elasticity of Fe- and Al-bearing MgSiO3: implications for the Earth's lower mantle

摘要

Fe and Al are two of the most important rock-forming elements other than Mg,Si, and O. Their presence in the lower mantle's most abundant minerals, MgSiO_3bridgmanite, MgSiO_3 post-perovskite and MgO periclase, alters their elasticproperties. However, knowledge on the thermoelasticity of Fe- and Al-bearingMgSiO_3 bridgmanite, and post-perovskite is scarce. In this study, we performab initio molecular dynamics to calculate the elastic and seismic properties ofpure, Fe^{3+}- and Fe^{2+}-, and Al^{3+}-bearing MgSiO_3 perovskite andpost-perovskite, over a wide range of pressures, temperatures, and Fe/Alcompositions. Our results show that a mineral assemblage resembling pyrolitefits a 1D seismological model well, down to, at least, a few hundred kilometersabove the core-mantle boundary, i.e. the top of the D'' region. In D'', asimilar composition is still an excellent fit to the average velocities andfairly approximate to the density. We also implement polycrystal plasticitywith a geodynamic model to predict resulting seismic anisotropy, and findpost-perovskite with predominant (001) slip across all compositions agrees bestwith seismic observations in the D''.