DI53A-08
High-pressure, temperature elasticity of Fe- and Al-bearing MgSiO3: implications for the Earth’s lower mantle

Friday, 18 December 2015: 15:25
301 (Moscone South)
Shuai Zhang1, Sanne Cottaar2, Tao Liu3, Stephen Stackhouse4 and Burkhard Militzer1, (1)University of California Berkeley, Berkeley, CA, United States, (2)University of Cambridge, Cambridge, United Kingdom, (3)University of Leeds, Leeds, United Kingdom, (4)University of Leeds, School of Earth and Environment, Leeds, LS2, United Kingdom
Abstract:
A good knowledge on the thermoelasticity of the major constitutional minerals, Fe- and Al-bearing MgSiO3 bridgmanite and post-perovskite (pPv), is one of the keys for understanding the lower mantle. However, the available data are scarce. By means of first-principles molecular dynamics simulations that treat all anharmonic effects accurately, we extensively explore the effects of the existence of Fe, including both Fe2+ and Fe3+, and Al on the elastic properties of MgSiO3, at different compositions and atomic distributions, mineral phases, and pressure and temperature conditions that are relevant to the Earth’s lower mantle. Based on these results, we find that the laterally averaged (1D) density and seismic velocities support a pyrolitic composition across the whole lower mantle; we also study the transverse anisotropy of these minerals in a subducting slab near the core-mantle boundary, and confirm that the pPv phase with predominant (001) slip plane matches the seismic anisotropy in the D′′ region independent of the amount of Fe or Al. These results provide a useful resource to investigate the seismic properties of mineral assemblages in the deep mantle and to explore the mineralogical origin of heterogeneities in the lower mantle.