Elastic Shear Anisotropy of Ferropericlase in Earth's Lower Mantle.

Seismic shear anisotropy in the lowermost mantle most likely results from elastic shear anisotrop and lattice preferred orientation of its constituent minerals, including perovskite, post-perovskite and ferropetidase. Measurements of the elastic shear anisotropy of single-crystal (Mg0.9Fe0.1)O up to 69 gigapascals (GPa) show that it increased considerably across the pressure-induced spin transition of iron between 40 and 60 GPa. Increasing iron content further enhances the anisotropy. This Leads to at least 50% stronger elastic shear anisotropy of (Mg,Fe)O in the lowermost mantle compared to MgO, which is typically used in geodynamic modeling. Our results imply that ferrepericlase is the dominant cause of seismic shear anisotropy in the lower mantle. [ABSTRACT FROM AUTHOR]