High-pressure sound velocities and elasticity of aluminous MgSiO₃ perovskite to 45 GPa: Implications for lateral heterogeneity in Earth's lower mantle

Brillouin scattering measurements on aluminous magnesium silicate perovskite, arguably the most abundant phase in Earth, have been performed to 45 GPa in a diamond anvil cell at room temperature, using methanol-ethanol-water and neon as pressure transmitting media. The experiments were performed on a polycrystalline sample of aluminous MgSiO₃ perovskite containing 5.1 ± 0.2 wt.% Al₂O₃. The pressure derivatives of the adiabatic bulk (K_os) and shear (μ_os) moduli are 3.7 ± 0.3 and 1.7 ± 0.2, respectively. These measurements allow us to evaluate whether the observed lateral variations of seismic wave speeds in Earth's lower mantle are due at least in part to a chemical origin. Our results indicate that a difference in the aluminum content of silicate perovskite, reflecting a variation in overall chemistry, is a plausible candidate for such seismic heterogeneity.