Chemical Composition of the Earth's Lower Mantle: Constraints from Elasticity

A long-standing challenge in geophysics and geochemistry has been the inference of the chemical composition of the Earth's lower mantle. Direct comparison of seismological and laboratory-based elasticity data can therefore give us one of the most severe constraints on the mantle mineralogy. Recently remarkable advances in Brillouin scattering spectroscopy have been made using the diamond anvil cell apparatus to explore the sound velocities of lower mantle phases under extremely high-pressure conditions. This chapter focuses on recent technical progress in the determination of sound velocities under high-pressure and/or high-temperature conditions corresponding to the lower mantle. First, the experimental method of Brillouin scattering spectroscopy combined with diamond anvil cell is briefly outlined. Then, representative results on the shear wave velocity measurements of lower mantle phases are reviewed. In the final section, the mineralogical model of lower mantle offered by those new data are discussed.