High-Pressure Sound Velocity of Perovskite-Enstatite and Possible Composition of Earth's Lower Mantle

Abstract

The compressional sound velocity vp for enstitate of polycrystalline specimens was measured at pressures from 40 to 140 GPa by using the optical analyzer techniques under shock loading. The dependence of vp (in units of km/s) on Hugoniot pressure p (in units of GPa) can be described by: ln vp = 3.079 - 0.691 ln p + 0.094 ln2 p. The vp satisfies Birch's law: vp = 6.213 + 1.212ρ, where ρ is corresponding density, indicating that enstatite is stable throughout the conditions of the lower mantle. Here P wave velocity is 0.5% lower and S wave velocity is 2% higher than those of preliminary reference earth model, respectively. It is concluded that the lower mantle is mainly composed of perovskite-(Mg1-x,Fex)SiO3 and only small amount of (Mg1-x,Fex)O is allowed in it.