Equation of state and phase stability of mantle perovskite up to 140 GPa shock pressure and its geophysical implications

We performed shock wave experiments on a natural pyroxene with chemical composition close to (Mg0.92, Fe0.08)SiO3 and initial density of 3.06 g/cm3, between 48 and 140 GPa. The relationship of shock wave velocity us and particle velocity up can been described linearly by us = 3.76(±0.24) + 1.48(±0.07) up (km/s). The model Hugoniot for the assemblage of (Mg0.92, Fe0.08)O (Mw) + SiO2(St) is significantly different from the experimental data, excluding the possibility of chemical decomposition of perovskite to oxides during the shock compression. The Grüneisen parameter γ obtained by fitting the experimental data can be expressed by γ = γ0 (ρ0/ρ)q, where γ0 = 1.84(2) and q = 1.69(3). Using the third‐order Birch‐Murnaghan finite strain equation of state, the shock experimental data yield a zero‐pressure bulk modulus K0s = 260.1(9) GPa and its pressure derivative K′0s = 4.18(4), with ρ0 = 4.19 g/cm3. A comparison of the experimental Hugoniot densities of perovskite with the PREM density profile prefers a perovskite‐dominant lower mantle model.