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 (Mg-0.92, Fe-0.08) SiO3 and initial density of 3.06 g/cm(3), between 48 and 140 GPa. The relationship of shock wave velocity u(s) and particle velocity u(p) can been described linearly by u(sl) = 3.76(+/- 0.24) + 1.48(+/- 0.07) u(p) (km/s). The model Hugoniot for the assemblage of (Mg-0.92, Fe-0.08) 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 Gruneisen parameter g obtained by fitting the experimental data can be expressed by gamma = gamma(0) (rho(0)/rho)(q), where gamma(0) = 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 K-0s = 260.1(9) GPa and its pressure derivative K-0s' = 4.18(4), with rho(0) = 4.19 g/cm(3). A comparison of the experimental Hugoniot densities of perovskite with the PREM density profile prefers a perovskite-dominant lower mantle model.