P-V-T relations of MgSiO3 perovskite determined by in situ X-ray diffraction using a large-volume high-pressure apparatus

The volume of MgSiO3 perovskite has been precisely measured at pressures of 19 to 53 GPa and temperatures of 300 to 2300 K by means of in situ X-ray diffraction in a multi-anvil apparatus. The present results indicate the isothermal bulk modulus K-T0 = 256(2) GPa and its pressure derivative K-T0' = 3.8(2). The fixed Debye temperature theta(0) = 1030 K gives a Gruneisen parameter at ambient pressure gamma(0) = 2.6(1) and its logarithmic volume dependence q = 1.7(1). The pressure derivative of the isothermal bulk modulus, Anderson-Gruneisen parameter and thermal expansion coefficient at ambient pressure are found to be (partial derivative K-T/partial derivative T)(P) = -0.035(2) GPa/K, delta(T) = 6.5(5), alpha(0) = 2.6(1) x 10(-5) + 1.0(1) x 10(-8) (T - 300)/K. Thus the thermal expansion coefficient largely becomes smaller with increasing pressure. The adiabatic geotherm would be fairly large, such as 0.41 K/km at a 660 km depth, and becoming smaller with increasing depth. The temperature and adiabatic geothermal gradient at the bottom of the D' layer would be 2400 K and 0.14 K/km. The buoyancy-driven mantle convection could be very small in the lower part of the lower mantle. Citation: Katsura, T., et al. (2009), P-V-T relations of MgSiO3 perovskite determined by in situ X-ray diffraction using a large-volume high-pressure apparatus, Geophys. Res. Lett., 36, L01305, doi: 10.1029/2008GL035658.