Ultrasonic Shear Wave Velocities of MgSiO 3 Perovskite at 8 GPa and 800 K and Lower Mantle Composition

Abstract

Ultrasonic interferometric measurements of the shear elastic properties of MgSiO 3 perovskite were conducted on three polycrystalline specimens at conditions up to pressures of 8 gigapascals and temperatures of 800 kelvin. The acoustic measurements produced the pressure ( P ) and temperature ( T ) derivatives of the shear modulus ( G ), namely (∂ G/∂P ) T = 1.8 ± 0.4 and (∂ G/∂T ) P = −2.9 ± 0.3 × 10 −2 gigapascals per kelvin. Combining these derivatives with the derivatives that were measured for the bulk modulus and thermal expansion of MgSiO 3 perovskite provided data that suggest lower mantle compositions between pyrolite and C1 carbonaceous chondrite and a lower mantle potential temperature of 1500 ± 200 kelvin.