Molecular Dynamics(MD) simulation of the elasticity of MgSiO3 perovskite and the temperature anomaly in the lower mantle.

Abstract

We performed the molecular dynamics simulation of the elastic properties of MgSiO3 perovskite under the lower mantle conditions to estimate the temperature anomalies in the Earth's interior. The simulated P and S wave velocity anomalies corresponding to the temperature anomaly of 500 K are ±1.11% and ±1.13% respectively at the top of the layer, and are ±0.75% and ±0.78% respectively at the core-mantle boundary. Seismologically observed ratios of the P and S wave velocity anomalies R (=∂lnVs/∂lnVp), due to temperature difference are consistent with the simulated R values, after an anelastic correction, of MgSiO3 perovskite or pyrolite (a mixture of MgO and MgSiO3 perovskite). Both P and S wave velocity anomalies at the top of the lower mantle correspond to the cold temperature anomalies of 120 K for the cold slabs in which MgSiO3 perovskite is dominant. The magnitude of the P wave velocity anomaly observed, after the anelastic correction, at the core-mantle boundary corresponds to about +270 K. The large S wave velocity anomalies at the core-mantle boundary may be accounted for partial melting and/or the chemical heterogeneity due to relatively high iron contents and the temperature anomaly in this region.