Constraints on lower mantle composition from molecular dynamics simulations Of MgSiO3 perovskite

We have carried out molecular dynamics simulations Of MgSiO3 perovskite (pv) in order to determine its equation of state and elastic parameters under pressure and temperature conditions of the Earth's lower mantle. Combining this information with density and elastic constants for (Mg,Fe)O magnesiowustite (mw) and including the effects of iron on the density of perovskite, we investigated possible compositional models for the lower mantle by calculating seismic velocities and densities as functions of depth and comparing them to the globally averaged seismological models ak135-f and PREM. The calculations were done along several possible geothermal gradients, both adiabatic and non-adiabatic, and for a range of Mg-Fe partitioning coeffcients, K-Fe-Mg(pv-mv) = 0.10-0.35. Our results indicate that the most probable compositional models for the lower mantle are pyrolitic, with X-Mg approximate to 0.87 and X-pv approximate to 0.54. For increasing temperatures at the top of the lower mantle, the best fitting models increase slightly in both iron and silica content. (C) 2002 Elsevier Science B.V. All rights reserved.