Mineral physics constraints on the chemical composition and temperature of the Earth's mantle

Numerical mineral physics modeling is used in seven studies to constrain the composition and dynamics of the Earth's mantle. First, using updated, published experimental data, I evaluate two competing mineralogical models for the composition of the mantle by calculating and comparing one dimensional profiles of density (ρ) and bulk sound velocity (V _&phis;) against seismologically inferred profiles. Second, to further test the predicted properties of the uniform composition, pyrolite model, the mineral physics calculations are extended to predict one dimensional profiles of shear (V_S) and compression (V _P) velocity across the upper mantle and transition zone. Third, I estimate a high temperature value for $6m/6TMg-PvP$ of Mg-perovskite via constrained adiabatic decompression of the lower mantle PREM seismic properties. A simplified pyrolite lower mantle mineralogy of magnesiowüstite and Mg-Fe perovskite is used to provide apriori constraints for some of the unknown high temperature decompressed properties thereby restricting the possible parameter space for the decompressed hot shear modulus (μ₀). Fourth, adopting this estimate of $6m/6TMg-PvP$, and estimating $6m/6TCa-PvP$ via a high temperature thermodynamic approximation, I then iteratively adjust the unmeasured pressure derivative, $6m/6TMg-PvP$, under the first order assumption $6m/6TMg-PvP$ = $6m/6TCa-PvP$, until predicted one dimensional profiles of V_S and V_P for a pyrolite mineralogy match the seismic profiles across the lower mantle. Fifth, I incorporate the recent experimental and theoretical values for Mg-perovskite and compare these with the inferences deduced in the previous chapters. Sixth, I utilize the pyrolite V _S and V_P profiles to evaluate the ratio of relative V_S and V_P velocity heterogeneity in the mantle via the parameter (∂lnV _S/∂lnV_P)_P. Seventh, I estimate new extremal bounds for the lateral temperature anomalies in the mantle using the pyrolite mineral physics model of V_S and V_P. I conclude that away from chemical and thermal boundary layers, the lateral seismic anomalies resolved in tomographic studies are largely thermal in origin and consequently, the dominant force driving mantle convection is indeed thermal buoyancy. (Abstract shortened by UMI.)...