Thermoelasticity of Silicate Perovskite and Magnesiow�stite and Stratification of the Earth's Mantle

Analyses of x-ray-diffraction measurements on (Mg,Fe)SiO3 perovskite and (Mg,Fe)O magnesiow�stite at simultaneous high temperature and pressure are used to determine pressure-volume-temperature equations of state and thermoelastic properties of these lower mantle minerals. Detailed comparison with the seismically observed density and bulk sound velocity profiles of the lower mantle does not support models of this region that assume compositions identical to that of the upper mantle. The data are consistent with lower mantle compositions consisting of nearly pure perovskite (>85 percent), which would indicate that the Earth's mantle is compositionally, and by implication, dynamically stratified.

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