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Thermoelasticity of Fe2+-bearing bridgmanite

Abstract

We present LDA+U calculations of high temperature elastic properties of bridgmanite with composition (Mg(1x)_{(1-x)}Fex2+_{x}^{2+})SiO3_3 for 0x0.1250\le{x}\le0.125. Results of elastic moduli and acoustic velocities for the Mg-end member (x=0) agree very well with the latest high pressure and high temperature experimental measurements. In the iron-bearing system, we focus particularly on the change in thermoelastic parameters across the state change that occurs in ferrous iron above \sim30 GPa, often attributed to a high-spin (HS) to intermediate spin (IS) crossover but explained by first principles calculations as a lateral displacement of substitutional iron in the perovskite cage. We show that the measured effect of this change on the equation of state of this system can be explained by the lateral displacement of substitutional iron, not by the HS to IS crossover. The calculated elastic properties of (Mg0.875_{0.875}Fe0.1252+_{0.125}^{2+})SiO3_3 along an adiabatic mantle geotherm, somewhat overestimate longitudinal velocities but produce densities and shear velocities quite consistent with Preliminary Reference Earth Model data throughout most of the lower mantle.Comment: Accepted for Geophysical Research Letters (DOI: 10.1002/2014GL062888

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