Thermoelasticity of Fe²⁺‐bearing bridgmanite

Abstract

We present local density approximation augmented by the Hubbard-type correction calculations of high-temperature elastic properties of bridgmanite with composition (Mg (1−x) Fe 2+ x )SiO 3 for 0 ≤ × ≤ 0.125. 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 ∼30 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 and not by the HS to IS crossover. The calculated elastic properties of (Mg 0.875 Fe 2+ 0.125 )SiO 3 along an adiabatic mantle geotherm somewhat overestimate longitudinal velocities but produce densities and shear velocities quite consistent with the Preliminary Reference Earth Model data throughout most of the lower mantle.

Thermodynamic and Elastic Properties of Grossular at High Pressures and High Temperatures: A First‐Principles Study

“…The solid gray and black lines represent PREM (Dziewonski & Anderson, ) and AK135 model (Kennett et al, ), respectively. Data source: CaPv, Ca‐perovskite (Kawai & Tsuchiya, ); MgPv, bridgmanite (Shukla et al, ); Cor, corundum (Wang & Wu, ); Pc, periclase (Wu & Wentzcovitch, ); Gr, grossular (this study); Py, Pyrope (Hu et al, ); Rw, ringwoodite (Núñez Valdez et al, ).…”

“…An isotropic distribution function of strain Grüneisen azimuth angles is assumed in this method, which is true for isotropic material, and the anisotropy of the crystal is considered through the anisotropic pressure dependence of lattice parameters. The method has been applied successfully to many minerals, including MgO (Wu & Wentzcovitch, ), ferropericlase (Wu et al, ), bridgmanite (Shukla et al, ), stishovite and the CaCl 2 ‐type silica (Yang & Wu, ), superhydrous phase B (Yang et al, ), ringwoodite (Núñez Valdez et al, ), olivine and wadsleyite (Núñez Valdez et al, ), pyrope (Hu et al, ), Orthoenstatite (Qian et al, ), diopside (Zou et al, ), and Corundum (Wang & Wu, ).…”

Elasticity of superhydrous phase B at the mantle temperatures and pressures: Implications for 800 km discontinuity and water flow into the lower mantle

“…(a) Compressional wave V p , (b) shear wave V s , and (c) densities of ShyB compared to those of Ak135 model [ Kennett et al ., ] and main phases in the lower transition zone and lower mantle along a slab geotherm (see Figure ) 500 K lower than the normal mantle geotherm. Iron‐free ringwoodite (Rw) [ Núñez Valdez et al ., ], iron‐bearing ringwoodite (Fe‐Rw, Mg 1.75 Fe 0.25 SiO 4 ) [ Núñez Valdez et al ., ], hydrous 1% ringwoodite (hy‐Rw) [ Mao et al ., ], iron‐free bridgmanite (Pv) [ Shukla et al ., ], and periclase (Pc) [ Wu and Wentzcovitch , ].…”

Thermoelasticity of Iron‐ and Aluminum‐Bearing MgSiO3 Postperovskite

“…On the other hand, the aggregate elastic moduli, K , and G are quite indifferent to the atomic configuration (Nunez‐Valdez et al, ). The semianalytical method (Wu & Wentzcovitch, ) used here has been previously applied successfully for Al‐ and Fe‐bearing bridgmanite (Shukla, Wu, et al, ; Shukla, Cococcioni, et al, ) and other minerals (Nunez‐Valdez et al, , ; Wu & Wentzcovitch, ; Yang & Wu, ).…”