Thermoelasticity of Fe$^{3+}$- and Al-bearing bridgmanite

Gaurav Shukla; Matteo Cococcioni; Renata M. Wentzcovitch

paper

Thermoelasticity of Fe $^{3 +}$ - and Al-bearing bridgmanite

arXiv:1603.08899

Abstract

We report \textit{ab initio} (LDA + U $_{sc}$ ) calculations of thermoelastic properties of ferric iron (Fe $^{3 +}$ )- and aluminum (Al)-bearing bridgmanite (MgSiO $_{3}$ perovskite), the main Earth forming phase, at relevant pressure and temperature conditions and compositions. Three coupled substitutions, namely, [Al] $_{M g}$ -[Al] $_{S i}$ , [Fe $^{3 +}$ ] $_{M g}$ -[Fe $^{3 +}$ ] $_{S i}$ , and [Fe $^{3 +}$ ] $_{M g}$ -[Al] $_{S i}$ have been investigated. Aggregate elastic moduli and sound velocities are successfully compared with limited experimental data available. In the case of the [Fe $^{3 +}$ ] $_{M g}$ -[Fe $^{3 +}$ ] $_{S i}$ substitution, the high-spin (S=5/2) to low-spin (S=1/2) crossover in [Fe $^{3 +}$ ] $_{S i}$ induces a volume collapse and elastic anomalies across the transition region. However, the associated anomalies should disappear in the presence of aluminum in the most favorable substitution, i.e., [Fe $^{3 +}$ ] $_{M g}$ -[Al] $_{S i}$ . Calculated elastic properties along a lower mantle model geotherm suggest that the elastic behavior of bridgmanite with simultaneous substitution of Fe $_{2}$ O $_{3}$ and Al $_{2}$ O $_{3}$ in equal proportions or with Al $_{2}$ O $_{3}$ in excess should be similar to that of (Mg,Fe $^{2 +}$ )SiO $_{3}$ bridgmanite. Excess Fe $_{2}$ O $_{3}$ should produce elastic anomalies though.

arXiv commentUnder review with Geophysical Research Letters

Thermoelasticity of Fe3+- and Al-bearing bridgmanite

Abstract

References in corpus (7)

Thermoelasticity of Fe $^{3 +}$ - and Al-bearing bridgmanite