Thermoelasticity of Al3+- and Fe3+-bearing bridgemanite

Abstract:

We present quasi-harmonic LDA+U calculations of thermoelastic properties of Fe³⁺- and Al³⁺-bearing bridgemanite (MgSiO₃), the main phase of the Earth’s lower mantle, at relevant P,T conditions and compositions. Four charge-coupled substitutions, namely, Al³⁺-Al³⁺, Fe³⁺-Fe³⁺, Fe³⁺-Al³⁺, and Al³⁺-Fe³⁺have been studied. Aggregate elastic moduli and sound velocities are compared with available experimental measurements. In the case of the Fe³⁺-Fe³⁺ substitution, the effect of pressure induced high-spin (HS) to low-spin (LS) crossover in the B-site iron has been investigated in great detail. Using these results, we analyze the possible influence of Al and Fe on lower mantle velocity heterogeneities.