First principles thermoelasticity of MgSiO3-perovskite: Consequences for the inferred properties of the lower mantle

Bijaya B. Karki, Renata M. Wentzcovitch, Stefano De Gironcoli, Stefano Baroni

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Some key thermoelastic properties of MgSiO3- perovskite (pv) have been determined at lower mantle (LM) pressures and temperatures using the quasi-harmonic approximation in conjunction with first principles phonon dispersions. The adiabatic bulk moduli (KS) of pv and of an assemblage of 80 vol% pv and 20 vol% MgO were obtained along the thermodynamically inferred adiabat and compared with the seismic counterpart given by the preliminary reference Earth model (KPREM). The discrepancy between calculated KS's and KPREM in the deep LM suggests a super-adiabatic gradient, or subtle changes of composition, or phase, or all beginning at about 1200 km. The Anderson Grüneisen parameter, δs = (∂lnKs/∂lnρ)P, was predicted to decrease rapidly with a depth (from 2.7 to 1.2 across the LM) supporting the thermal origin for the lateral heterogeneities throughout most of the LM.

Original languageEnglish (US)
Pages (from-to)2699-2702
Number of pages4
JournalGeophysical Research Letters
Issue number14
StatePublished - Jul 15 2001

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