Elasticity of ferropericlase at lower mantle conditions

Zhongqing Wu, University of Science and Technology of China, Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Space Sciences, Hefei, China, João F Justo, Universidade de São Paulo, São Paulo, Brazil and Renata Wentzcovitch, University of Minnesota Twin Cities, Minneapolis, MN, United States
Abstract:
Clarification of the effect of the iron spin change on properties of Fp is important to address the relative abundance of Fp in the lower mantle. However, recent reports to this question show completely different conclusions. The calculated density of a pyrolite aggregate with spin crossover-related change in iron partitioning up to 45 GPa compared well with the density in PREM [1]. On the other hand, Murakami et al’s analysis of VS in aggregates with variable amounts of Fp concluded the opposite - the lower mantle is more perovskitic than pyrolitic [2].

We investigated thermoelasticity of Fp with first principles DFT+U calculations. The calculated thermoelasticity are in good consitence with the available experimental data on samples with various iron concentrations. The results can well explain discrepancy on softening of the shear modulus of Fp among different experiments[3,4]. We predict velocities of Fp at lower mantle conditions and suggest that pyrolite is a reasonable compositional model for the lower mantle. Our results show the importance of constraining the elastic properties of minerals without extrapolations for analyses of the thermochemical state of this region[5].

[1] Irifune et al., Science 327, 193 (2010).

[2] Murakami et al., Nature 485, 90 (2012).

[3] Crowhurst et al., Science 319, 451 (2008).

[4] Marquardt et al., Science 324, 224 (2009).

[5]Wu et al., Phys. Rev. Lett. 110. 228501 (2013)

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