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The effect of temperature on the seismic anisotropy of the perovskite and post-perovskite polymorphs of MgSiO3

2005; Elsevier BV; Volume: 230; Issue: 1-2 Linguagem: Inglês

10.1016/j.epsl.2004.11.021

1385-013X

Stephen Stackhouse, John P. Brodholt, James Wookey, J. M. Kendall, G. D. Price,

Geological and Geochemical Analysis

Using elastic constants determined by ab initio molecular dynamics over a range of temperatures, we show that the seismic anisotropy of MgSiO3 perovskite is significantly temperature dependent. At 90 GPa, the direction of greatest shear wave splitting changes from [001] at 0 K to [010] at 3500 K. In addition, there is no shear wave splitting in the [100] direction at 0 K, but a significant amount of splitting is exhibited at 3500 K. We have also calculated the first set of high-temperature elastic constants of the new post-perovskite phase by ab initio molecular dynamics methods. We find that, in contrast to MgSiO3 perovskite, temperature has little effect on the acoustic anisotropy of this phase. We determine ∂ln VS/∂ln VP for the post-perovskite phase and find it to be very low, about 0.9. This may be an important parameter for mapping out the post-perovskite phase in the lowermost mantle.