[S-IT22] [EE] 核-マントルの相互作用と共進化

[SIT22-19] Effects of Fe and Al incorporations on MgSiO₃ postperovskite phase boundary

★招待講演

*Xianlong Wang^1,2、Taku Tsuchiya^3,4、Zhi Zeng^1,2 (1.Institute of Solid State Physics, Chinese Academy of Sciences、2.University of Science and Technology of China、3.Geodynamics Research Center, Ehime University、4.Earth-Life Science Institute, Tokyo Institute of Technology)

キーワード：First-principles method, internally consistent LSDA+U, MgSiO3, postperovskite

MgSiO₃ bridgmanite (Br) will undergoes a post-perovskite (PPv) phase transition[1,2,3] in the pressure (P) and temperature (T) conditions corresponding to the Earth’s D” layer. Therefore, The phase change is recognized as the key for understanding the seismological observations in the D” layer. However, to date, it is still a challenging subject to determine the phase transition boundary preciously in the geophysically relevant Fe and Al-bearing compositions. Based on the first-principles methods combined with the internally consistent LSDA+U method and the lattice dynamics approach, the high-P,T thermodynamics of the MgSiO₃ phases are directly calculated with incorporation of 6.25 mol% of Fe²⁺, Fe³⁺Fe³⁺, Fe³⁺Al³⁺, and Al³⁺Al³⁺ [4,5]. Using calculated free energies, we determine the PPv phase boundaries for Fe and Al-bearing compositions. Our results show that at 2500 K, incorporations of Fe³⁺Fe³⁺ and Fe³⁺Al³⁺ span coexisting domains between Br and PPv significantly with lowering the transition pressure, in contrast to the Fe²⁺ and Al³⁺Al³⁺-bearing cases.

References:
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[2] A. Oganov, and S. Ono, Nature 430, 445 (2004).
[3] T. Tsuchiya, J. Tsuchiya, K. Umemoto, and R. M. Wentzcovitch, Earth. Planet. Sci. Lett. 224, 241 (2004).
[4] J. Tsuchiya, and T. Tsuchiya, Proc. Natl. Acad. Sci. USA 105, 19160 (2008).
[5] A. Metsue, and T. Tsuchiya, Geophys. J. Int. 190, 310 (2012).