[S-IT20] Structure and Dynamics of Earth and Planetary Mantles

[SIT20-10] Low-pressure analogs of MgSiO₃ post-perovskite at ultrahigh pressures by first principles

*Koichiro Umemoto¹, Renata Wentzcovitch² (1.Earth-Life Science Institute, Tokyo Institute of Technology, 2.Department of Applied Physics and Applied Mathematics, Department of Earth and Environmental Sciences, Lamont Doherty Earth Observatory, Columbia University, USA)

Keywords:Post-post-perovskite transitions, first principles, deep interiors of terrestrial exoplanets

MgSiO₃ post-perovskite (Mg-PPV) is the final form of this silicate in the Earth’s mantle. However, the fate of Mg-PPV in the mantle of terrestrial exoplanets, where pressures and temperatures are much higher than those on Earth, is still an open question. Knowledge of such transitions will be fundamental for numerical simulations of mantles in terrestrial exoplanets. Previously, by first principles, we predicted a complex series of phase transitions involving dissociation (MgSiO₃ -> Mg₂SiO₄ + MgSi₂O₅ -> Mg₂SiO₄ + SiO₂ -> MgO + SiO₂) and recombination (MgO + MgSiO₃ -> Mg₂SiO₄ or SiO₂ + MgSiO₃ -> MgSi₂O₅) reactions among silicates and elementary oxides. These transitions also depend on the chemical compositions of planetary mantles [1,2] and occur at very high pressure (above ~0.5 TPa), which makes experimental validation rather difficult. Here, we search for these low-pressure analogs using first principles calculations. We hope the present study will facilitate experimental validation and encourage researchers of numerical simulations of mantles in terrestrial exoplanets to take dissociations and recombinations of Mg-PPV into account.



[1] S. Q. Wu, M. Ji, C. Z. Wang, M. C. Nguyen, X. Zhao, K. Umemoto, R. M. Wentzcovitch, K. M. Ho, J. Phys. Condensed Matter, 26, 035402 (2014).

[2] K. Umemoto, R. M. Wentzcovitch, S. Q. Wu, M. Ji, C. Z. Wang, and K. M. Ho, Earth Planet. Sci. Lett. 478, 40 (2017).