Phase transitions in MgSiO3 post-perovskite in super-Earth mantles

1,2,3Koichiro Umemoto, 4,5,6Renata M. Wentzcovitch, 3,7Shunqing Wu, 3Min Ji, 3Cai-Zhuang Wang, 3Kai-Ming Ho
Earth and Planetary Science Letters 478, 40-45 Link to Article [https://doi.org/10.1016/j.epsl.2017.08.032]
1Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
2Department of Earth Sciences, University of Minnesota, 310 Pillsbury drive SE, Minneapolis, MN 55455, USA
3Ames Laboratory, US DOE and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
4Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
5Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, USA
6Lamont–Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
7Department of Physics, Xiamen University, Xiamen 361005, China
Copyright Elsevier

The highest pressure form of the major Earth-forming mantle silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed the problem of mantle composition, particularly major element abundances usually expressed in terms of three main variables, the Mg/Si and Fe/Si ratios and the Mg#, as in the Earth. Here we show that the critical compositional parameter, the Mg/Si ratio, whose value in the Earth’s mantle is still debated, is a vital ingredient for modeling phase transitions and internal structure of super-Earth mantles. Specifically, we have identified new sequences of phase transformations, including new recombination reactions that depend decisively on this ratio. This is a new level of complexity that has not been previously addressed, but proves essential for modeling the nature and number of internal layers in these rocky mantles.

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