The lower mantle is the largest layer of the Earth. Pressures and temperatures there vary from 23 GPa to 135 GPa and ~1,900 K to 4,000 K. Aluminous perovskite, Al-Mg1−xFexSiO3, and ferropericlase, Mg1−xFexO, are the most important phases of the Earth’s lower mantle, comprising ~62 vol% and ~35 vol% of this region, respectively. The remaining consists of CaSiO3-perovskite, according to the pyrolitic compositional model (Ringwood 1982). Silicate perovskite transforms into another polymorph, post-perovskite, at conditions expected to occur near the D″ discontinuity in the...

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