Post‐perovskite phase transition and mineral chemistry in the pyrolitic lowermost mantle

Abstract

Phase relations of a natural mantle composition were determined up to 126 GPa and 2450 K by in‐situ x‐ray diffraction measurements in a laser‐heated diamond‐anvil cell (LHDAC). MgSiO 3 ‐rich perovskite (MgPv) transforms to a post‐perovskite phase (MgPP) at about 113 GPa and 2500 K (400‐km above the core‐mantle boundary) and the lowermost mantle consists of MgPP, (Mg, Fe)O magnesiowüstite (Mw), and CaSiO 3 ‐rich perovskite (CaPv). Chemical analyses on recovered samples using transmission electron microscope (TEM) show that the distribution of iron significantly changes at the post‐perovskite phase transition. A strong enrichment of iron in Mw leads to the unique geophysical and geochemical properties of the lowermost mantle.