Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

Both seismic observations of dense low shear velocity regions and models magma ocean crystallization mantle dynamics support enrichment iron in Earth’s lowermost mantle. Physical properties iron-rich lower heterogeneities the modern Earth depend on distribution between coexisting phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO3 bridgmanite, post-perovskite. The partitioning these was investigated synthetic ferrous-iron-rich olivine compositions (Mg0.55Fe0.45)2SiO4 (Mg0.28Fe0.72)2SiO4 at conditions ranging from 33–128 GPa 1900–3000 K laser-heated diamond anvil cell. resulting phase assemblages were characterized by a combination situ X-ray diffraction ex transmission electron microscopy. exchange coefficient bridgmanite magnesiowüstite decreases with pressure bulk Fe# increases temperature. Thermodynamic modeling determines that incorporation are explained well excess volume associated Mg-Fe exchange. Partitioning results used to model densities as function pressure, FeO-content SiO2-content. Unlike average compositions, exhibit negative dependence density SiO2-content all depths, an important finding for interpretation deep structures.