Partitioning of iron between perovskite/postperovskite and ferropericlase in the lower mantle

The Fe2+-Mg distribution coefficients (K-D) between perovskite/postperovskite and ferropericlase were determined in a (Mg0.9Fe0.1)(2)SiO4 bulk composition. High-pressure and high-temperature experiments were carried out between 36 and 128 GPa and 1760-2170 K in a laser-heated diamond anvil cell (LHDAC). Chemical analyses were made on recovered samples with transmission electron microscope (TEM) and field-emission-type scanning electron microscope (FE-SEM). All the samples exhibited a strong heterogeneity in iron content caused by relatively large temperature gradient during laser-heating, being depleted at the center of the hot spot and enriched at the margin. The K-D values measured from coexisting perovskite/postperovskite and ferropericlase showed apparently very large variation in each sample, which could be the source of considerable discrepancy among previous measurements of K-D using the LHDAC techniques. Nevertheless, the data obtained from a specific portion of the sample that retained the original bulk composition may represent the equilibrium partitioning. Present results demonstrate that the iron partitioning between perovskite/postperovskite and ferropericlase changes little at a given temperature throughout the lower mantle pressures. Both electronic transition of iron and postperovskite phase transition have small effects on iron partitioning.