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

Abstract

The Fe2+ -Mg distribution coefficients (KD) between perovskite/postperovskite and ferropericlase were determined in a (N4g0.9Fe0.1)2SiO4 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 KD 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 KD 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. Copyright 2008 by the American Geophysical Union.