Behavior of iron in (Mg,Fe)SiO_3 post-perovskite assemblages at Mbar pressures

Abstract

The electronic environment of the iron sites in post-perovskite (PPv) structured (^(57)Fe,Mg)SiO_3 has been measured in-situ at 1.12 and 1.19 Mbar at room temperature using ^(57)Fe synchrotron Mössbauer spectroscopy. Evaluation of the time spectra reveals two distinct iron sites, which are well distinguished by their hyperfine fields. The dominant site is consistent with an Fe^(3+)-like site in a high spin state. The second site is characterized by a small negative isomer shift with respect to α-iron and no quadrupole splitting, consistent with a metallic iron phase. Combined with SEM/EDS analyses of the quenched assemblage, our results are consistent with the presence of a metallic iron phase co-existing with a ferric-rich PPv. Such a reaction pathway may aid in our understanding of the chemical evolution of Earth's core-mantle-boundary region.