Valence/Spin States of Iron in Peridotite Glass to Megabar Pressure Implications for Dense Iron-Rich Silicate Melt at the Bottom of the Mantle

We have conducted high-pressure electrical conductivity and M & ouml;ssbauer spectroscopic measurements of peridotite glass as an analog of silicate melts. We observed the shoulder feature in the M & ouml;ssbauer spectra above 60 GPa due to the emergence of the new Fe2+ component, which could be associated with the change of the iron partitioning coefficient between solid and melt observed in previous melting experiments. The change in the trend of the electrical conductivity profile has been observed at around similar to 83 GPa, suggesting the increase of the relative abundance of the new component. The pressure dependence of hyperfine parameters indicates the spin transitions of both Fe2+ and Fe3+ occur above 100 GPa, which is likely related to the structural change of the glass. Our results suggest that the spin state changes of iron lead to further densification of the silicate melts at the bottom of the mantle.