High-temperature compression of iron-bearing silicate perovskite and the density model of the lower mantle

The lower mantle chemistry is one of the central issues for understanding the origin and evolution of the solid Earth. Historically, there have been two compositional models for the lower mantle, namely the peridotitic lower mantle with Mg/Si ~ 1.5 and perovskitic mantle with Mg/Si ~1.0. The principal difference in mineralogy between the two models are the modal amounts of (Mg,Fe)SiO3 perovskite and (Mg,Fe)O ferropericlase. The density profile of those minerals based on laboratory measurements allows us to test the two compositional models by the comparison with the seismological density model. The pressure (P)- volume (V)- temperature (T) equations of state (EoS) for those minerals in the Mg-end member have been extensively studied up to the P-T conditions of the core-mantle boundary. However, only a few studies have reported thermal EoS for iron-bearing phases. In addition, the experimental P-T ranges for those works do not cover the entire lower mantle. Therefore, in order collect the unit-cell volume data and examine the effect of iron on the compression behavior, we conducted simultaneous high-P-T in-situ X-ray diffraction (XRD) measurements of (Mg0.9Fe0.1)SiO3 perovskite under lower mantle conditions. High-P-T conditions were generated in a laser-heated diamond anvil cell with a membrane system. The membrane system enables us to compress the sample during laser heating, so that we collect the unit-cell volume data of the sample efficiently. In addition, since the membrane system can compress the sample isothermally, the compression behavior is precisely resolved. Angle-dispersive X-ray diffraction spectra were obtained at the station BL10XU of SPring-8. We performed high-temperature compression experiments to the deep lower mantle P-T conditions. We will present the new data of thermal EoS for iron-bearing perovskite and based on it, we discuss the mineralogy of the lower mantle.