The equation of state of orthorhombic perovskite in a peridotitic mantle composition to 80 GPa: implications for chemical composition of the lower mantle

In situ X-ray diffraction of orthorhombic perovskite, which is the dominant phase in the Earth’s lower mantle, was carried out on a sample with a KLB-1 peridotite composition up to a pressure of 80 GPa using a laser-heated diamond anvil cell (LHDAC) with X-rays from a synchrotron radiation source. At each pressure increment, the sample was heated using a YAG laser to relax the deviatoric stress in the sample. The bulk modulus of the orthorhombic perovskite, which contained FeO, Al2O3, TiO2, CaO, and Na2O, was nearly equal to, or slightly larger than that of pure MgSiO3 perovskite. The density of the KLB-1 peridotite at the top of the lower mantle estimated using thermoelastic parameters, is in good agreement with a density profile (PREM) determined from seismic observations. The KLB-1 peridotite composition is, therefore, consistent with the bulk composition of the upper part of the lower mantle.