Chemical composition of the lower mantle inferred from the equation of state of MgSiO3 perovskite

The chemical composition of the lower mantle is estimated based on the most reliable equation of state for MgSiO3 perovskite, obtained by an in situ X-ray diffraction study up to 29 GPa and 2000 K. The density profile and temperature gradient of various compositions are compared with those of the preliminary reference Earth model (PREM). Assuming that the lower mantle consists of a mixture of (Mg-1-x,Fe-x)SiO3 perovskite and (Mg-1-y,Fe-y)O magnesiowustite, the mixing ratio (in molar ratio), which is in harmony with the PREM, is in the range from 2:1 to 3:1 of perovskite and magnesiowustite when the total iron content. Fe/(Mg + Fe), is about 0.11. If the iron content is higher than this, the amount of magnesiowustite decreases. An iron content less than 0.11 implies too low temperature compared to the geotherm, while if it is 0.15 or more, too high temperature is required.