High-temperature compression experiments of CaSiO3 perovskite to lowermost mantle conditions and its thermal equation of state

In order to examine pressure-volume-temperature (P-V-T) relations for CaSiO3 perovskite (Ca-perovskite), high-temperature compression experiments with in situ X-ray diffraction were performed in a laser-heated diamond anvil cell (DAC) to 127 GPa and 2,300 K. We also employed an external heating system in the DAC in order to obtain P-V data at a moderate temperature of 700 K up to 113 GPa, which is the reference temperature for constructing an equation of state. The P-V data at 700 K were fitted to the second-order Birch-Murnaghan equation of state, yielding K (700,1bar) = 207 +/- A 4 GPa and V (700,1bar) = 46.5 +/- A 0.1 (3). Thermal pressure terms were evaluated in the framework of the Mie-Gruneisen-Debye model, yielding gamma (700,1bar) = 2.7 +/- A 0.3, q (700,1bar) = 1.2 +/- A 0.8, and theta (700,1bar) = 1,300 +/- A 500 K. A thermodynamic thermal pressure model was also employed, yielding alpha(700,1bar) = 5.7 +/- A 0.5 x 10(-5)/K and (a,K/a,T) (V) = -0.010 +/- A 0.004 GPa/K. Computed densities along a lower mantle geotherm demonstrate that Ca-perovskite is denser than the surrounding lower mantle, suggesting that Ca-perovskite-rich rocks do not rise up through the lower mantle. One of such rocks might be a residue of partial melting of subducted mid-oceanic ridge basalt (MORB) at the base of the mantle. Since the partial melt is FeO-rich and therefore denser than the mantle, all the components of subducted MORB may not return to shallow levels.