Determination of post-perovskite phase transition boundary up to 4400 K and implications for thermal structure in D″ layer

We have determined the post-perovskite phase transition boundary in MgSiO₃ in a wide temperature range from 1640 to 4380 K at 119-171 GPa on the basis of synchrotron X-ray diffraction measurements in-situ at high-pressure and -temperature in a laser-heated diamond-anvil cell (LHDAC). The results show a considerably high positive Clapeyron slope of + 13.3 ± 1.0 MPa/K and a transition temperature of about 3520 ± 70 K at the core-mantle boundary (CMB) pressure. The thermal structure in D″ layer can be tightly constrained from precisely determined post-perovskite phase transition boundary and the depths of paired seismic discontinuities. These suggest that temperature at the CMB may be around 3700 K, somewhat lower than previously thought. A minimum bound on the global heat flow from the core is estimated to be 6.6 ± 0.5 TW.