Experimental constraints on the temperature profile in the lower mantle

A thermal model of the pyrolite mantle composition has been investigated using recent experimental data. The geotherm of the lower mantle can be constrained by several phase transitions: olivine-wadsleyite, post-spinel, post-perovskite, and cubic–orthorhombic Ca-perovskite. However, the spin transition of ferropericlase cannot be used to constrain the geotherm, because the uncertainty of the spin transition pressure is significantly high in both previous experimental and previous theoretical studies. By comparing the depth of seismic discontinuities with transition pressure, plausible temperatures at depths of 660 and 2700 km were estimated to be 1850 and 2600 K, respectively. The average adiabatic temperature gradient in the lower mantle was 0.367 K/km. The temperature rapidly increased at the base of the lower mantle because the super-adiabatic gradient controls the temperature profile at the thermal boundary layer. The temperature at the core–mantle boundary was estimated to be 4000 K. The estimated geotherm is in good agreement with the lower limit temperature estimated from the Ca-perovskite phase transition between the cubic and orthorhombic symmetries, and the upper limit temperature estimated using the solidus of the pyrolite composition.