Effect of post-perovskite rheology on the thermal evolution of the Earth

Abstract Secular cooling of the Earth mantle is a complex process affected by many factors. Here we present the results of a modelling study focused on efficiency of cooling in the presence of rheologically distinct post-perovskite. We evaluate combined effects of variable thermal expansivity and diffusivity, initial thermal condition and heat source model and concentrate on the effects of rheologically weak post-perovskite. Cooling of the core is included in the model—core is assumed to be an isothermal heat reservoir with temperature controlled by heat flux through core–mantle boundary. Our 2D axisymmetric convection model has pressure, temperature and phase dependent viscosity and includes the effects of an endothermic phase transition at 660 km depth and an exothermic perovskite-post-perovskite phase transition in the lowermost mantle. In agreement with previous studies we conclude that depth-dependent material parameters tend to delay secular cooling. Presence of the weak post-perovskite on the other hand significantly enhances core cooling and its effect on core temperature is opposite and comparable in magnitude.