Mantle dynamics with the post-perovskite phase change: Numerical simulations with the latest constraints from mineral physics

We present results of numerical simulations of mantle convection with the perovskite-postperovskite phase change. Using the extended Boussinesq approximation for a fluid with temperature and pressure dependent viscosity, we perform an extensive sensitivity study of characteristic post-perovskite parameters and investigate their effects on the convective planform, heat transport, temperature and viscosity profiles. Since post-perovskite is expected to have both a large electrical (Ohta et al., 2008) and thermal (Hofmeister, 2007, Dong and Li, 2009) conductivity, we assume that the transition from perovskite to this phase is accompanied by both a reduction in viscosity by 1 to 2 orders in magnitude and by an increase in thermal conductivity by a factor of 2. Furthermore, we investigate the combined effects of decreasing pressure-dependent thermal expansivity, by considering the most recent finding by T. Katsura and colleagues (2009), and steeply increasing thermal conductivity (Hofmeister, 2009, Dong and Li, 2009). In general, the presence of post-perovskite destabilizes the D" region, focussing the heat-flux peaks and increasing the average mantle temperature and the temporal and spatial frequency of upwellings. In particular, using depth dependent thermal expansivity, the latest thermal conductivity models and no post-perovskite results in a very sluggish convective regime in the lower mantle with few and large sized up- and downwellings. Taking into account post-perovskite helps to reduce the viscosity of the lower mantle and to create a more realistic dynamical slab regime and stable narrow plumes rising from the bottom thermal boundary layer.