Abstract
We investigated temperature dependency of a Clapeyron slope (dP/dT) associated with phase transition at a depth of about 660 km on mode of mantle convection in a 2-D rectangular box numerically, using the extended Boussinesq approximation. We considered models with a negative Clapeyron slope below 1800 ºC, and positive value above the temperature based on recent high P-T experiment. The 410 km phase boundary, temperature and depth dependent viscosity, and heating by adiabatic compression were taken into account in all the models. The results show that mantle overturn comes to take place irregularly, and its frequency increases dramatically with increasing temperature difference between the top and bottom model boundaries for the case with the temperature dependency of dP/dT. This is interpreted as the effect that hot plumes promote mantle convection for positive Clapeyron slope. However, the calculated result does not necessarily show that mantle upwelling triggers mantle overturn. Frictional and internal heating plays a role to increase the frequency as well, but the effect of the temperature difference is not so remarkable.
