Mechanical and thermal effects of floating continents on the global mantle convection

Numerical models are presented that simulate mantle convection coupled with superimposed continents. The continents and main islands are modelled as thin rigid spherical caps with non-slip boundary conditions and continuity conditions for temperature and heat flux at their bottom. Additional repulsive forces prevent overlap of the continents in the case of their collision. The initial temperature distribution in the mantle is calculated based on seismic tomography data. The evolving mantle model implies 10% basal and 90% internal heating and uniform viscosity. Mechanical coupling leads to near horizontal convection currents under continents and consequently to a noticeable decrease of the mantle temperature under them in spite of the thermal blanket effect. The modelling results show that a long-term evolution of the free convection model and of the model with implemented continents leads to principally different structures. Several common stages of the continental evolution are revealed. Back-arc basins at the active continental margins are closed at the first stage. In the next stage of the modelled evolution the convection pattern is reorganized and the main downwellings start to move to the south pulling the continents, which tend to assemble a new super-continent around Antarctica. Due to the repulsive forces the continents rotate and adjust to each other.