Thermal convection thinning of the North China Craton: Numerical simulation

We used two-dimensional numerical simulations to investigate small-scale convection in the upper mantle-lithosphere system with depthand temperature-dependent viscosity. Our aim was to examine the mechanism of craton thinning by thermal convection. The model domain is 700 km deep and 700 km wide with a resolution of 71×71 nodes and 160000 markers. The velocity boundary conditions are free-slip along all the boundaries. A thermal insulation condition was applied at the two side walls, with constant temperatures for the top and bottom boundaries. We assumed an initial temperature of 273 K at the upper boundary and 1673 K at the lower boundary, and 1573 K at the bottom of the lithosphere (200 km depth) for the thick, cold, and stable North China Craton (NCC). We calculated the thermal evolution in the upper mantle when the temperature at its bottom is raised because of lower mantle convection or plumes. The temperature at the bottom of the upper mantle was set at 1773, 1873, 1973, and 2073 K for different models to study the temperature effect on the lithospheric thinning processes. Our end-member calculations show that with the bottom boundary raising the lithosphere can be thinned from a depth of 200 km to a depth of between 100 and 126.25 km. The thinning rates are at mm/y order of magnitude, and the thinning timescale is about 10 Ma.