Effects of sub-lithospheric small-scale convection with a Newtonian rheology on the seafloor topography and heat flux

Seafloor topography and heat flux show clear dependence on the age of seafloor. A half-space cooling (HSC) model can reproduce seafloor topography and heat flux data for younger seafloor, but for older seafloor the observations show reduced variations with the age in comparison with the HSC model predictions. The deviation was attributed to the sub-lithospheric small-scale (SSC) convection first by Par- sons and McKenzie (1978). While there is little doubt that the SSC can enhance heat flux at relatively old seafloor, ques- tions were raised as to whether or not the SSC can actually lead to a reduced topography. In this study, the effects of SSC on seafloor topography and heat flux are investigated by formulating a 2-D thermal convection model that is parallel to plate motion. Instead of using closed boundary conditions, which will bring large pressure effects because of return flow, a flow through boundary condition is adopted. The results show that although the SSC enhances the surface heat flux, it has little effects on topography for the fluids with a more realistic rheology. The reason for this is that the SSC trans- ports the heat from the bottom to the top and cools down the whole fluids, and with the existence of a stagnant lid, the whole effects on topography are negligible.