Three-dimensional mantle convection simulations with a low-viscosity asthenosphere and the relationship between heat flow and the horizontal length scale of convection

Numerical mantle convection simulations show that depth-dependent viscosity can increase the flow wavelength. A recent analysis demonstrates that flow channelization into a low-viscosity region lowers lateral dissipation. This allows long wavelength flow to more efficiently cool the interior mantle. We present three-dimensional, mixed heating mantle convection simulations with a thin low-viscosity channel for a range of aspect ratios to test the implications of the theoretical analysis. For reasonable viscosity contrasts between lithosphere, asthenosphere and bulk mantle we find that very large aspect ratios can develop. Velocity profiles quantify the degree of channelization for variable aspect ratios. Internal temperatures are found to decrease with increasing aspect ratio and both surface heat flux and velocity are found to increase with aspect ratio. Our results are consistent with the idea that the asthenosphere channels lateral mantle flow which, in turn, stabilizes long wavelength convection cells and makes long wavelength flow energetically favorable.