3 REGIMES OF MANTLE CONVECTION WITH NON-NEWTONIAN VISCOSITY AND STAGNANT LID CONVECTION ON THE TERRESTRIAL PLANETS

Numerical simulations of convection with strongly temperature-dependen t viscosity suggest that non-Newtonian viscosity convection (dislocati on creep) passes through three convective regimes similar to those obs erved for Newtonian viscosity convection (diffusion creep): the small viscosity contrast regime, the transitional regime and the stagnant li d regime. For realistic viscosity contrasts, mantle convection is in t he stagnant lid regime characterized by formation of a very viscous, s lowly creeping lid on top of an actively convecting mantle. This expla ins the tectonic style observed on the terrestrial planets and the Moo n. On the other hand, this eliminates the possibility that the plates on Earth could be mobile due to non-Newtonian viscosity. The nature of the mobility of lithospheric plates on Earth has yet to be explained.