TEMPERATURE-DEPENDENT NEWTONIAN AND NON-NEWTONIAN CONVECTION - IMPLICATIONS FOR LITHOSPHERIC PROCESSES

Convection studies of temperature-dependent Newtonian and non-Newtonian rheology in aspect-ratio seven boxes have been carried out for volume averaged Rayleigh numbers between O(10(5)) and O(10(7)). Large lateral viscosity variations, O(10(4)) are found for non-Newtonian cases with total temperature-dependent viscosity variations up to 250. Flow structures for both rheologies are distinguished by large-scale circulations with relatively stable descending limbs. Much larger hot thermal anomalies are found near the surface for non-Newtonian rheology. Lithospheric thinning is facilitated by non-Newtonian rheology because of stress-softening and the lubrication of the descending limbs by hot diapirs.