PLATE GENERATION IN A SIMPLE MODEL OF LITHOSPHERE-MANTLE FLOW WITH DYNAMIC SELF-LUBRICATION

Abstract

One of the more enigmatic features of the Earth's style of mantle convection is plate tectonics itself, in particular the existence of strike-slip, or toroidal, motion. Toroidal motion is uncharacteristic of basic thermal convection, but necessarily forms through the interaction of convective flow and nonlinear rheological mechanisms. Recent studies have implied that the empirically determined power-law rheologies of mantle silicates are not sufficient to generate the requisite toroidal motion. A simple source-sink model of mantle or lithospheric flow shows that dynamic self-lubrication, which arises through the coupling of viscous heating and temperature-dependent viscosity, is highly successful at generating strike-slip motion. In particular, as the viscosity of the fluid system becomes more temperature dependent, the toroidal flow field makes an abrupt transition from a state of weak, unplate-like motion to a state with intense and extremely focused structure. In essence, the fluid dynamical model develops strike-slip faults.