SELF-MODULATION OF THERMAL CONVECTION WAVES IN THE EARTH'S MANTLE

Abstract

The large-scale thermal convection that causes lithospheric plates to move generates in the upper part of each mantle cell a thermal boundary layer that travels at a constant speed without distortion. There is a strong vertical temperature gradient in their layer which makes it convectively unstable. To describe 'secondary' small-scale convection in the boundary layer which induces finite deformations in it, the author uses a linear rheological model with memory, corresponding to the case of unsteady-state creep of the mantle. Linear analysis of convective instability, in which the nonlinear terms are discarded from heat balance, leads to a solution in the form of convective waves. Conditions for the self-modulation of thermal convection waves are then determined and studied, and results are discussed.