Thermal convection in the continental upper mantle and its effect in geophysical fields

Results of a numerical modeling of thermal convection in the upper mantle of the continents are discussed. Geological, geophysical, and isotopic data are given in support of representation of lithosphere as a rigid conductive layer of variable thickness which is not destroyed by mantle processes. The thermal convection consists of an ascending flow beneath thick (to 200 km) lithosphere of an ancient platform and a descending Flow beneath thin (120-150 km) lithosphere of younger fold belts surrounding the platform. Methods for calculation of the geophysical characteristics of the convection - surface relief and gravitational field - are discussed. It is shown that agreement between the observed and modeled characteristics is achieved only by regarding lithosphere as a rigid layer.