CENOZOIC PLATE DRIVING FORCES

Past studies of plate driving forces have concluded that the forces du e to subducted slabs in the upper mantle and those due to the thickeni ng of the oceanic lithosphere are the principal driving forces. We ree xamine the balance of driving forces for the present-day and extend ou r analysis through the Cenozoic, using an analytical torque balance me thod which accounts for interactions between plates via viscous coupli ng to the induced mantle flow, We use an evolving mantle density heter ogeneity field based on the last 200 Myr. of subduction to drive plate motions, an approach which has proven successful in predicting the pr esent-day mantle heterogeneity field. We find that for plausible upper mantle viscosities the forces due to subducted slabs in the Cenozoic and Mesozoic account for in excess of 90% of plate driving forces and those due to lithospheric thickening for less than 10%.