COUPLING OF SOUTH-AMERICAN AND AFRICAN PLATE MOTION AND PLATE DEFORMATION

Although the African Plate's northeastward absolute motion slowed abru ptly 30 million years ago, the South Atlantic's spreading velocity has remained roughly constant over the past 80 million years, thus requir ing a simultaneous westward acceleration of the South American Plate, This plate velocity correlation occurs because the two plates are coup led to general mantle circulation. The deceleration of the African Pla te, due to its collision with the Eurasian Plate, diverts mantle flow westward, increasing the net basal driving torque and westward velocit y of the South American Plate. One result of South America's higher pl ate velocity is the increased cordilleran activity along its western e dge, beginning at about 30 million years ago.