Protracted continental collisions argue for continental plates driven by basal traction

Abstract

In plate tectonic theory, collision between two continents should quickly terminate because of continental buoyancy. If convergence is to continue, it should do so at a new subduction zone where oceanic crust can be consumed. The protracted continental collisions in the Alps, Zagros, and Himalayas, which have continued to deform continental crust since the early or middle Cenozoic, are therefore anomalies in standard plate tectonic theory. It is commonly held that plates are driven by slab pull, but this does not account for the continuing Tethyan collisions where the descending slab has detached from the subducting continent. These protracted continental collisions are better explained by horizontal traction of the mantle on the base of deep continental roots, dragging the northern and southern continents together along a Tethyan axis of mantle convergence. “Continental undertow” thus resolves the collision anomaly in plate tectonics.