Constraints on Plate-Tectonic Driving Forces from Seismic Anisotropy

Götz Bokelmann, Stanford University

The mechanism of plate tectonics is one of the most important yet open questions in geosciences. Are the tectonic plates pulled and pushed from the side as the Orowan-Elsasser model (Elsasser, 1969) suggests or does mantle convection play an active role in driving the plates (Holmes, 1933). This question can be addressed by studying the deformation of deep continental roots. The application to North America shown here suggests that the North American plate moves slower than the deeper mantle below the Americas, and that the latter plays an important role in driving the plate. This, together with the positioning of the thick part of the Northamerican plate over a sinking current in the mantle gives a natural explanation for why the motion of North America slowed down dramatically during the last hundred million years. This pattern predicts North American motion to eventually come to a halt.