Mantle pressure gradient as a novel driver for plate motion and intraplate tectonism

Driving forces of plate tectonics remain a fundamental question of geodynamics. Traditional research on this topic heavily replies on theoretical analysis or simple numerical experiments with assumptions that may not be applicable to the real Earth. For example, the concept of slab pull assumes that the total negative buoyancy of the upper-mantle slab readily transmits to the tectonic plate at the surface, while in reality most of this force would be accommodated by the disturbed ambient mantle. In addition, many numerical models evaluating plate driving forces usually assume a regional geometry and neglect the dynamic effects of other subduction systems. More importantly, most previous studies investigating plate driving forces used plate kinematics as key constraints and failed to provide quantitative force measurements.

We revisit the driving mechanisms of plate motion and intraplate tectonism using state-of-the-art 4D global convection models with data assimilation that simultaneously consider all subduction systems according to recent plate reconstructions. These models also utilize realistic rheology and convection vigor, implemented on a high-resolution (locally achieving ~5 km) numerical mesh. We avoided any analytical approximation by directly measuring the values of various forces predicted from the model. We find that most of the negative buoyancy of the slab fails to transmit to the surface plate. On the other hand, lateral pressure gradients widely exist inside the mantle that present a previously unrecognized driving mechanism for various surface tectonism. The pressure gradient across the slab hinge provides a force that usually points in the direction of subduction and plate motion. In major continental collision zones, even without the presence of active subduction, this force may sustain the surface convergence by dragging the underside of lithosphere. Temporally, this lateral pressure gradient grows as subduction continues, reducing the slab dip angel and eventually tearing the young slab. Then prominent landward mantle wind occurs that further interacts with the overriding continent to form complex intraplate processes.