LAUSR

Recent seismic observations challenge the conventional view that tectonic plates are driven by slab pull and ridge push forces. The observations indicate that the asthenosphere flows faster and in a different direction than the plate above. Previous mantle convection models argued that pressure‐driven flow, in combination with a non‐Newtonian upper mantle, can account for these observations. We expand those models by introducing a formulation that allows for the development of weak plate margins. Weak plate margins lead to an increase in the ratio of slab‐driven to pressure‐driven asthenosphere flow, but pressure‐driven flow remains active and increases with plate margin strength. Locally, the asthenosphere can drive plates and can change flow direction with depth. Furthermore, a non‐Newtonian upper mantle allows for a hysteresis effect where, depending on initial conditions, single‐plate and plate tectonic modes can exist at the same parameter conditions.