Abstract
I will address issues associated with the forces driving plate tectonics and initiating new subduction zones from two perspectives. A common thread is the origin and evolution of the intense back arc spreading and rapid roll back associated with some ocean-ocean subduction zones. First, I will look at the dynamics driving global plate motions. Then, I will look at the time-dependence of trench rollback regionally. Plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries, but observationally constrained high-resolution models of global mantle flow have remained a computational challenge. We capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions, with individual plate margins resolved down to a scale of 1 kilometer. Cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high-viscosity slabs, altering the velocity of oceanic plates. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. I will show that most back arc extension follows subduction initiation and show how this arises in dynamic models. I will show how we moving global flow models from forward to inverse models.