Subduction-induced break-up and drifting of continental plates

Since the early theory of Wegener, the break-up and drift of continents have been controversial and hotly debated topics. To assist the interpretation of the break-up and drift mechanisms and its relation with mantle circulation patterns, we carried out a 2-D numerical study that will provide insight into the dynamics of these processes. Different regimes of upper plate deformation are studied as consequence of stress coupling with mantle convection patterns. The most important results indicate that three different styles of subduction can be defined by increasing the viscosity contrast between upper and lower mantle: penetrating slab, slab avalanche and stagnant slab. Subduction of the oceanic plate induces mantle flow that, in turn, exerts basal tractions on the upper plate. These acting mantle drag forces (FMD) can be subdivided in two types: (1) active mantle drag occurring when the flow drives plate motion (FAD), and (2) passive mantle drag (FPD), when the asthenosphere resists plate motion. The active traction generated by the subduction-induced convective cell is counterbalanced by passive mantle viscous drag away from it and therefore tension is generated within the continental plate. The shear stress profiles indicate that break-up conditions are met where the gradient of the basal shear stress is maximized. However the break-up location varies largely depending on the convection style primarily controlled by slab stagnation on the transition zone or by slab penetration into the lower mantle. Our study, compared with real subduction settings, suggests that: (1) The stagnating slab models with break-up at about 250-350 km from the trench and drifting of small continental portions can be compared with the evolution of the Japan Arc and the opening of the Western Mediterranean, where stagnant slabs and microcontinents migrated following the retreat of the Pacific and Ionian slab, respectively. (2) The penetrating slab model with break-up at about 2800-3500 km from the trench and drifting of large continental plates could explain the opening of the Atlantic Ocean and westward drifting of the South and North American Plates following the retreat of the ⇠15000 km wide Farallon Plate. Good correspondences between our models and these convergent margins provide an alternative interpretation for their evolution and, more in general, for the break-up and drifting mechanisms of continents.