New insights into the dynamics of wedge areas from a 2D numerical study of the effects of shear heating and mantle hydration on an ocean-continent subduction system

To obtain new insights regarding the mechanisms that favor the exhumation of buried crustal material during ocean-continent subduction, we have developed a 2D finite element model that investigates the effects of shear heating and mantle hydration on the dynamics of wedge areas. The development of the model consists of an initial phase of active oceanic subduction and a second phase, after collision, of pure gravitational evolution; in addition, it considers 3 different velocities of active subduction. Our results show that accounting for mantle hydration is essential to produce small-scale convective flows in a wedge area with the consequent recycling and exhumation of subducted material. In addition, the dynamics of hydrated areas are strictly correlated to the thermal state at the external boundaries of the mantle wedge, and the extension of hydrated areas is independent from the subduction velocities when mantle hydration and shear heating are simultaneously considered during the active subduction phase. During the pure gravitational phase, the hydrated portion of the wedge undergoes a progressive enlargement for models with a high subduction velocity during the previous active phase. Finally, a comparison between the predicted P/T ratios and the P-T conditions recorded by markers during subduction, which show metamorphic gradients that are traditionally considered to be distinctive examples of different phases of evolution in an ocean/continent subduction complex, supports the notion that contrasting P-T conditions can contemporaneously characterize different portions of the subduction system during successive phases of modeled subduction-collision.