2D numerical study of the effects of mantle hydration and viscous heating on the dynamics of the wedge area within an ocean/continent subduction complex: the case study of Variscan crust in the Alpine domain

The geodynamics of a convergent ocean/continent margin, evolving from subduction to continental collision, was analyzed by means of a 2D finite element thermo-mechanical model, in which the physics of the crust-mantle system is described by the equations for continuity, conservation of momentum and conservation of energy. A viscous behavior for the whole system and density and viscosity depending from both temperature and composition are assumed. Different values of convergence velocities, 3, 5 and 8 cm/yr, have been used, as representative of slow, medium and fast subductions. Our analysis is particularly focused on the effects of viscous heating and mantle hydration on the dynamics in the wedge area. The results support that both mechanisms induce the development of short wavelength convective cells in the wedge area that favor the exhumation of subducted crustal material since the early stages of the subduction. Model predictions, in terms of pressure, temperature, lithology and age, have been compared with the structural, petrological and age natural data from the Variscan crust of the Alpine domain.