Strain partitioning and metamorphism in a deformable orogenic wedge: Application to the Alpine belt

Abstract

Various processes have been proposed in the literature to explain the exhumation and preservation of blueschist and eclogitic facies rocks. Among these processes, corner flow circulation within an accretionary wedge is frequently advocated. In the Alpine collisional belt, geological, petrological and chronological evidences indicate that high-pressure low-temperature metamorphic rocks have been generated in the subduction zones which existed before the collisional event. Indeed, the internal part of the Alps have been compared to the inner zone of modern accretionary prisms. In order to discuss the corner flow circulation model and its applications to the internal part of the Alps taking into account the metamorphic and structural data, we have numerically explored in a deformable orogenic wedge: (1) the possible generation of HP-LT metamorphism in this context and the PTt paths related to the exhumation process; (2) the duration of the exhumation; and (3) the strain partitioning and the related geometries imposed by this circulation. The velocity field is computed from mass conservation law. No attempt has been made to include variable viscosity. We show that: (1) HP-LT metamorphism can be achieved in the computed conditions, PTt paths differ according to the velocity of subduction; (2) the exhumation process lasts less than 15 Ma and generates high strains which erase the initial deformation phases; and (3) metamorphic and structural data from the internal part of the Alps are compatible with the numerical constraints.