Variscan shear deformation in the Argentera Massif: A field guide to the excursion in the Pontebernardo valley (CN, Italy)

After a short geologic overview of the Variscan Belt in the Mediterranean Area and of the Alpine External Crystalline Massifs a field trip in the northern sector of the Argentera Massif is described. The itinerary is subdivided in six stops located along a transect that allows to observe a complete section of the Ferriere-Mollières shear zone, the main regional-scale ductile shear zone cross-cutting the Argentera Massif. This shear zone, developed at the expense of Variscan migmatites, is characterized by a deformation gradient along which a transition from protomylonites, to mylonites and to ultramylonites is welldetectable. Structural and micro-structural analysis joined with the study of kinematic vorticity allowed to recognize a transpressive deformation with variation in the percentage of pure shear and simple shear along the deformation gradient and an evolution of the shear zone from high-temperature to low-temperature conditions.