Geology of the northwestern portion of the Ferriere-Mollieres Shear Zone, Argentera Massif, Italy

The Ferriere-Mollieres Shear Zone (FMSZ) is a regional shear zone cross-cutting the Argentera External Crystalline Massif (Western Alps). It shows a NW-SE striking dextral shear zone separating two Variscan migmatitic complexes: the Tinee to the SW and the Gesso-Stura-Vesubie to the NE. Geological-structural mapping at 1: 10,000 scale focused on the characterization of mylonitic deformation. A deformation gradient has been observed towards the core of the shear zone marked by the occurrence of ultramylonites and rare phyllonitic layers. Protomylonites passing to unsheared migmatites occur in the outer zones. Low-angle shear zones with a top-to-the S and SW sense of shear cross-cut the previous mylonitic foliation. The FMSZ is a Variscan transpressive shear zone activated during the Late Carboniferous under amphibolite-facies metamorphic condition. The shear zone has been partially reactivated under greenschist-facies metamorphic conditions during Alpine Orogenesis.