Alpine shear zone reworking Variscan rocks in the Sila Piccola Massif (Northern Calabria)

Petrological and microstructural investigations focused on a portion of the lower-intermediate continental crust of the Calabrian crystalline basement have been carried out near the village of Castagna (northern Calabria). In particular, a mylonitic horizon affecting granulite facies rocks of the Sila Unit has been studied and an Alpine metamorphic shearing imprint superposed on earlier high temperature Variscan relics has been recognised. Such earlier preserved assemblages, occurring as low strain domains of garnet-sillimanite paragneiss within the pervasive mylonitic foliation, consist of intermediate to low Ti-biotite and oligoclaseandesine plagioclase. The compositional garnet profile indicates a likely re-homogenisation of cores suggesting a long time residence at high T conditions in the lower crust. A subsequent Alpine mylonitic overprint generates retrograde metamorphism at upper amphibolite facies conditions possibly representing a “detachment zone”, responsible for the exhumation of the deepest parts of the continental crust, reworked during the building of the Alpine Orogen.