Submagmatic to solid-state shear-related deformation in late Variscan granitoids from a polyorogenic mountain belt (Peloritani Mountains, southern Italy)

Late Variscan granitoid rocks (c. 310-300 Ma) of trondhjemitic and granitic composition, intruded in migmatitic paragneisses in the north-eastern Peloritani Mountains (Fiannacca et al., 2019), exhibit a range of deformation microstructures developed under simple-shear regime at decreasing temperatures, such as sigmoidal feldspar porphyroclasts, mica fish, and asymmetric boudins developed both in muscovite and tiny andalusite crystals. The Peloritani Mountains were involved in three orogenies, i.e. Cadomian, Variscan and Alpine-Apennine, with shear-zone activity so far clearly documented only for the latter (Cirrincione et al., 2015). Nevertheless, some microstructures (e.g. diffuse chessboard pattern in quartz) suggest late Variscan shearing during granitoid cooling, indicating deformation at high-temperature conditions (>650 °C). Submagmatic deformation was extensively superseded by deformation at lower temperatures. Recorded examples of solid state-high temperature deformation-related microstructures (>450°C) include quartz grain boundary migration recrystallization, quartz ribbons and core-and-mantle structures. Low temperature subsolidus microstructures (<450 °C) consist of bulging, subgrain rotation recrystallization, mica kinks and feldspar bending. Subsequent crystallization in sheared micro-domains of undeformed plagioclase from metasomatic fluids likely released by younger late Variscan granitoids (c. 297-292 Ma; Fiannacca et al., 2017), further brackets the shearing event during the latest stages of the Variscan Orogeny in southern Italy.