Styles and regimes of orogenic thickening in the Peloritani Mountains (Sicily, Italy): new constraints on the tectono-metamorphic evolution of the Apennine belt

The Peloritani Mountains constitute the Sicilian portion of the Calabria–Peloritani Arc (Italy), a tectono-metamorphic edifice recording the history of the subduction–exhumation cycle during Tertiary convergence between the African and European plates. Here, we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental-derived metamorphic units cropping out in the eastern portion of the Peloritani Mountains. Both meso- and micro-scale shear sense criteria indicate a top-to-the-SSE tectonic transport, during a general evolution from ductile to brittle deformation conditions. Quantitative thermobarometry on texturally equilibrated phengite–chlorite pairs crystallized along the shear bands indicates pressure of 6–8 kbar at temperatures of 360–440 °C for the structurally highest units and 3–4 kbar at 380–440 °C for the lowest ones. This documents an overall inverse-type nappe arrangement within the tectonic edifice and a transition from an Alpine- (13–18 °C km−1) to a Barrovian-type (28–36 °C km−1) geothermal gradient during the progress of the Alpine orogenic metamorphism in the Peloritani Mountains. The integration of these results allows the Peloritani Mountains to be considered as a constituent element of the Apennine orogenic domain formed during the progressive space–time transition from oceanic to continental subduction at the active convergent margin.