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 degrees C for the structurally highest units and 3-4 kbar at 380-440 degrees 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 degrees C km(-1)) to a Barrovian-type (28-36 degrees 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.