Orogenic evolution of the northern Calabria−southern Apennines system in the framework of the Alpine chains in the central-western Mediterranean area

The northern Calabrian ranges and the southern Apennines are part of a single orogenic segment of the Alpine chain system framing the central-western Mediterranean Sea. Three main tectonic complexes characterize this orogenic chain: (1) remnants of the overriding plate, including Variscan Paleozoic basement (Calabria-Peloritani terrane), which tectonically cover (2) an Alpine metamorphic belt, corresponding to an exhumed subduction channel, formed by slices of the Calabria-Peloritani terrane, meta-ophiolites (metamorphic Ligurian Units), and some successions of the continental Adria plate (downgoing plate), which are in turn superposed onto (3) a fold-and-thrust belt composed of remnants of an oceanic accretionary prism (nonmetamorphic Ligurian Units) on the top and an underlying imbricate orogenic pile consisting of shallow-water to pelagic continental Adria successions, also including buried shallow-water carbonates of the Apulian Platform. The exposed Apulian Platform domain (Puglia region) and the Adriatic Sea represent the current foreland. The orogenic chain results from the subduction of Ligurian Ocean lithosphere beneath the European plate/Calabria-Peloritani terrane starting during the Paleocene−Eocene. The restored mean tectonic vergences indicate that the thrust front migrated to the south in the Eocene−Langhian period, turning to the east during the Serravallian−Pleistocene interval. After the complete closure of the Ligurian Ocean in the Early Miocene, the subduction continued with the involvement of the continental part of the Adria plate, triggering crustal shortening until the middle Pleistocene. Complex geometries, reflecting the articulated paleogeographic domains formed by alternating shallow-water carbonate platforms and deep basins, controlled the shape of the thrust front−foredeep−forebulge system. Thin- and thick-skinned thrusting episodes have alternated during the orogenic shortening; however, since the early Pliocene, deep-seated, ramp-dominated thrust faults have driven the crustal shortening, resulting in widespread envelopment thrusting, and out-of-sequence structures in the allochthonous wedge. The alternating different tectonic styles also resulted from the involvement in the subduction system of the continental Adria lithosphere, which is thicker under the carbonate platforms and thinner under the interspersed pelagic basins and the western margin facing the Ligurian Ocean. The involvement of thicker lithosphere during the subduction process caused two main backstops that triggered thick-skinned tectonics. The synorogenic sedimentation was ruled by the migration of the forebulge-foreland basin system, with flexure of the continental part of the Adria plate since the Oligocene and erosion of a large part of the Apennine and Apulian carbonates that fed the foredeep basins with calciclastic supply. Siliciclastic input, which originated from both the overriding plate and orogenic wedge, joined with orogenic volcaniclastics, marks the sedimentation in the foreland basin system, including the mature stage of the foredeep troughs and the wedge-top basins located on the top of the chain, with the latter also recording calciclastic sedimentation that originated from the erosion of the piled-up Adria carbonate successions.