Calabria
The nappe-structured belt of the Calabria-Peloritani orogen is a part of the peri-Mediterranean Alpine system that progressively drifted during the Neogene to Recent opening of the South Tyrrhenian basin and the subduction of the Ionian slab (e.g., Amodio Morelli et al., 1976; Dewey et al., 1989). Its structure and evolution has been classically separated from that of the Apennines, based on the exposed rock types and the evidence for pre-Neogene tectonism. It is unclear whether the Calabria block formed part of the European continental palaeomargin (e.g., Boullin et al. 1986; Cello et al. 1996; Jolivet and Faccenna 2000; Rossetti et al. 2001) or resulted at least in part from earlier periods of northwestward accretion and/or microplate collision and amalgamation (e.g. Amodio Morelli et al., 1976; Grandjacquet and Mascle 1978; Bonardi et al., 2001, Tortorici et al., 2009).
In the northern part of the Calabria, three main groups of nappes may be distinguished: (1) crystalline basement nappes; (2) ophiolite-bearing nappes; (3) mostly calcareous nappes derived from the inner part of the Apulia continental margin. Group (1) includes Variscan metamorphic rocks and granitoids, and Mesozoic low-grade metasedimentary cover of the Bagni Units and sedimentary cover of the Sila Unit (Iannace et al., 2007). These overlie ophiolite-bearing units ranging from greenschist-facies (Malvito unit) to blueschist-facies (Diamante-Terranova unit). Some of these units, the HP–VLT Frido unit and the unmetamorphosed North Calabrian unit (Bonardi et al., 1988), crop out NE of the Pollino Massif. The ophiolite-bearing units tectonically overlie tectonic units of the southern Apennines fold and thrust belt, derived from Miocene to early Pleistocene deformation of the sedimentary cover of the Apulia passive margin. These tectonic units (group 3) are dominated by Mesozoic–Neogene sedimentary successions comprising kilometre-thick, shallow-water to slope carbonates and pelagic basin cherts, limestones and pelites, as well as a complex pattern of Neogene–Quaternary siliciclastic strata deposited in thrust-top and foredeep basin environments. Farther to the south, in the Aspromonte Massif only crystalline basement nappes are exposed.
The pre-Alpine history of the Calabria block is poorly defined. However radiometric data and rare occurences of Paleozoic fossils indicate that the entire basement was affected by Variscan-age metamorphism, locally superimposed on an older high grade metamorphic event (Bonardi et al., 2001).
The first stage of the Alpine orogenic cycle was the result of subduction of Neotethyan oceanic litosphere between the Cretaceous and the Neogene. This led to the opening of the Ligurian Sea Basin, the formation of the Ligurian accretionary wedge (Knott, 1987), the Corsica-Sardinia rotation and major calc-alkaline volcanism in Sardinia (Savelli et al., 1979). This phase of activity ceased during the Burdigalian around 18 Ma (Montigny et al., 1981). Then a second compressive phase occured during the middle Miocene causing collision and emplacement of the Calabrian basement rocks on to the African and Adria plate margin.
Extensional tectonics overprinted Alpine and Apennine compressive events as suggested by Rossetti et al. (2001) on the basis of structural and petrophysical investigation. These authors documented that the Alpine- (west directed) versus Apennine- (east directed) verging structures in north Calabria resulted from the superimposition of a top-to-the-west postorogenic extensional shearing onto an early east directed nappe forming event. A similar northwest directed extensional shearing was also reported by Platt and Compagnoni (1990), recognized as responsible for controlling nappe contacts within the Calabrian units exposed in the Aspromonte region of south Calabria. This stage of tectonism was thin-skinned in nature and distrupts much of the pre-Miocene geometry of the crystalline basement rocks (Van Dijk and Okkes, 1991).