Tectonometamorphic evolution of the ophiolitic sequences from Northern Calabrian Arc

Ophiolites crop out discontinuously in the Northern Calabrian Arc (Southern Italy). They consist of high pressure/low temperature metamorphic ophiolitic sequences of Late Jurassic-?Early Cretaceous age, in which a metabasic and metaultramafic association is the base of a complex metasedimentary cover ranging from pelagic to flyschoid type sediments. These ophiolitic sequences, interpreted as slices of oceanic lithosphere belonging to the Jurassic Tethys realm, occupy an intermediate position in the northern Calabrian Arc nappe pile, between the overlying Hercynian continental lithosphere (Calabride nappe) and the underlying Apenninic carbonate units.In the literature, these ophiolitic sequences are subdivided into several tectonometamorphic units; some authors distinguished between an upper slightly metamorphic ophiolitic unit and a lower HP-metamorphic ophiolitic unit. This subdivision contrasts with new petrological data and geothermobarometric modelling. In fact, the overall P-T evolution for several ophiolitic sequences from the northern Calabrian arc describes comparable paths, characterized by a HP-LT metamorphism followed by retrogression under greenschist facies conditions. The metamorphic climax is calculated at pressures ranging between 0,9 and 1,1 GPa and a temperature around 380°C.Moreover, structural analysis of rocks characterized by HP syn-metamorphic ductile deformation suggests that tectonic evolution is quite homogeneous and similar, although different degrees of deformation can be observed. The high-pressure mineral assemblage defines a pervasive foliation developed during a compressive tectonic event (D1) that transposed the earlier structures. A second tectonic event (D2) which occurred during decompression at 0,4 GPa, produced millimetre to decametre scale asymmetric folds. Later extensional brittle structures are responsible for final exhumation of the HP rocks.The tectonometamorphic evolution of the ophiolitic sequences of Northern Calabrian Arc is well explained in a context in which the oceanic-derived rocks underwent subduction and exhumation as tectonic slices inside an accretionary wedge.

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