Geodynamic significance of ophiolites within the Calabrian Arc

Abstract

Slices of oceanic lithosphere belonging to the neo-Tethys realm crop out discontinuously in the northern Calabrian Arc, Southern Apennines. They consist of highpressure-low-temperature metamorphic ophiolitic sequences formed from metaultramafics, metabasites and alternating metapelites, metarenites, marbles and calcschist. Ophiolites occupy an intermediate position in the northern Calabrian Arc nappe pile, situated between overlying Hercynian continental crust and the underlying Apenninic limestone units. In the literature, these ophiolitic sequences are subdivided into several tectonometamorphic units. Geochemical characteristics indicate that metabasites were derived from subalkaline basalts with tholeiitic affinity (transitional mid-oceanic ridge basalt type), and a harzburgitic-lherzolitic protolith is suggested for the serpentinites. The pressure-temperature-deformation paths of the metabasites from different outcrops display similar features: (i) the prograde segment follows a typical Alpine geothermal gradient up to a metamorphic climax at 350 ° C and 0.9 GPa and crystallization of the high-pressure mineral assemblage occurs along a pervasive foliation developed during a compressive tectonic event; and (ii) the retrogression path can be subdivided in two segments, the first is characterized by nearly isothermal decompression to approximately 400 ° C and 0.3 GPa and the second follows a cooling trajectory. During low-pressure conditions, a second deformation event produces millimetric to decametric scale asymmetric folds that describe west-verging major structures. The third deformation event is characterized by brittle extensional structures. The tectonometamorphic evolution of the ophiolitic sequences from the different outcrops is similar. Both thermobarometric modeling and tectonic history indicate that the studied rocks underwent Alpine subduction and exhumation processes as tectonic slices inside a west-verging accretionary wedge. The subduction of oceanic lithosphere was towards the present east; therefore, the Hercynian continental crust, overthrusted on the ophiolitic accretionary wedge after the neo-Tethys closure, was part of the African paleomargin or a continental microplate between Africa and Europe.

Geology map of the central area of Catena Costiera: insights into the tectono-metamorphic evolution of the Alpine belt in Northern Calabria

“…The occurrence of T-MOR basalts with a tholeiitic affinity in both the CC and MG units indicates their origin from the Western Tethys oceanic domain, analogously to the other ophiolite sequences cropping out within the northern Calabrian Arc (Liberi & Piluso, 2009;Liberi et al, 2006). The two ophiolitic units are characterised by thick metasedimentary covers including ophiolitic metarenites and metapelites, previously interpreted as belonging to a pre-Mesozoic continental basement (Bagni unit of Amodio-Morelli et al, 1976;Dietrich & Scandone, 1972).…”

“…The ophiolitic units of the Northern Calabrian Arc are represented by metabasalts with a tholeiitic affinity and T-MORB geochemical signatures and metasedimentary cover ( Figure 2); metaultramafic rocks are present in the Gimigliano-Monte Reventino unit only, whilst gabbros and the sheeted-dike complex are completely absent (Amodio-Morelli et al, 1976;Liberi et al, 2006;Liberi & Piluso, 2009;Spadea, 1979). The Calabrian ophiolites, as well as those from Corsica, Northern Apennines and Alps, are described as incomplete ophiolitic sequences characterised by quite heterogeneous metasedimentary covers showing a noticeable terrigenous supply (Liberi & Piluso, 2009).…”

“…These units are, from bottom to top: -the Apenninic units (Amodio-Morelli et al, 1976), represented by Triassic-Early Miocene successions representative of the Africa continental margin (Amodio-Morelli et al, 1976;Iannace et al, 2007;Ogniben, 1973); -the ophiolitic units, that consist of ophiolites and deep-sea deposits derived from the Western Tethys oceanic basin (Amodio-Morelli et al, 1976;Liberi, Morten, & Piluso, 2006;Liberi and Piluso, 2009;Ogniben, 1973;Spadea, 1994); -the continental units, representative of both lower and upper levels of the continental crust and small volumes of subcontinental upper mantle rocks (Liberi, Piluso, & Langone, 2011;Messina et al, 1994;Piluso & Morten, 2004;Piluso, Cirrincione, & Morten, 2000). Figure 1).…”

Ophiolite‐bearing mélanges in southern Italy

“…All the rocks of this unit are affected by a main foliation with associated rootless intrafolial folds suggesting a large-scale transposition. These rocks show HP-LT metamorphic mineral assemblages (glaucophane, crossite, Mg-riebeckite, jadeite, omphacite, lawsonite and aragonite) occurring along the main foliation, overprinted by a greenschist facies metamorphism (De Roever 1972;Spadea et al 1976;Lanzafame et al 1979;Cello et al 1991;Rossetti et al 2004;Liberi et al 2006). The age of the HP-LT metamorphism has been estimated at the Eocene-Oligocene boundary (Rossetti et al 2001).…”

Tectonic evolution of the Sicilian Thrust System (central Mediterranean)

“…Some au thors have sug gested that the tec tonic units forming the Calabride Com plex orig i nated ei ther from the north ern mar gin of the Af ri can plate (Bonardi et al, 2003) or from a microplate sandwiched be tween the Af ri can and the Eu ro pean plates (Cello et al, 1996;Liberi et al, 2006). How ever, on the ba sis of geo met ric re con struc tions of the Me so zoic sed i mentary se quences, meso-and microstructural ob ser va tions, and palaeomagnetic mea sure ments, the tec tonic units form ing the Calabride Com plex are gen er ally con sid ered to have orig i nated from the south ern Eu ro pean mar gin (Bouillin, 1984;Dietricht, 1988;Bouillin et al, 1992;Gueguen et al, 1998;Rosenbaun et al, 2002;Rosenbaum and Lis ter, 2004).…”