Calabria - Lucania ophiolites

Available data indicate that the Calabria-Lucania ophiolites may be considered fragments of the oceanic lithosphere developed during the Jurassic opening of the Western Tethyan basin separating the European and Insubrian continental blocks. The primary rock assemblage includes: mantle ultramafics mostly of spinel-lherzolite character; cumulus gabbros derived from MORIB-type tholeiitic magmas ai various fractional crystallization stages; basaltic extrusives showing a mostly undepleted tholeiitic composition of transitional MORB type. The sedimentary cover includes radiolarian chert of late Jurassic age. In primary characteristics they are similar to the ophiolites from the Western Alps, Northern Apennines and Corsica, particularly to the External Liguride sequences of the Northern Apennines. An origin in a pericontinental position is supported by the primary stratigraphical relationships with continental rocks from the lower crust and terrigenous sequences. Their tectonic-metamorphic evolution included dismemberment, subduction-related high-pressure and low-temperature (HP/LT) metamorphism, and emplacement as distinct tectonic units. The distribution and inferred age of the HP/LT metamorphism indicate that the ophiolites from the Lucanian Apennines and the Calabrian Arc represent two distinct belts. One includes the blueschist facies ophiolites of the Calabrian Arc, which record an Eoalpine tectonic-metamorphic evolution assigned to the Cretaceous-Paleogene. A second belt includes the metaophiolites and associated metasedimentary rocks of the Lucanian Apennines which record a later tectonic event assigned to the late Oligocene-early Miocene. The high-pressure and very low-temperature conditions of the post-late Oligocene metamorphic event can be accounted for in a subduction environment. it is suggested that in the Calabria-Lucania sector, Western Tethys underwent fragmentation of the oceanic lithosphere (or crust) and subsequent diachronous closure, including a mid-Tertiary stage, ai the time when continental collision is known to have occurred in other sectors of the Alpine-Apennine system. The hypothesis of a mid Tertiary subduction has important implications for the geodynamic relationships of the Oligocene-Miocene calc-alkaline volcanism represented in the peri-Tyrrhenian area.