AN OCEANIC CORE COMPLEX PRESERVED IN OPHIOLITIC FRAGMENTS IN CALABRIA, SOUTHERN ITALY

Dismembered fragments of Jurassic Alpine Tethys ocean crust are exposed in the Cenozoic accretionary complex of Calabria, Southern Italy. Most of the ophiolite consist of prehnite-pumpellyite to lawsonite-blueschist-facies metabasalt and associated sedimentary cover. However, in the southernmost exposures, at Gimigliano and Monte Reventino (above Lamezia Terme), greenstone metabasalt is closely associated with serpentinite and ophicarbonate. At Gimigliano, serpentinite underlies a thick sequence of metabasalt, while at Monte Reventino, the contact between the two units is has been folded by Alpine deformation, with serpentinite at the core of a 200-m fold. The close relationship between metabasalt and serpentinite requires an explanation.

At Monte Reventino, rodingite dikes within the serpentinite are truncated at the metabasalt-serpentinite contact, suggesting that the contact is a fault. Serpentinite in the footwall of the fault has been altered to tectonic ophicarbonate by subseafloor fluid flow and further altered to talc-tremolite schist near the fault surface. At Gimigliano serpentinite breccias forms lenses within the metabasalt, indicating that serpentinite was exposed on the ocean floor when basalt was being erupted. These observations are similar to what has been reported from the Chenaillet Ophiolite (French-Italian Alps), where low-angle normal faulting and a reduced magma supply suggest an original tectonic setting of an oceanic core complex at a slow-spreading paleoridge.

It is not clear whether the overlying basalt was deposited on the detachment surface of a low-angle fault, or if the basalts were juxtaposed against serpentinite by slip along a normal fault. However, similar outcrops near Terranova di Pollino in Northern Calabria expose pillow basalt and radiolarian chert that appear to be in depositional contact with a serpentinite, suggesting that at that locality basalt was erupted onto an exhumed fault surface.