Mantle degassin on a near shore submarine volcano, SE Tyrrhenian Sea

The presence of a seamount-like structure, located few nautical miles offshore the Capo Vaticano Promontory (western Calabria, S Italy), was revealed by combined geophysical and geochemical investigation. The edifice is ~55 km2-wide, with a top located at a depth of about 70 meters below sea level, is mainly composed by a NW-trending structure orthogonally interrupted by minor ridges, the largest of which being affected by extensional faults. The top of the edifice hosts active vents injecting fluids that have been investigated for the dissolved volatiles. Gas analyses revealed high CO2 and CH4 contents, several orders of magnitude above the atmospheric-type values expected for shallow, coastal marine waters, besides a noteworthy enrichment in mantle-derived 3He, representing an unambiguous indicator of the mantle origin of fluids. Our results, combined with available data from the literature, suggest that the edifice is a tectonically-controlled volcanic system, which presence near Calabria region changes the role played by faults in frame of the subduction process.