THE UNIQUE GEODYNAMIC POSITION OF KOLUMBO HYDROTHERMAL VENT FIELD, NE OF SANTORINI ISLAND, GREECE

Submarine hydrothermal systems associated to recent or active volcanic arcs show a number of geobiological characteristics depending on their geodynamic setting. Most cases reported in the literature concern primarily diverging plate boundaries along Mid Ocean Ridges and secondarily converging plate boundaries along intraoceanic island arcs (e.g. Philippines) or along subduction systems beneath active continental margins with presence of back arc marginal basins (e.g. Japan). These convergent geodynamic environments are contrasted by the oceanic subduction beneath active continental margins without back arc basins with volcanic belts forming mountain belts (e.g. Andes). A transitional situation exists in some converging plate boundaries, where the active continental margin hosts a back arc molassic basin on top of a thinned continental crust without creation of marginal basin as this is observed in the Hellenic arc and in the Taupo rift in New Zealand. The Kolumbo submarine volcano hydrothermal system occurring at 500m depth, is part of the Hellenic volcanic arc developed on top of the subducted East Mediterranean oceanic crust (northern edge of the African plate) beneath the Hellenic Active continental margin (southern edge of the European plate). Its geodynamic position is unique as it lies on top of the Aegean continental crust behind the Hellenic arc and trench system. The geobiochemical characteristics of the Kolumbo hydrothermal system, which resulted from our analyses of samples obtained during recent oceanographic missions, shown extreme concentration of Sb and Tl and the occurrence of archaea and bacteria indicating extreme environments. The correlation of the analyzed data show some familiarities with hydrothermal systems developed within back arc basins along active continental margins and strong differences with those developed in Mid Ocean Ridges.