Tertiary to Quaternary evolution of volcanism in the Aegean region

Summary Widespread orogenic volcanic activity has continued in the Aegean area from the Oligocene to present. Two main phases of activity are recognized. One developed in the North Aegean area from Oligocene to Middle Miocene times and a second started in the Pliocene, building the active South Aegean volcanic arc. Between these two phases, Upper Miocene to Quaternary volcanism of variable petrogenetic affinity occurred to a limited extent, essentially on the margins of the Aegean microplate. The products erupted during the Oligo-Miocene phase consist mainly of calc-alkaline and shoshonitic intermediate lavas and pyroclastics with minor acidic and basic rock types. The volcanic activity started in the northernmost part of the North Aegean area with mostly calc-alkaline intermediate and acidic volcanics. The volcanism shifted successively southwards becoming progressively enriched in potassium. This evolution is interpreted as being related to an increase in the dip of the Benioff zone under the Eurasian plate, resulting from a reduction in the plate convergence rate after continental collision. The volcanic products of the active south Aegean arc are mainly andesites with minor basalts and rhyolites which display the chemical character typical of calc-alkaline series erupted on thin continental margins. The South Aegean arc is believed to be the surface expression of active subduction of the African plate. Scattered Upper Miocene to Quaternary activity is interpreted as occurring in zones of tensional strain along the borders of the Aegean microplate.