Petrology and volcanology of Kimolos and Polyegos volcanoes within the context of the South Aegean arc, Greece

Partial melting of a mid-ocean-ridge basalt (MORB)–like asthenospheric mantle, metasomatized by subducted sediments and aqueous fl uids, is thought to have produced all the South Aegean arc parental magmas. According to west-east isotopic trends, the amount of subducted sediments involved in the magma genesis decreases from west to east, together with a possible change in the composition of the subducted sediments. The lowest fl uids to sediment-melts proportions are involved in the genesis of Santorini magmas, whereas the highest are involved in the magma genesis at Milos and Nisyros volcanic fi elds. The aqueous fl uids should derive from subducted oceanic crust, at least in the central and eastern sectors of the arc. Most of the geochemical characteristics of the Santorini magmas are explained by higher partial melting degrees of the mantle source, probably triggered by the greater lithosphere extension, which induces adiabatic upwelling of the mantle. The higher lithosphere extension also causes Santorini magmas to reside at shallower levels, thus preventing amphibole crystallization and allowing a higher amount of mafi c magmas to reach the surface. The Nisyros parental magmas are, on the contrary, generated by the least amounts of partial melting of the mantle. Partial melting of the mantle source seems to increase with time and passing from the external toward the central sectors of the arc.