The evolution of the volcanism in the Eastern Aegean (Greece)
Authors:   , Böhm Katharina 
Published: November 2023

Since the Cretaceous the evolution of the Aegean subduction zone has been controlled by convergence and northward subduction of the African plate beneath the Eurasian plate. Additionally, the realm is dominated by the westward extrusion of Anatolia and north-south extension in the Aegean. Satellite based velocity field measurements show that Anatolia is extruding to the west along the North Anatolian Fault zone, while the southern part of the Aegean domain is moving southward. The southward movement is facilitated by subduction transform edge propagator (STEP) faults in the east and west of the Aegean subduction zone, which mark the transition between the Aegean slab and the Cyprus slab. The southern Aegean domain moves faster to the south than Anatolia is moving to the west and a southward directed sub-lithospheric mantle flow is coupled with slab rollback. This is in agreement with the extensional tectonic processes in the Aegean back-arc. Furthermore, subduction-related processes, including collision and subduction of micro-continents, magma generation at different depth, addition of slab-derived fluids, assimilation, fractionation and magma mixing, add to the diversification of magmatic products. In addition, intra-plate magmatic processes, such as asthenospheric mantle upwelling, are facilitated by slab rollback, slab edge and an approximately vertical gap between the neighbouring Aegean and Cyprus slabs. The seismic anomaly of the gap is situated underneath western Anatolia and reaches in shallower levels into the eastern Aegean.
Back-arc tectonic processes, subduction-related processes and intra-plate magmatic processes result diverse Cenozoic magmatic activities. The central aim of this study is the chemical characterization of the magmatic evolution and the timing of Miocene to Quaternary volcanism in the Eastern Aegean. Questions which follow from this aim are: Which magma fluxes from which mantle source are documented in the (isotope) geochemistry of the volcanic rocks? Did assimilation of the upper or lower continental crust play a role in magma evolution? When and how fast tectonics or slab dynamics facilitated pathways for upwelling of enriched mantle? Was (micro-)-continental crust, or sediment subducted and assimilated? And at which stage in time and which geographical (island) location?
To elucidate the evolution of the Aegean volcanism throughout the Miocene until recent I sampled four islands in the Eastern Aegean Sea: Lesbos, Chios, Patmos and Kos. Here, I present new radiogenic Pb-Sr-Nd-Hf isotope, major- and trace-element data for 45 Miocene to recent volcanic rocks of these four islands. The proportions of subduction component, assimilation of arc crust, contamination by subducted micro-continents and contribution of an enriched mantle source are different at all sampled volcanic islands. In addition to the geochemical analyses, I obtained new high precision – high-resolution 40Ar/39Ar age constraints for the same volcanic rock samples.
The new data adds to the knowledge about the geodynamic evolution of the (eastern) Aegean over the past 23 Ma years and shows the interaction of subduction, accretion, arc migration, tectonics, slab dynamics and mantle flow. The oldest dated volcanic rocks of Lesbos were generated by continental subduction, including subduction of Triassic volcanics from the Tripolitza nappe. During early Miocene, crustal assimilation was maximal and then gradually decreased. Likewise also the subduction signature decreased from early to middle Miocene. The lowest subduction signature and influence of upwelling high-Nb asthenospheric mantle is found in the middle Miocene volcanic rocks of Chios. An asthenospheric influence is also observed in the late Miocene rocks of Patmos, but decreases in the Pliocene, when sub-continental lithospheric mantle dominates the geochemical signature. In the Pliocene – Pleistocene volcanic rocks of Kos, a second pulse of upwelling enriched mantle is detected.