Investigation of geochemical changes in cenozoic plutons in Aegean region

The Aegean region has been focus of extensive plutonism with volcanic counterparts following the amalgamation of continental blocks along the northern Neotethys Suture since the Late Cretaceous to Palaeocene. Eocene to Late Miocene plutonic bodies form overlapping granitoid belts that extend about W-E in direction and display a consistent southerly younging trend. Three major granitoid belts can be defined based on their spatial and temporal position from north to south: (1) Eocene granitoid belt, (2) Oligocene–Early Miocene granitoid belt, and (3) Middle–Late Miocene granitoid belt. The Eocene granitoid belts are suggested to linked to the slab break-off processes, while the roll-back of the Aegean slab was widely accepted to be responsible for the post-collisional extension and the generation of mantle and crustal sources of the Oligocene–Early Miocene and Middle–Late Miocene granitoid belts on the basis of geochemical data. However, lateral variations in the geochemical features of each granitoid belt have not been examined in detail. We compiled whole-rock major and trace element concentrations together with available radiometric age data from the granitoids in the Aegean region in order to correlate their element abundances and to provide insights into the complexities of geodynamic processes. The geochemical changes obtained in the element distribution contour map and box charts for the purpose of examining the geochemical changes in Cenozoic Plutons in the Aegean Region are as follows. SiO2, P2O5, Ce values are low in Early-Middle Eocene granitoids and high in Middle-Late Eocene granitoids. TiO2, Al2O3, MgO, CaO and ACNK / SiO2 contents are high in Early-Middle Eocene granitoids, while being low in Middle-Late Eocene granitoids. The Oligo-Miocene granitoid belt exhibits high Al2O3, TiO2, CaO, MgO, MnO, ACNK/SiO2, Ba and Ba + Yb values and low SiO2 values. Early Miocene granitoids show high values of SiO2, Ba, Ce and Ba + Yb and low values of TiO2, Al2O3, CaO, P2O5, MgO, MnO and ACNK/SiO2. Middle Miocene granitoids have high SiO2 contents and low P2O5, MgO, MnO, ACNK/SiO2, Ba, Ce and Ba + Yb contents. Kos and Samos granitoids, located in the Late Miocene granitoid belt, possess different geochemical characteristics than all other granitoids in the same group. While Late Miocene granitoids have high SiO2 contents and low P2O5, MgO, MnO, ACNK/SiO2, Ba, Ce and Ba + Yb contents, Samos and Kos granitoids have low SiO2 and high P2O5, MgO, MnO, ACNK/SiO2, Ba, Ce and Ba + Yb contents. Two compositionally distinct zones occur in the Eocene granitoid belt. Each zone covers a separate domain and lies in an area of about E-W in direction. Early-Middle Eocene granitoid zone in the south displays more basic compositions with respect to the Middle-Late Eocene granitoids in the north. The Oligocene–Early Miocene granitoid belt, which partly overlaps the Early-Middle Eocene granitoid zone, extends about 400 km along NW-SE in direction. Southeastward younging of plutonism occurs along the strike of the belt. The granitoid bodies have almost uniform geochemical signatures, displaying slightly more acidic affinity towards the youngest pluton within the belt. Middle–Late Miocene granitoids occur in the Western Anatolia in the east and the Cycladic plutonic complex in the west of the Aegean region. These granitoids have almost consistent geochemical signatures. But plutonism in the Anatolia appear to have ceased during Middle Miocene while the Cycladic plutonic bodies continued to occur until Late Miocene. These plutonic bodies are accompanied by the Samos and Kos intrusions located between Anatolian and Cycladic granitoid zones, showing distinctly more primitive compositions associated with mantle input. All these characteristics of these granitoid belts in the Aegean region suggest that the origin of the Eocene granitoid belts is diverse and implies different geodynamic scenario than simple slab roll-back model to explain the generation of the Oligocene and Miocene granitoid bodies in the Aegean region. Particularly, significant geochemical variations in the Oligocene-Early Miocene and Middle-Late Miocene granitoid belts reflect the effects of diverse tectonic settings in the origin of plutonism rather than long-term slab-roll back of the Aegean lithosphere.