TECTONICS OF POST-COLLISIONAL VOLCANISM IN CENOZOIC WESTERN ANATOLIA (TURKEY)

Post-collisional volcanism in western Anatolia followed a continental collision event in the Early Eocene and occurred in discrete pulses that appear to have propagated from north to south over time. The 1st episode evolved during the Eocene & Oligo-Miocene and was sub-alkaline in nature, producing medium- to high-K calcalkaline & shoshonitic rocks. Partial melting and assimilation–fractional crystallization were important processes for the genesis & evolution of the parental magmas, which experienced decreasing subduction influence and increasing crustal contamination through time. Sub-alkaline volcanism coincided with continued regional compression and the development of a thick orogenic crust, and was influenced by an influx of asthenospheric heat & melts provided by slab break-off. The 2nd main episode occurred during 16-14 Ma, producing mildly alkaline rocks that show a decreasing amount of crustal contamination and subduction influence through time. Although melting of a subduction-modified lithospheric mantle continued, an asthenospheric mantle–derived melt contribution played a major role in the generation of mildly alkaline magmas. The inferred asthenospheric melt contribution was a result of lithospheric delamination and/or partial convective removal of the subcontinental lithospheric mantle. The 3rd episode started around ~12 Ma and has continued until the late Quaternary. The melt source carried no subduction component, and the main magma source was decompressional melting of the asthenospheric mantle flowing in beneath the attenuated continental lithosphere in the Aegean extensional province. Lithospheric-scale extensional fault systems provided natural conduits for the transport of uncontaminated alkaline magmas to the surface. The southwestward rollback of the Hellenic subduction zone has resulted in arc volcanism and crustal extension in the Southern Aegean throughout the latest Miocene & Quaternary. The post-collisional volcanism in western Anatolia hence displays compositionally distinct magmatic episodes controlled by slab break-off, lithospheric delamination, asthenospheric upwelling & decompressional melting, and oceanic lithospheric subduction as part of the geodynamic evolution of the eastern Mediterranean region throughout the Cenozoic.