On the extension in western Anatolia and the Aegean sea

Geodynamic reconstructions of the eastern Mediterranean suggesting either westward anatolian extrusion, or gravitational collapse of thickened lithosphere, can be ruled out because plates velocity vectors increase from eastern Anatolia to the Aegean and Greece. This contradicts the basic rule that the velocity field decreases moving away from the source area of the energy, i.e. the supposed squeezing of Anatolia due to the Arabia indenter, or the collapse of the Anatolian orogen. Moreover the topographic gradient between Anatolia and the Ionian deep basin is too small (<1 °) for providing sufficient energy relief able to explain present deformation. The simplistic view of the westward Anatolian escape would rather close the Aegean Sea. We interpret the extension in western Turkey, Aegean sea, Greece and Bulgaria as a result of the differential convergence rates between the northeastward directed subduction of Africa relative to the hangingwall disrupted Eurasian lithosphere. Considering fixed Africa, the faster southeastward motion of Greece relative to Cyprus- Anatolia determines the Aegean extension. A new IERS-based solution is presented. The differences in velocity are ascribed to differential decoupling with the asthenosphere. Unlike west-Pacific backarc basins where the asthenosphere replaces a subducted and retreated slab, the study area represents a different type of extension associated to a subduction zone, where the hangingwall plate overrode the slab at different velocities, implying internal deformation. The slab may be folded by the isostatic rebound of the mantle beneath the ' backarc'rift, and stretched for the increasing length of the slab between Greece and Anatolia. A sort of window then formed both in the slab and between the two upper plates, allowing uprise of mantle derived Na-rich magmas.