CRUSTAL ARCHITECTURE AND TECTONIC EVOLUTION OF THE ANATOLIAN-AFRICAN PLATE BOUNDARY AND THE CENOZOIC OROGENIC BELTS IN THE EASTERN MEDITERRANEAN REGION

The modern Anatolian-African plate boundary is characterized by subduction zone tectonics and is in the initial stages of collision-driven orogenic buildup. The Anatolian microplate itself is made of young orogenic belts (Eocene and younger) that evolved during a series of collisions between Gondwana-derived ribbon continents and trench-rollback systems within the Tethyan realm. The collision of the Eratosthenes seamount with the Cyprus trench since the late Miocene is a smaller-scale example of this accretionary process and has affected the slab geometry and kinematics of the subducting African lithosphere. Pn velocity and Sn attenuation tomography results show that the uppermost mantle beneath much of the young orogenic belts in Anatolia is anomalously hot and thin. This is consistent with the surface geology, which is dominantly controlled by strike-slip and extensional tectonics and widespread volcanism in western, central and eastern Turkey. In all these areas, the extension was well under way by the late Oligocene-Miocene, following the main episodes of continental collisions. Pinning of subduction hinge zones by the accreted ribbon continents arrested slab rollback processes, causing terrane stacking and crustal thickening, and resulted in slab breakoff because of continued convergence of the lithospheric mantle. Slab breakoff-induced asthenospheric upwelling provided the necessary heat and melt to produce the first phases of post-collisional magmatism in these young orogenic belts. Renewed subduction and slab rollback in the Tethyan realm triggered lithospheric-scale extension in the upper plate, and the thermally weakened orogenic crust started collapsing. These processes resulted in rapid exhumation of recently formed high-pressure metamorphic rocks and in the formation of metamorphic core complexes. The Cenozoic geodynamic evolution of the western, central, and eastern Anatolian orogenic belts indicates that the asthenospheric mantle beneath collision zones responds swiftly to crustal tectonics on time scales of just a few million years. Slab breakoff, lithospheric delamination, and slab tearing were common processes that resulted directly from collision-induced events, and caused convective remobilization of the asthenosphere leading to magmatism. Asthenospheric upwelling and partial melting played a major role in a geochemical progression of post-collisional magmatism from initial shoshonitic, calc-alkaline to late-stage alkaline affinities through time. The collision-driven tectonic evolution of the Anatolian-African plate boundary and the young orogenic belts in the eastern Mediterranean region is typical of the geodynamic development of the Alpine-Himalayan orogenic system. Successive collisions of Gondwana-derived microcontinents with trench-rollback cycles in the Tethyan realms of the Alpine-Himalayan system caused basin collapse, ophiolite emplacement, and continental accretion, producing subparallel mountain belts. Subduction of the Tethyan mantle lithosphere was nearly continuous throughout these accretionary processes, only temporarily punctuated by slab breakoff events.