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Several lines of evidence indicate that NW Anatolia was characterized by widespread strike-slip tectonism during Late Eocene-Oligocene time, following the closure of the Izmir-Ankara ocean and the continental collision between the Pontide and the Anatolide-Tauride domains. (i) Granitoid bodies (Uludag, Kapidagi, Marmara Island) of Late Eocene-Oligocene age show synkinematic near-vertical foliation with a consistent strike and a nearly horizontal lineation pointing to a right-lateral shear sense. (ii) Apatite fission-track and (U-Th)/He analyses of basement and cover rocks yield a variety of exhumation ages across major E-W striking structures. (iii) The stratigraphy, petrology, and sedimentological facies of age-equivalent Eocene-Oligocene cover rocks varies significantly across major structures, pointing to abrupt paleoenvironmental changes, convulsive increases in accommodation space, and rapid shifts in sediment provenance and dispersal patterns. (iv) Industrial seismic lines across the Thrace basin fill show ample evidence of strike-slip faulting cutting Eocene to Early Oligocene sedimentary rocks. (v) Large-scale offsets of Bouguer gravity anomaly and crustal thickness.
The concept of Neogene strike-slip faulting in Anatolia as the result of the indentation of Arabia in the Late Miocene should be abandoned, as a mounting body of geological, geophysical, and geodetic data indicate that westward motion of Anatolia was and still is driven by Aegean slab roll-back rather than by the indentation of Arabia. We argue that significant crustal-scale strike-slip tectonism along the North Anatolian and other fault systems such as the Uludag-Eskisehir is an important component of the structural development of western Anatolia at least from the Late Eocene. During Late-Eocene-Oligocene time in NW Anatolia crustal-scale right-lateral strike-slip faults were transporting Anatolian crustal fragments into the N-S extending Aegean domain, thus substantiating further the notion that the westward translation of Turkey ?related to Hellenic slab suction- started earlier than Arabia-Eurasia collision. The collision of the Arabian plate in the Late Miocene might have resulted in the switch of the focus of main strike-slip activity from the Uludag shear zone to the modern North Anatolian fault system.
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