The North Anatolian Shear Zone (Turkey) (2017). geometric, kinematic and age characterization of a crustal scale strike-slip fault

The North Anatolian Shear Zone (NASZ) (Şengör et al., 2005; Ellero et al., 2015) is a major continental strike-slip deformation zone bounding the Anatolian plateau, along the continental collisional zone where the African Plate collides with the Eurasian Plate. Although the NASZ is one of the world’s major active fault system, geometry and kinematics of the tectonic structures associated to the NASZ are relatively little studied and its time-space evolution is still matter of debate. This contribution illustrates the results of a geological-structural field study carried out in the central part of the NASZ in the Kurşunlu-Tosya/Araç-Kastamonu area, where the NASZ overprinted the Intra-Pontide suture zone originated by the middle Paleocene continental collision between Istanbul-Zonguldak and Sakarya terranes, two terrains with Eurasian affinity. In the study area, the NASZ can be considered as a broad up to 30-40 km-wide deformation zone, with a general right-lateral strike-slip deformation distributed along interlinked systems of faults bounding elongated blocks. Overall, the deformation history assumed for the NASZ is characterized by two main tectonic stages showing the switch from left-lateral to right-lateral strike-slip movement associated to the rotation from NNE- to NW- trending maximum stress axis. This evolution model can be applied also for the Taşcilar basin, a pull-apart basin that we have identified inside the NASZ, making a contribution for dating the onset of the NASZ activity. The age of the NASZ activity is commonly inferred from the dating of deposits of the associated pull-apart basins, with a general rejuvenation from east to west, ranging from the late Miocene in the eastern branches of the shear zone, to Pleistocene to the west, in the Marmara Sea region. New biostratigraphic and structural data from the Taşcilar basin suggest an evolution within a strike-slip tectonic regime since the Ypresian, during a first transtensional stage by the activation of releasing step-over areas along left-lateral strike-slip master faults. In a second stage, the rotation of the maximum stress axis re-activates the master faults as dextral strike-slip faults in agreement with the general strike-slip movement of the NASZ. The proposed geodynamic model provides new insights for the timing of the onset of the NASZ activity that is located within the Ypresian, just after the collision between Anatolian and Eurasian plates.