MARMARA BASINS ARE STRIKE-SLIP: EVIDENCE FROM THE 52±1 KM TOTAL OFFSET OF THE NORTH ANATOLIAN FAULT IN NORTHWEST TURKEY

Along the western part of the North Anatolian Fault zone, estimates of the cumulative offset range between 4 km to 85 km. These different estimates also lead to different interpretations on the formation of Marmara Basins. The Marmara Basins interpreted either as pre-strike-slip extensional basins cut by the North Anatolian Fault, or strike-slip basins formed through the activity of North Anatolian Fault. In this study we use Cretaceous faults sub-perpendicular to the North Anatolian Fault as precise offset markers. Based on these faults, as well as the offset of the Eocene volcanic belts, the cumulative dextral displacement along the main strand of the North Anatolian Fault is measured as 52 ± 1 km in the eastern Marmara region. With an assumed 20 mm yr^-1 average slip rate, the 52 ± 1 km offset along the North Anatolian Fault indicates an inception age for the transform in the Pliocene between 3.5 Ma and 2.6 Ma in the Marmara region. This displacement along the North Anatolian Fault is sufficient to open the Marmara Basins as transtensional structures. Therefore, the Marmara Basins are not pre-transform but have formed during the activity of the North Anatolian Fault.