Tectonic evolution of the Niksar and Tasova-Erbaa pull-apart basins, North Anatolian fault zone: Their significance for the motion of the Anatolian block

The Tasova-Erbaa and Niksar basins are two adjacent pull-apart basins along the North Anatolian Fault Zone (NAFZ). Within the Tasova-Erbaa basin, sedimentary lithofacies of the Upper Pontus Formation (Plio-Pleistocene) are asymmetrically distributed, with laterally derived alluvial fans, coarse braid plain deposits, and axial braided stream deposits dominating the northern and western parts of the basin. The basin has gently dipping sediments locally affected by pervasive extensional (T) faulting. Isolated compressional structures are associated with master faults (deformation zone width ≤ 500 m). Pervasive extensional faults (T and R?) and late-stage PDZ-parallel compressional faults are also present. An additional set of extensional faults trends perpendicular to the PDZ, accommodating secondary pull-apart stretching within the basin. The distribution of sedimentary facies and structural styles is consistent with that predicted by models for pull-apart basins. The adjacent Niksar basin is an active pull-apart basin, possibly as young as 0.5-1 Ma. Its modern drainage and sedimentary facies are symmetrically arranged. Adding the lengths of the Tasova-Erbaa and Niksar basin suggests ~ 80 km total displacement along the North Anatolian fault, which is consistent with Seymen (ITU Ph.D. Thesis, 1975), Sengor [J. Geol. Soc. 136 (1979) 269-282] and Armijo et al. [Tectonophysics 243 (1999) 135-154], who observed about 85 ± 5 km total displacement along the North Anatolian fault. The change in course of the North Anatolian fault, marked by the formation of the Niksar-Ezinepazari segment, and this new geometry suggest that the Anatolian block is rotating anticlockwise by having two separate poles: one located near Damascus and the other occurring north of the Sinai peninsula. This change may also mark the transfer of the Anatolian triple junction from Erzincan to Karliova about 1 Ma ago. Furthermore, it appears that while the fault shortcuts the older basin, a new generation of pull-apart basins are formed due to changes of boundary conditions along the fault zone. (C) 2000 Elsevier Science B.V. All rights reserved.