Neotectonic deformation in the Eurasia–Arabia collision zone, the East Anatolian Plateau, E Turkey: evidence from palaeomagnetic study of Neogene–Quaternary volcanic rocks

Palaeomagnetic studies of the Neogene–Quaternary rocks of Anatolia have been mostly interpreted in the light of its westward escape as a result of the collision between the Arabian and Eurasian plates along the Bitlis–Zağros suture during the Neotectonic period. However, within the collision zone, in East Anatolia, palaeomagnetic data are not available. In order to help understand the deformational history of Eastern Anatolia during the Neotectonic period, we have carried out a palaeomagnetic study of Miocene–Quaternary volcanic rocks from 100 sites, selected on the basis of their geographical position and known age. The results indicate that the study area can be divided into five principal tectonic blocks, based on earthquake activity and the rotation that the blocks underwent. These blocks are the Van Block (VB), the Kars Block (KB), the Anatolian Block (AB), the Pontide Block (PB), and the Arabian Block (ARB). The largest counterclockwise (CCW) tectonic rotations were encountered in the AB and PB, whereas the largest clockwise (CW) rotations were recorded in the VB. The sinistral East Anatolian Fault and the Erzurum Fault Zone form the present boundary of these two contrasting, CW and CCW-rotating domains. Both the AB and the PB exhibit similar amount of rotation until the Quaternary, during which the AB rotated 13° CCW while the PB remained stable. The Quaternary rotation of the AB is attributed to the activity of the North Anatolian Fault. The KB shows the smallest amount of CW rotation during all of the time intervals studied. All of the blocks studied indicate an acceleration in the amount of rotations during the Quaternary, which was preceded by a period of relative tectonic stability during the Late Pliocene. Following the collision of the Arabian Plate with the Eurasian Plate during the Mid-Miocene, the crust was initially thickened by thrusting and folding. This was followed by lateral extrusion and differential rotation of the crustal blocks during Late Miocene–Pliocene in response to ongoing indentation of the Arabian Plate. Our data show that strike-slip faults that commonly separate wedge-shape crustal blocks are the most significant means of accommodating the tectonic escape and rotation of crustal blocks in East Anatolia. Delamination of the lower crust and the lithospheric mantle may have contributed to the deformation by thermally weakening the crust.