Post-collisional deformation of the Anatolides and motion of the Arabian indenter: A paleomagnetic analysis

Abstract

In the Anatolides of Turkey the neotectonic (post collisional) phase of deformation embraces the period since final closure of the southern arm of Neotethys in mid-Miocene times. The Arabian Shield indenter has continued to deform into the weak Anatolian accretionary collage resulting from subduction of this ocean by a combination of differential movement relative to the African Plate and counterclockwise (CCW) rotation. Much of resulting deformation has been accommodated by slip along major transforms comprising the North Anatolian Fault Zone (NAFZ), the East Anatolian Fault Zone (EAFZ) and the northward extension of the Dead Sea Fault Zone (DSFZ) but has also been distributed as differential block rotations through the zone of weak crust in between. Facets of this deformation comprise crustal thickening and uplift to produce the Anatolian Plateau, establishment of transform faults and tectonic escape as Arabia has continued to impinge into the Anatolian collage. Paleomagnetic analysis of this deformation is facilitated by the widespread distribution of neotectonic volcanism and graben infills, and rotations relative to the Eurasian reference frame are recognised on two scales. Rapid rotation (up to 5°/10,000 years) of small fault blocks is identified between master faults along the intracontinental transforms but deformation does not extend away from these zones and shows that seismogenic upper crust is decoupled from a lower continental lithosphere undergoing continuum deformation. The broad area of weak accreted crust between the transforms is dissected into large fault blocks which exhibit much lower rotation rates (mostly < 1°/100,000 years) that vary systematically across the Anatolides. Large CCW rotations near the Arabian indenter diminish westwards to become zero then CW near the limit of tectonic escape in western Turkey. The view that the collage has rotated anticlockwise as a single plate, either uniformly or episodically, during the Neotectonic era is refuted. Instead, deformation has been distributed and differential as the collage has adapted to changing tectonic regimes. Crustal extrusion to the west and south has expanded the curvature of the Tauride Arc and combined with retreat of the Hellenic Arc to produce the extensional horst and graben province in western Turkey. A challenge of present work is to resolve the temporal framework of tectonic rotation. Evidence from the Cappadocian volcanic province and Sivas Basin in central Anatolia indicates that rotation has been concentrated within the last 2–3 million years of the neotectonic era and therefore correlates with establishment of the intracontinental transform framework. Thus we recognise two phases to the evolution of this sector of the orogen: the first embraces crustal thickening and uplift with initiation defined specifically by transition from marine to terrestrial deposition in the Serravallian at ~12 Ma, and the second embraces crustal extrusion to the west motivated by continuing northward movement of Arabia and roll back on the Hellenic Arc since late Pliocene times. Latitudinal motions detected by paleomagnetism are close to confidence limits and consistent with small northward motion of the Anatolides since Eocene times including up to a few hundred km of closure linked to crustal thickening since the demise of NeoTethys. The driving motion from the Arabian indenter can be partially resolved from the widespread basaltic volcanism that occurred along the periphery of the Arabian Shield at 12–18 Ma during final stages of collision along the Bitlis Suture. This defines CCW rotation of 13–21° with respect to Eurasia. An average CCW rotation of 0.9°/Myr since closure of the Bitlis Suture in mid-Miocene times is unlikely to have been uniform because it has been linked to three adjoining interactions namely episodic opening of the Red Sea, a transition from crustal thickening to tectonic escape in the Anatolian collage and variable rates of strike slip motion on the DSFZ.