Distributed neotectonic deformation in the Anatolides of Turkey: A palaeomagnetic analysis

Abstract

The palaeotectonic phase of deformation in Anatolia accompanied closure of the Tethyan Ocean and was finally completed with sealing of the Bitlis Suture bordering the Arabian Shield at similar to 12 Ma. Arabia has since continued to indent the collage of terranes accreted to the Eurasian margin by differential northward movement relative to Africa along the Dead Sea Fault Zone and counterclockwise (CCW) rotation accompanying the opening of the Red Sea. This neotectonic phase of deformation has accompanied uplift of the Anatolian Plateau and establishment of intracontinental transforms comprising the North and East Anatolian Fault zones. Deformation has included extrusion and rotation of blocks away from the Arabian Syntaxis by tectonic escape. We produce an updated summary of palaeomagnetic results from this region to show that deformation has been distributed so that block rotations vary systematically across Anatolia ranging from strongly CCW in the zone of high strain north of the Arabian indenter to near zero in central Anatolia and then progressively CW in western Anatolia. New palaeomagnetic results from the Ankara igneous district are also reported and help to constrain the east to west change from CCW to CW rotation within central Anatolia. The transition of tectonic regimes from compression in the east to extension in the west involves the expulsion of blocks and their rotation along arcuate strike slip faults at an acute angle to the maximum compressive stress (sigma(1)) between Arabia and Eurasia. The comparable distribution of rotations in palaeotectonic and neotectonic units indicates that the bulk of the observed palaeomagnetic rotations have been concentrated within the last (Plio-Pleistocene) phase of the neotectonic era as is found in the Aegean domain to the west, and has involved blocks of the order of similar to 100 km in size. The weak collage of accretionary terranes "sandwiched" between the Arabian Indenter and the Eurasian margin, now defined by the North Anatolian Fault Zone, has evidently taken up the bulk of the strain imparted by the continuing northward motion of Arabia to expand the radius of the Tauride Arc and the perimeter of extruded crust bordering the limit of the extensional province in western Turkey. The distributed character of neotectonic deformation is illustrated by equivalent polar distributions: both palaeotectonic and neotectonic palaeomagnetic poles show arcuate distributions with poles to best-fitting small circles focussed close to the study area. Differences between the distributed neotectonic deformation resolved from palaeomagnetism and the contemporary GPS record reflect the contrasting time periods being evaluated: the palaeomagnetic record incorporates evolving and changing tectonic regimes whereas the GPS signature has no long term validity within the weak Anatolian collage; hence the full spectrum of techniques for resolving neotectonic deformation is relevant to unravelling deformation in such regions. (C) 2009 Elsevier B.V. All rights reserved.