NEOTECTONICS OF A STRIKE-SLIP RESTRAINING BEND SYSTEM, JAMAICA

Abstract

Abstract Strike slip on various scales and on faults of diverse orientations is one of the most prominent modes of deformation in continental convergence zones. Extreme heterogeneity and low shear strength of continental rocks are responsible for creating complex “escape routes” from nodes of constriction along irregular collision fronts toward free faces formed by subduction zones. The origin of this process is poorly understood. The two main models ascribe tectonic escape to buoyancy forces resulting from differences in crustal thickness generated by collision and to forces applied to the boundaries of the escaping wedges. Escape tectonics also creates a complicated geological signature, whose recognition in fossil examples may be difficult. In this paper we examine the Neogene to present tectonic escape-dominated evolution of Turkey both to test the models devised to account for tectonic escape and to develop criteria by which fossil escape systems may be recognized. Since the late Serravallian (—12 Ma), the tectonics of Turkey has been dominated by the westward escape of an Anatolian block (“schölle”) from the east Anatolian convergent zone onto the oceanic lithosphère of the Eastern Mediterranean Sea, mainly along the North and East Anatolian strike-slip faults. This tectonic regime generated four distinct neotectonic provinces: (1) The East Anatolian contractional province, located mainly east of where the North and East Anatolian faults meet, and characterized by roughly north-south shortening; (2) the weakly active North Turkish province situated north of the North Anatolian fault, and characterized by limited east-west shortening; (3) the West Anatolian extensional province characterized by north-south extension; and (4) the Central Anatolian “ova” province characterized by northeast-southwest shortening and northwest-southeast extension. Large, roughly equant, complex basins ( “ovas” ) form peculiar structural elements of the Central Anatolian province. The two latter provinces are located within the westerly-moving Anatolian schölle. A number of pull-apart and fault-wedge basins have formed along the North and East Anatolian fault zones in addition to several other “incompatibility basins,” arising from space problems where these faults interfere with each other and with other large-scale structures. Incompatibility basins seem to have the most complicated structural history. The pull-apart basins are located on either primary or secondary releasing bends along the North and East Anatolian faults. The secondary type is related to the intersection of east-trending zones of high convergent strain with the North and East Anatolian fault zones. The tectonic escape regime in and around Turkey was not caused by buoyancy forces resulting from crustal thickness differences, but such forces may have been maintaining it. A knowledge of the geology of escape-related basins is critical both for our understanding of the nature of tectonic escape, and for its recognition in the geological record. We believe that the present tectonic scheme of Turkey constitutes an excellent guide for understanding the causes and consequences of escape, and for the recognition of its fossil representatives.