Oblique to Orthogonal Convergence Across the Turan Block in the Post-Miocene

Abstract

The 2-17-km-thick, post-Triassic sediments of the Turan continental block accumulated in a south-dipping basin characterized by fault-controlled facies and thickness variations. Since the late Miocene, the thickest part of the basin fill, on the southern margin of the Turan block, has been folded and uplifted as the Kopet Dag range, in response to the Iran-Turan convergence. The Apsheron sill, which separates the northern continental from the southern oceanic Caspian Sea basins, links the Kopet Dag-Greater Balkan ranges (Turkmenistan) to the Caucasus (Azerbaijan). The large-scale east-west- to west-northwest-east-southeast-oriented arrays of periclinal folds of the Kopet Dag range, which indicate a north-south oriented compression, were generated by a fault propagation mechanism. The migration and accumulation of hydrocarbons has been controlled by the deformation pattern. The 75 km of north-south shortening in the western Kopet Dag-Greater Balkan area can be resolved into 70 km of pure compression, orthogonal to the N120°-oriented Ashgabat fault, and 35 km of dextral slip along this fault. The north-south Iran-Asia relative motion has produced the oblique convergent northwest-southeast structures along the dextral Ashgabat fault and the pure convergent east-west structures in the western Kopet Dag-Greater Balkan region. The orientation of the structures has been controlled by the angular relationship between the relative motion of two blocks and the orientation of their boundaries. The Ashgabat fault as a major crustal anisotropy has concentrated the deformation into a narrow fold and thrust belt, whereas in the west the deformation is distributed over a wider area. The pattern of deformation has been controlled by the Iran-Turan boundary conditions.