New constraints on tectonic inversion–based Orogeny of Western Kopet-dagh (NE of Iran)

Abstract

One of the orogen types in the intra-continental tectonic settings is pop-up structures with bi-vergent thrust tectonics. In this research, the western part of the Kopet-dagh Orogen, as the southern boundary of the Turan Plate, is selected as a case study for investigation on tectonic development and deformation patterns, using surface–subsurface structural studies together with complementary remote sensing and GIS environmental capability as a multi-disciplinary approach. The results of this research determined two sets of faults, consisting of (a) first-stage longitudinal reverse faults with a structural trend of N90–100 to N50–70 (Tangrah, Takal-Kuh, Marave-Tappe, and Golijeh faults), and (b) transversal right-hand strike-slip faults with a trend of N130–150 (Kalaleh, Ughcheh, and Sarighamish faults). These two sets of faults formed the structural framework of this zone and played an important role in the tectonic evolution (initiation, shaping, evolution of sedimentary basins, and forming a fold-thrust belt) of this orogen. A change in the mechanism of the first-stage longitudinal faults, as tectonic inversion, at the onset of the Late Alpine Orogeny caused the re-arrangement of P-axes and thus formed bi-vergent reverse faulting in the northern and southern edges of this zone. Subsequently, fault propagation folds were established due to this event. Finally, an extensive V-shaped compressional pop-up structure with bi-vergent thrusting and fold axial surfaces (as fault-related folds) was formed in the Kopet-dagh fold-thrust belt. Also, the mechanism of the second-stage transversal faults changed to right-hand strike-slip faults with some normal components at the onset of the Late Alpine Orogeny. The normal component of these faults (especially the Kalaleh fault) caused the settlement of the western part of this zone along them and formed the Gorgan-Gonbad plain.

Graphical abstract