Structural style and kinematic analysis of the northern Birjand Mountain range, Sistan suture zone, Eastern Iran

چکیده مقاله

Abstract The Sistan suture zone comprises the boundary between Lut and Afghan blocks. The north-south shear between Iran and Afghanistan is accommodated by several right-lateral strike-slip fault systems. The study area (northern Birjand Mountain range) is a part of Khousf splay; the most important faults in the Khousf splay are sinistral with reverse component and thrust with sinistral component faults; the Khousf splay is a sinistral transpressional zone including shear folds, pop-ups, positive flower structures, and duplexes. In this research, we used field data including geometric and kinematic characteristics of the faults to determine the structural deformation model of the northern Birjand Mountain range. In the northern Birjand Mountain range, several ~E-W striking faults cut through geological units; geometric and kinematic analyses of these faults indicate that almost faults have reverse components which reveal existing of compressional stress in the study area. The northern Birjand Mountain range has been characterized by main reverse faults with ~E-W striking faults. Moreover, most of the faults in the Khousf splay are thrust with left-lateral components, which were activated as a result of the NE-SW direction stress regime. The Khousf splay is a sinistral shear zone, and the beginning of deformation in this splay is from east to west. Structural analysis in the study area indicates that the F1 and F2 reverse faults have southward dips and F3 and F4 reverse faults have northward dips. Investigating the faults in the northern Birjand Mountain range implies that these reverse faults join the Nehbandan fault system. The Nehbandan fault system has splays in the Northern and Southern terminals, and the northern terminals of the Nehbandan fault are reverse faults with nearly E-W striking. The main reverse faults of the study area include F1 to F4 faults which are continuations of the Nehbandan fault system. Therefore, the kinematics and geometry of these faults in the northern Birjand Mountain range suggest pop-up and positive flower structures in a sinistral transpressional zone.