The formation mechanism of duplexes in Kamarhaji Mountain in northwest of Birjand

Duplexes in Kamarhaji Mountain have east-west trend. Duplexes are parallel to the Shekarab fault system. Shekarab fault is a reverse fault with sinistral component that is located in the southern parts of the area. It is considered one of the terminal branches of the Nehbandan fault.Based on Geometric-Kinematic analysis, duplexes are of the horsetail structures types which are located of the side view on each other. There are flower structures in the direction perpendicular to the horsetail structures, that had led the central layer of the duplex structures had maximum height. In duplexes of this region, ramps have strike slip mechanism with thrust component. Existing flats are non-horizontal and most of them have thrust mechanism with strike slip component. Due to the mechanism of flat, transfer direction is to the west side. Since the younger ramp is on the hanging wall of the previous ramp (in other words, younger orientation is into hinterland), the formation model for duplexes is break-back model that examined in the laboratory of Experimental Tectonics. According to the results obtained from different trends of shortening on structures, such as folding and duplexes, the paleostress show two-stage of deformation. Position of strain λ3 axis in the first stage of deformation, according to analysis of the conjugate joints, is N42,00, and according to analysis of joints tension is N40,07 which help axial surface of folding obtained N38,14. Shortening at this stage of deformation is 41.46 percent. Position of strain λ3 axis in the second stage of deformation, according to analysis of the conjugate joints, is N83,02, and according to analysis of the joints tension is N84,00 which help to position the duplexes about N90E. At this stage, strike – slip faults have been further developed, shortening at this stage of deformation is 20.30 percent and the amount of slip along the flats is 2640 meters. According to the geometric-kinematic analysis, duplexes formed during deformation at the second stage that is associated with progressive deformation.