N Naimi-ghassabian; M. M Khatib; T Ghasemi rozveh; H Nazari; M.R Heyhat
Abstract
The Boushad shear zone (BSZ) is situated in the south of Birjand with at least 45 km length, about 9.2 Km width and strike N90E. The parts of the ophiolite mélange shear zone south of Birjand have changed by this shear zone. The earliest deformation, a polyphasesynmetamorphic deformation which ...
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The Boushad shear zone (BSZ) is situated in the south of Birjand with at least 45 km length, about 9.2 Km width and strike N90E. The parts of the ophiolite mélange shear zone south of Birjand have changed by this shear zone. The earliest deformation, a polyphasesynmetamorphic deformation which occurred entirely in ductile conditions, D1 and D2 deformation phases are related to this deformation. The D3 deformation affected the area after a period of sedimentation and erosion, Tension gash veins are formed simultaneously. The Strike-slip faults, thrust faults and fault related folds were classified as structures related to the D4 tectonic event, the most recent phase of conflict in the region N055 ±10E is formed. Degree of convergence of the shear zone is R = 0.3, that indicating the formation of a dextral Transpression (Slightly oblique-convergent).
M.A Alimi; M.M Khatib; KH Hessami Azar; M.R Hayhat
Abstract
An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left-stepping restraining ...
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An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left-stepping restraining stepover. Transpressional deformation in the transverse structure associated with the stepover is expressed as folding and uplifting in the Late Neogene, Quaternary and recent deposits, revealing the Shusf fault as a hidden and blind thrust. Processing of magnetic anomaly maps shows the existence of the Shusf magnetic lineament, which consistently well correlates with the Shusf fault and its hidden segments. Also the hidden part of the fault was investigated by the differential GPS profiles constructed perpendicular to the trend of the Shusf fault scarp. In this study, we used surface morphology surveys, fan median method and satellite images to calculate the cumulative horizontal and vertical offsets related to the Late Quaternary active tectonics along the Shusf fault, measuring mean values of 92 and 4.25 m, respectively. Analysis of the velocity vector recorded in the Nehbandan geodynamic station across the Shusf fault indicates the present-day evolution of the stepover expressed as uplift and left-lateral displacement.
A Rashidi; M.M Khatib; M.R Heyhat; S.M Moussavi
Abstract
In KamarhajiMountain, NW Birjand there are geological structures such as: duplex, pop-Up, triangle zone, flower structures, folding, etc. The duplexes in KamarhajiMountain have E-W trend. They are parallel to the Shekarab fault system. The Shekarab fault is a reverse fault with sinistral component located ...
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In KamarhajiMountain, NW Birjand there are geological structures such as: duplex, pop-Up, triangle zone, flower structures, folding, etc. The duplexes in KamarhajiMountain have E-W trend. They are parallel to the Shekarab fault system. The Shekarab fault is a reverse fault with sinistral component located in the southern of the area; it is considered as one of the terminal branches of the Nehbandan fault. Based on the Geometric-Kinematic analysis, duplexes are of the horsetail structure type, which are set from the side view on each other. There are flower structures in the direction perpendicular to the horsetail structures, caused that the central layers of the duplex structures have the maximum height. Usually in the orogenic regions, the antithetic thrusts with motion opposite to the main thrust are observed. These thrusts are called back thrusts. The hanging wall blocks of two faults, thrust and its back thrust is called pop-Up structure. In addition, in some regions back thrust and new thrust created triangle zone. In duplexes of this Region, ramps have strike slip mechanism with Thrust component. The 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 westward, and since the younger ramps are formed on the hanging wall of previous ramp (In other words, younger orientation is toward the hinterland) the formation of duplexes follows the break-back model. Since the physical model shows a better understanding of the formation model and the relationship between the structures, we have used of the experimental model. The results of experiments show a strong relationship between the geometry of the flat and the geometry of the structures of the area. Based on the paleostress studies and different trends of shortening of structures such as folding, duplexes, two deformational stages were identified. In the first stage, position of strain λ3 axis according to analysis of the conjugate joints, tension joints, and axial surface of folding is N42, 00, N40, 07, and is N38, 14 respectively. The amount of shortening in this stage of deformation is 41.46 %. Position of strain λ3 axis in the second stage of deformation according to analysis of the conjugate joints, tension joints, and E-W trend of thrusts is N83, 02, N84, 00, and N90E respectively. In this stage, strike– slip faults have been further developed. The shortening in this stage of deformation is 20.30 % and the amount of slip along the flats is 2640 meters. According to the geometric-kinematic analysis duplexes formed in the second stage of deformation, which was progressive.
