121 Afkhami Ardakani et al. / Iranian Journal of Earth Sciences 10 (2018) / 121-134 Islamic Azad University Mashhad Branch Geometric and kinematic analysis of Dorbadam anticline, North of Quchan, Iran Hamidreza Afkhami Ardakani1, Farzin Ghaemi*2, Behnam Rahimi2 1. Master of Tectonics, Department of Geology, Ferdowsi university of Mashhad, Iran. 2. Department of Geology, Ferdowsi university of Mashhad, Iran. Received 24 May 2017; accepted 5 January 2018 Abstract The geometric and kinematic analyzing of the anticlines and their relation with the large-scale structures are used to determine the structural evolution of the area. The Dorbadam anticline is located in the Kopet-Dagh structural zone, 45 km due north of Quchan and on the Razavi and North Khorasan provinces border. The field study and geometric analysis indicate that the Dorbadam anticline has two culminations with an en-echelon arrangement and different structural evolution. The NW culmination (DA.1) is analyzed as a fault propagation fold geometry, while the SE culmination is known as a simple folding. The axial trend of the Dorbadam anticline has been changed and shows harmonic and Horizontal inclined, 1C subclass of Ramsay's classification, close, asymmetrical over fold in DA.1 part; upright and horizontal, open and symmetrical upright fold in DA.2 part. Aspect ratio on the Dorbadam anticline is 0.64 and has a parabolic appearance. The joint study revealed the existence of five major joints in this area which are bedding and strike joints (tension and compression joints parallel to the axial fold) or dipping joints (tension joints). The systematic joints analyzing of Tirgan Formation with T-Tecto software determined that the trend of maximum stress in the Cretaceous was S07W. The paleo-stress direction determined S25W with axial plane analysis. The Analysis of large-scale faults indicated a change in the stress direction during the time and specified they are post-tectonic and the activity of faults occurred in some various stress systems. Keywords: Dorbadam anticline, Kopet-Dag, Tirgan Formation 1. Introduction The Kopet-Dagh is a fold-thrust belt with NW-SE trend, of the Kopet-Dagh has been associated with the which forms the northern border of the Alpine- development of thrust faults and folding in some parts. Himalayan system on the Iranian plateau. The Kopet But thrust faults are less seen on the surface. The Dag basin has been formed after the Cimmerian orogeny Dorbadam anticline with the strike of NW- SE and (Berberian and King 1981; Zanchetta et al. 2013), and overturned limb in some parts of the northern limb and post-Miocene pressure deformations have caused the due to the general stresses of the area can be folding in folding and uplift of the basin sediments and forming connection with fault in depth. On the other hand, the the structures of the anticline and syncline. (Lyberis et existence of a small anticline with a different axial trace, al. 1998; Shabanian et al. 2010; Javidfakhr et al. 2011). in the northern limb of the main anticline, can reveal Geologically, the Kopet-Dagh Range is made chiefly of changing the trend of stress in the studied area, which Lower Cretaceous sedimentary rocks with a smaller shows the importance of studying this area. With using portion of Jurassic rocks in the southeastern parts. The previous studies in the area, studying maps and aerial mountains were formed in the Miocene and the Pliocene photographs and data taken from field surveys, during the Alpine orogeny (Afshar Harb et al. 1987; investigating faults and fractures, and using software Afshar Harb 1994; Navabpour et al. 2003; such as Stereo net and etc. analyze this region Sheikholeslami et al. 2013; Afkhami Ardakani et al. geometrically and dynamically. 2017). The study area in this research is Dorbadam anticlinal in 45 km due north of Quchan city and is 2. Kinematics of area located on the border between two provinces of The tectonic shortening applied to the north-east of Iran Khorasan Razavi and Northern Khorasan. This area is in in the Kopet Dag basin appears in various forms. From the Kopet-Dagh Structural zone in between 37° 21´ - this perspective, the basin can be divided into three 37° 32´ North latitude and 58° 10´ - 58° 41´ East parts: eastern, middle, and west. In the eastern part, the longitude. The village of Dorbadam is limited from the North-South shortening is conforming with the thrust north to Bajgiran, from the south to Quchan, from the faulting. In the middle section, it shows North-South east to Darehgaz and from west to Shirvan (Fig 1). The shortening and East-West extension. By turning deformation of the sedimentary cover in the folded belt counterclockwise, the blocks are limited to the Quchan --------------------- fault zone, and we can see escape of the west part of the *Corresponding author. Kopet-Dagh towards the west near the Caspian Basin E-mail address (es): [email protected] (Fig 2a, b) (Hollingsworth et al. 2006, 2008). Afkhami Ardakani et al. / Iranian Journal of Earth Sciences 10 (2018) / 121-134 122 Fig 1. Geographic location of the study area in NE of Iran. Dorbadam anticline is shown with yellow line. Satellite photo from Google Earth. 3. Geometric analysis topographic slope, on the northern limb of the anticline 3.1. Structural geometry of the Dorbadam anticline relative to the South limb, is a confirmation of the The great anticline of Dorbadam with the general trend northern limb reversal. of NW-SE, is located in the Distance of 45 km from In the northwestern part of the Dorbadam anticlinal Quchan and north of the anticline of Imam Gholi (Fig 1) (DA-1) and in the geographical position 37° 30´ 35/80 This anticline is about 50 km long with doubly hump and 58° 23´ 50/1 there is a thrust fault that causes the (DA.1, DA.2) and has a z-shaped axial trace (Fig 3). formation of the S-C structures (Fig 6a). As a result, The axial plane of the segment DA.1 has a curved shear sense of area in which this texture is located is geometry and is approximately 25 kilometers long and proposed here, which suggests a thrust mechanism for varies from 0.5 to 2 kilometers in width. Field the fault in which the shear zone is located. In this observations indicate that the northern limb of DA.1 has section, the fault mirror with a profile of 125.45 was reversal and the Tirgan Formation units are sloping taken, which confirms the line of scratch on it with a towards the south along this limb (Fig 4). rake angle of about 90 degrees (Fig 6b). In the transverse profiles of the Northwest segment The anticline formation and reversal of the northern (DA.1) of the anticline (A-A ', B-B', C-C ') (Fig 5), the limb of anticline in this section are controlled by the 123 Afkhami Ardakani et al. / Iranian Journal of Earth Sciences 10 (2018) / 121-134 growth of a fault in the anticline core and we can see the limbs in both sections DA.1 and DA.2. In the fault propagation fold in this part of the anticline. Since northwestern part (DA.1), the axial plane has 59 folding has occurred in the competent layers of degrees’ slope and a 28-degree plunge of fold axis (Fig limestone of Tirgan formation, with the growth of 8a). According to the Fleuty classification, this part of folding, locking and stress accumulation in the anticline the anticline is Moderately inclined and Gently plunging occurred, and due to the greater focus of the fractures in fold, and is collectively called the Horizontal inclined the area of the Hinged plane region, along with the fault fold. In the south east of the anticline (DA.2), the axial occurred. So the movement has occurred on the fault plane has a slope of 89 degrees and the fold axis has a and caused the growth of folding. Thus, the Dorbadam plunging of about 8 degrees (Fig 8b). According to the anticline in the DA.1 segment has been an anticlinal Fleuty classification, this section of the anticline is breakthrough (Suppe 1983, 1985; Suppe and upright and horizontal fold. Medwedeff 1990; McClay 2003) (Fig 7). Another way of fold classification is based on the appearance of folds in its profile (Ramsay 1967). In a 3.2. Geometric Parameters of Dorbadam anticline cross section of the Dorbadam anticline in the village of One of the ways to classify the folds is based on the Dorbadam, a geometric drawing was done on two properties of axial surface and the hinge line. In this folded layers of Tirgan Formation and Measured the method, we first refer to the axial plane slope and then parameters to, tα and Tα (Fig 9) and t'α were calculated to the Plunge of hinge line of the fold. Since the two (Table 1), which is equal to 0.83 and, due to the slope of sections of the anticline have different structural event, the axial plane in this section (59 degrees), Dorbadam they should be studied separately. In order to calculate anticline in the DA.1 section is in the 1C class of the axial plane of fold, field observations were made Ramsey classification. from the direction and slope of the layering of fold’s Fig 2. a) Northeast Iran topography map with simplified tectonic model. In the western part of the 59-degree longitude, the north- south convergence of Iran-Eurasia plates is being driven by strike slip movements on the Ashgabat and Shahrood fault systems. The Bakharden-Quchan fault zone accommodates the North-South shortening and East-West traction by counterclockwise rotation of a set of blocks.