تاثير نوزمين ساخت بر تحول لندفرم‌هاي دامنه‌هاي جنوب‌غرب شيركوه

An investigation of the Geomorphic evidence of Dehshir fault

مورفوتكتونيك از منظر زمين ساخت و نيروهاي دروني با بررسي چشم اندازهاي هر ناحيه، نقش مهمي در شناخت نحوه تكامل لندفرمها و تفسير آنها دارد. هدف از اين پژوهش بررسي شواهد ژيومورفيك گسل دهشير مي‌باشد. در اين راستا شواهد تكتونيك فعال منطقه با تكنيك هاي مختلف دورسنجي، ژيومورفومتري، پيمايش ها، اندازه‌گيري ها و برداشت هاي ميداني شناسايي و ارتباط فرم و فرآيند مورد تجزيه و تحليل قرارگرفته است. نتايج كمي حاصل از بررسي‌هاي صورت گرفته بر روي تپه شاهدهاي تراورتني (با سن تقريبي 8/1 ميليون سال)، اشكال پلي ژنتيك، پرتگاه‌هاي گسلي و چاه‌هاي اكتشافي منطقه نشان مي‌دهند كه گسل دهشير با جهش تجمعي 200 متري در طي كواترنر، نرخ لغزش تقريبي 11/0 ميلي‌متر در هر سال را داشته است. در واقع اين امر سبب افت سطح اساس شبكه‌هاي زهكشي دامنه‌هاي جنوبغرب شيركوه از اوايل كواترنر تاكنون و در نتيجه تسريع فرسايش قهقرايي و كاوش سطوح تراورتني و پيدايش تپه شاهدها و پيش تپه ها در اين ناحيه شده است. همچنين ديناميك اخير به همراه حركت راستا لغز اين گسل، موجب تغيير شكل شبكه زهكشي، توالي مخروط افكنه ها و ظهور چشمه هاي گسلي شده‌اند كه همگي بيانگر فعاليت قابل توجه اين گسل مي‌باشند.

Introduction: The term morphotectonic or geomorphological tectonic are wed in two different senses:1. tectonic as an instrument for the explanation of landform 2. landform as an instrument for the explanation of tectonic patterns. The first definition implies that we are interested in the landforms themselves-their shape and origins-as functions of tectonic processes. The second definition has a utilitarian value; it allows us to use geomorphology as a tool to evaluate the history, magnitude, and rate of tectonic processes. Here, morphotectonic has turned into a major instrument in identifying active faults, understanding the structural evolution of geology, evaluating seismic risks and studying landscape evolution (Keller & Pinter, 2002). Dehshir fault with a length of approximately 350 km is considered as an important structural element in the south of central Iran. Through the identification and analysis at active tectonic evidence at the area, the present study attempts to determine 1) The tectonic performance at the above-mentioned fault on quaternary landforms and 2) The amount of landform movement during the quaternary. So as to find out how landforms evolved in this area. Methodology This study and the morphotectonic investigation at the area began by limiting the () to be studied through digital elevation model. Then through 1/100000 geology maps, the area faults were identified and completed with a high resolution by making use of pictures in the next stage, morphotectonic evidence was extracted through telemetry, geomorphometry and field investigations. Afterwards this evidence was analyzed to identify the tectonic rale. The height of cliffs fault (vertical jump) was determined through 10 meter DEM at the studied area and considering the initial slope at the earth by drawing some particles (superimposed)The succession at cones was segregated through satellite pictures, field studies and using criteria such as: the difference between the texture at particles, material orientation, relative height, reflex (on pictures) and erosion pattern. To identify the amount of vertical movements of Dehshir fault the deviation of canals was measured through satellite pictures and field operation. In the next stage of field study, polygenic shapes wich are a piece of evidence far active tectonic in the area were examined. () addition, to analyse () of of the southeast hillsides of Shir Kooh the materials of these hills and their changes during the quaternary was examined and its height was compared with the amount of movement in Dehshir fault. Results: One of the morphotectonic evidences at the area is the cliff fault which, based on the drawn altitudinal particles on travertines of hanging walls and foot walls of Dehshir fault, was calculated to be 200 meters overall (around ? 0.11mm per year). Bar vegetation is among the morphotectonic evidence at the area. In addition 3 successions at cones was identified in the east of Abar Kouh. Drainage networks have been derived about 55 to 170 meters. The desert sediments are located far away from the present level of Abar Kouh desert. Discussion and conclusion: Dehshir, Shahrebabak and Touran Posht faultas have changed the quaternary landforms of the studied area. The amount of altitudinal difference caused by Dehshir fault was calculated through drawing 200 meter superimposed profiles (cumulatively) which was ? 0.11mm per year. The exploratory well of regional water authority can also confirm this altitudinal difference. Foroutan et alʹs. (2009) study is one of the investigations carried out of Dehshir fault which examined the slop tone of this fault throng luminescence light method. They stated that the annual slip tone of the horizontal factor of the fault in the investigated period (the late pleistocene-holocene) is 1±0.3 mm yr-1 and for the vertical factor is around 0.1 mm yr-1. The presence of 3 successions at cones in the east of Abarkooh suggests a continual reduction in the basic level of Abarkooh desert due to Dehshir fault and the activity of Shahr-e-Babak fault. The most amount of deviation of canals in the studied area is after the formation of canals. This amount can be equal to the deviation of canals which Foroutan et al. measured in Marvast cones (50-185). The existence of polygenic C shapes for away from the present location shows the subsidence of Abarkooh desert in the quaternary. The travertine () are with an approximate height at 200 meters are the most prominent landforms created by the faults which can be approximated to the height of Cliff faults which is 200 meters. In fact, such an altitudinal difference has resulted in regressive erosion and the formation of Butte. Overall, based on investigations it can be concluded that Dehshir fault has a high seismic potential.