ارزیابی و کارایی تکتونیک فعال شمال غرب صحنه با استفاده از شاخص های مورفوتکتونیک (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
منطقه مورد مطالعه در شمال غرب شهرستان صحنه و از نظر زمین شناسی در پهنه زمین درز کوهزایی زاگرس یعنی مرز پهنه سنندج سیرجان و زاگرس مرتفع قرار دارد. در این منطقه واحدهای سنگ شناسی مختلفی از جمله افیولیت ملانژ میانراهان شامل گابرو و بازالت های بالشی و همچنین سنگ های آهکی رخنمون دارند. گسل های فراوانی با سازوکارهای مختلف در این منطقه شکل گرفته اند که از مهمترین آن ها می توان به گسل جوان زاگرس و گسل رورانده زاگرس اشاره کرد. در این پژوهش برای بررسی ریخت زمین ساخت منطقه، شاخص های متعددی از جمله شاخص عدم تقارن حوضه زهکشی (AF)، شاخص تقارن توپوگرافی عرضی (T)، شاخص انتگرال هیپسومتری (HI) و منحنی انتگرال هیپسومتری (Hc) ، شاخص گرادیان طولی آبراهه یا شیب جریان – طول رود (SL)، شاخص نسبت شکل حوضه زهکشی (BS)، شاخص نسبت طول حوضه زهکشی به میانگین عرض آن حوضه (Bl/Bmw) و شاخص دامنه ناهمواری (RA) مورد تحلیل و بررسی قرار گرفتند. بررسی زمین ساخت فعال نسبی (IAT) با استفاده از شاخص های فوق نشان می دهد که منطقه از فعالیت نسبی متوسط (اغلب حوضه ها) تا زیاد (حوضه های 1،16،17،18،22،23) برخوردار است. بررسی دقیق شاخص ها این موضوع را نشان می دهد که در حوضه هایی که گسل های راندگی از آن عبور کرده اند، کج شدگی و عدم تقارن حوضه ها رخ داده است. همچنین در جنوب شرق منطقه که گسل صحنه و گسل رورانده زاگرس بهم پیوسته اند شاخص گرادیان طولی رود بیشترین مقدار را نشان می دهد. نکته قابل توجه دیگر این است که در بخش هایی که گسل امتدادلغز صحنه عبور کرده است، جابجایی آبراهه ها رخ داده است که شواهد این جابجایی در عکس های هوایی و یا تصاویر ماهواره ای به خوبی قابل تشخیص و اندازه گیری است. مقدار جابجایی آبراهه ها، در این منطقه بیش از 2.5 کیلومتر برآورد شده است.The Evaluation and efficiency of active tectonics in the northwest of the Sahneh using morphotectonic indicators
IntroductionThe studied area is located in the northwest of Sahneh city. The oldest variety of lithology in this area is related to the Mesozoic era and the Triassic, Jurassic and Cretaceous periods. Among the most important outcrops related to this period, we can mention the Biston limestone of Triassic-Upper Cretaceous age, Kermanshah radiolarites of Upper Jurassic-Lower Cretaceous age, as well as older Triassic rocks such as schist and marble. A huge part of the region has been affected by various types of faults such as thrust and reverse faults, normal faults and strike-slip faults. It is important to note that most of the faults in the region are of thrust or reverse type, which have sometimes caused the formation of a duplex structure in the area. Probably, these thrust and reverse faults have a greater role in creating the active tectonics of the region than strike-slip faults.MethodologyIn order to investigate and analyze the morphotectonics of the study area, first the geological and topographical maps of the area were examined, then by using a digital elevation model with an accuracy of 10 meters (DEM), basins and drainages were extracted in the ArcGIS 10.8 software environment with the Arc Hydro extension.Then, by using Google Earth Pro software, the necessary corrections and proper basin were extracted from ArcGIS 10.8 software. In this research, in order to calculate the morphotectonic index, the study area has been divided into 23 drainage basins.Results and Discussion In the following, the introduction and analysis related to each index will be discussed.Drainage basin symmetry factor (AF)This index indicates the degree of tectonic tilting of the basin in relation to the main drainage and must necessarily be perpendicular to the main drainage. In this index, the amount of rise and fall on both sides of the basin (right and left side of the main drainage) is of particular importance. Transverse topographic symmetry (T)This index has been introduced to evaluate a river within the basin, which examines the amount of changes related to the asymmetry of that river in different parts of the valley. The calculated numerical value is between zero and one, and the closer this number is to one, it means that uplift has occurred on one side of the basin, and as a result, the degree of tilting is also increasing, and the basin is moving towards asymmetry and active tectonics.hypsometric curve(HC) and Hypsometric integral (HI)This index represents the distribution and dispersion of the height in a particular drainage basin, and the erosion and instability of the slopes are considered important factors in changing the height of the basin. Altimeter curve is a two-dimensional curve. According to the Hypsometric curves of each basin, it can be concluded that in almost all basins, the youth phase is ending due to factors such as erosion and the decrease in the height of the slopes, and the maturity phase is more visible in most of the basins. Stream length - gradient index (SL)This index is to investigate the active tectonics regarding the role of the river channel and the resistance of the rocks of the study area. Based on this index, three types of basins can be introduced in such a way that if the numerical value of this index decreases from upstream to downstream, that is, the slope of the waterway decreases from upstream to downstream, the basin has a low elevation. If the numerical value of this index is increasing from upstream to downstream, it means that the slope is increasing from upstream to downstream, so the elevation of the basin is high, and if the numerical value of this index is fluctuating from upstream to downstream, is an indication of the average elevation in the basin. Drainage basin shape index (BS)This index refers to the study of the elongation of the basin. In this way, the more elongated the basin is, it indicates more tectonic activity in that basin, and vice versa, when the tectonic activity decreases or stops, as a result, erosion will overcome the basin and as a result, the basin will lose its elongation over time. and finally the circular basin is formed. The calculations of this index show that most of the basins are Inactive category. But According to Bl/Bmw index calculations, a number of basins are in active and semi-active category. Relief amplitude (RA)This index is between the highest height (maximum) and the lowest height (minimum) of the drainage basin, which is evaluated and is one of the parameters used to evaluate the level of activity of an active tectonic basin. Relative index of active tectonics (IAT)This index represents an average of the tectonic activities of each basin compared to the all measured indices. This index is also divided into 4 categories, respectively, category 1 means very high tectonic activity (1.0≤IAT<1.5), high tectonic activity (1.5≤IAT<2.0), moderate tectonic activity (2.0≤IAT<2.5) and low tectonic activity (IAT≥2.5). ConclusionThe northwest of Sahneh city is located in the most dynamic part of Zagros orogeny. In this area, all typs of thrust, normal and strike-slip faults can be observed. The Sahneh fault as the middle part of the Zagros recent fault passes exactly through the central part of the region. There are many thrust faults in the region, including the Main Zagros Reverse fault. The Sahneh fault and the Main Zagros Reverse fault are far apart in this area, but they connect to each other in the southeastern part of the area. The connection of these faults has caused tectonic activity in this area, which shows this well in the measurement of the SL index. The effect of thrust faults can be clearly seen in other indexs, which have caused the tilting of sedimentary basins and their asymmetry. By examining the maps of the morphotectonic indexs of the region, it can be concluded that the thrust faults have had a significant impact on the morphology of the northwestern Sahneh.
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