تحليل كمي تاثير ليتولوژي و تكتونيك بر نيمرخ طولي رودخانه مطالعه موردي: رودخانه اوجان چاي

Quantitative analysis of lithology and tectonics effect on river longitudinal profiles Case Study: Ujan Chai River

نيمرخ طولي رودخانه يافته‌هاي با ارزشي را در مورد تحول و تغييرات محيط‌هاي رودخانه‌اي در طول زمان در پي داشته است. در مقاله حاضر به بررسي تاثير ليتولوژي و تكتونيك بر روي نيمرخ طولي رودخانه اوجان‌چاي پرداخته‌شده است. اين رودخانه به طولkm35/77و جز سيستم زهكشي آجي چاي مي‌باشد.اطلاعات‌پايه جهت انجام كار،نقشه 1:100000 زمين‌شناسي شهرستان بستان‌آباد، نقشه هاي توپوگرافي حوضه و نرم‌افزارArc GIS9.3مي‌باشد. براي ارزيابي حوضه به لحاظ تكتونيكي از شاخص هاي تكتونيكي SL , V, Af, IC و منحني بي بعد(H/HO –L/L0) استفاده‌شده است. در اين مطالعه حوضه اوجان‌چاي به ده زير حوضه تقسيم شد. براي تمامي زير حوضه‌ها شاخص‌هاي تكتونيكي موردمحاسبه قرار گرفت.در بخش دوم كار با استفاده از ترسيم نيمرخ طولي زير حوضه‌ها و انطباق سازند‌هاي زمين‌شناسي و گسل‌هاي موجود به بررسي تاثير عوامل موثر بر عدم يكنواختي و ناپايداري نيمرخ رودخانه پرداخته شد. داده‌هاي شاخص‌هاي تكتونيك به همراه نقشه شيب تهيه‌شده براي حوضه بدين‌صورت ارزيابي شد، كه فعاليت زير حوضه‌هاي 1،2،3 به دليل قرا گيري در دامنه كوهستان سهند بيشتر متاثر از شيب مي‌باشد. فعاليت زير حوضه‌هاي 6 و 7 مربوط به گسل تبريز مي‌باشد. بنابراين همبستگي برقرارشده بين شيب حوضه و شاخص‌هاي V و AF به ترتيب مقدار 4/0 و 39/0 به دست آمد.در ارتباط با تاثير عوامل ليتولوژي و تكتونيك بر نيمرخ طولي در زير حوضه‌هاي 2،3،5،7 هر دو عامل ليتولوژي و تكتونيك موثر بودند. زير حوضه 6 به لحاظ تكتونيكي فعال‌ترين زير حوضه ارزيابي شد. در اين زير حوضه عامل برتر غيريكنواختي نيمرخ طولي عبور گسل تبريز از بخش مياني حوضه و گسل‌هاي فرعي ديگر مي‌باشد. درواقع ارتباط بين تكتونيك و ليتولوژي بر روي نيمرخ طولي به‌صورت اثر معكوس ارزيابي مي‌گردد.

Introduction Longitudinalprofile of the river bed is changing in response to variety of human and natural changes throughout the valley for that river to their Longtitual profile adaptation reduce these changes. (Schneider et al, 2003: 9). Any changes in the river system and disruption in its balance will followed by river response to adjustment. Balance in river system need balance state between transport and sedimentation Longtitual profile in one side and digging in other side. Relationship between geological structure and stones and their resistance plays an important role in water network channels justification (Mahmoudi, 129:1380). In this regard, river Longtitual profile extensively be used as an indicator to geomorphological evolution (Goodrich and Bishop, 2007; Duvall et al, 2004; Bishop, 2007). Fundamental studies of longitudinal profile of rivers has been seen in Hawke Research (1973). Another approach for using the river longitudinal profile of steep analysis is area that for river analysis and tectonic evaluation in local and regional scales (Weil Guvs, 1994). Khatibi (1384) with a change in any of the variables, such as changes in the River forces (Increase or decrease the flow) or resistance forces in the bed, longitudinal profile slopes will change. (Bayati Khatibi and Heydarzadeh Gan, 1384: 31).Allen Klav and Peter Comfort (1978) Lack of uniform longitudinal profiles were compared to changes caused by lithology. Results of previous studies indicate, River longitudinal profiles by lithology, renewed erosion processes caused by tectonics are affected by the level down. The purpose of this study is Quantitative analysis of lithology and tectonics effect on river longitudinal profiles Case Study, Ujan Chai River. Methodology The indexes that were used to evaluate the tectonic influence include IC (Index of Concavity), V, AF (Asymetric factor), and SL (Stream length-gradient index) and dimensionless curves H/HO-L/LO (ratio of altitude – ratio of distance), besides some 1/100000 Geological maps and 1:50000 topographic and Digital Terrain Model (DEM) with 30m resolution in ArcGis 9.3. Results and Discussion The data in tectonic indicators and steep map show that two parts of the basin have slopes more than 10 percent. One case is for up basins this is in slopes that have highest steeps another case related to basins 6 and 7. Whereas Tabriz fault passes through basin 6 and this fault several times has been worked we see upwelling around fault. This indicator relate to river length and elevation obtained. Erosion in these basins has relative excellence. V and SL indicators for sub-basins in major basin is for these activities support. In 8, 9 and 10 sub-basins V indicator show highest ratio Impact of lithology on longitudinal profiles: Lithology is considered as a major factor in the longitudinal profile. In the absence of faults, we also have seen a fracture in profile in different basins.Based on Adaptation and overlay geological maps and drawn longitudinal profiles we can introduce 2 kinds of fractures. - Fractures with lithology changes reflected on the longitudinal profile. - A fracture within a lithology is established that generally Tectonics is causing it. Factors associated with changes in river longitudinal profile have significant relationship between slope and contributing factors to the lack of uniformity. Basin where most material is granite and Granudyurit. Riverbed has resistance against the corrosive actions these parts is upper than that parts that have loose formation. Most of the land in the basin has been made from granite, volcanic ash, conglomerate and sandstone of the Terraces. Where faults activated disrupted the uniformity of the profile and where there is no fault existence of loose and hard formations together is main reason to uniformity disruption. Conclusions Tectonics and lithology role on longitudinal profiles of Ujan Chai River showed that basins 2,3,5,7 are controlled by both lithology and tectonics, but, existence of fault in basin 6 result in fractures within channels in different parts of longitudinal profile. Correlation between the slope of basin and AF and V indicators in order show 0.4, 0.39 values that is these values show that tectonic activities result in more slope steep and impact on channel longitudinal. If we attention to the changes in middle part of the basin both lithology and tectonics are present, but in the output of the main basin lithology effects is greater and there are no Tectonic effects.