پديد آورندگان :
آفريده ، فايزه نويسنده كارشناس ارشد ژيومورفولوژي، دانشكده جغرافيا، دانشگاه تهران , , اسدي ، اكرم نويسنده كارشناس ارشد ژيومورفولوژي، دانشكده علوم جغرافيايي، دانشگاه خوارزمي ,
چكيده لاتين :
Introduction
Tectonic geomorphology studies the role of tectonic processes in formation and evolution of landforms. So, in tectonic geomorphology it is studied forms, textures, and different landforms on earth surface that are affected by tectonic factors. To evaluate completely the tectonic activities, it is necessary to identify speed and distribution of geomorphologic processes and for this reason, it can be used different geomorphological methods and ways. Geomorphic indicators are valuable ways in order to analysis land forms and to evaluate tectonic activities in different regions. It is because by using these indicators, it is possible to recognize interchanges due to tectonic activities relatively fast or even slowly. The present paper with studying tectonic of Taleghan valley in Iran, has investigated its effect on quaternary landforms in studied area. To achieve this subjective, the level of tectonic activity of area has evaluated by calculating 7 indicators like: sinuses of stream index, gradient of river index, non-converge of stream index, proportion of direction to height of valley index, form of basin index, area of fan index and finally slope of fan. The studied area has located in north west of Iran. This area is in a synclinal which has expanded west- east between longitude of 50, 58 and latitude of 36, 11 until 36, 23. From the point of view of geology categories, the studied area is in southern mountains of central Alborz.
Methodology
Firstly, related literature review about the subjext of research has done by coherent documents along with photography, control and recognition of landforms of the area and studying the role of tectonic in their formation and evolution. In this research,, it has used some materials and instruments such as GPS to determine the location of land forms, Arc GIS software to draw needed maps and calculating the indexes, Photoshop for preparing images, topographical map with scale of 1:50000 of Fashand and Abyek and geological map of Shokran with the scale of 1:100000 as well. Finally by calculating seven indexes as noted earlier (S, SL, AF, VF, BS, AF, SF) the level of tectonic activity of study area has gained.
Results and Discussion
The concluded results show the existence of middle and average level of tectonic activity in studied area. Index of SL is an index that has been affected mostly in this area. In calculations, SL is about 255.07 that means this index did not have a similar amount to other indexes that it can be related to locating the river in the valley and lowering the slope of river and also topographic slope of whole area. The index of AF which show area of fan is 0.94, show that expanding the fan of the area is more affected by area of basins rather than tectonic. In the study of index of fan slope (SF) with the amount of 0.51 it is concluded that slope of fans is dependent on slope of basin. The reason for this is that the most of fans are in the left side of valley. This side of valley has been elevated because of tectonic activities and obviously its slope has increased. The index of AF which is 40.7 also show a tectonic disgorge in left side of basin specially in the final part where it seems there are some faults. Another index is S, the index of gradient of river which is 1.088 show an unbalance in the river and the reason is some faults in lower parts of the stream. Index of VF has estimated 0.57 show the existence of V form valleys. These types of valleys have been built by tectonic. The transformation of valley (being V form) is evident in lower part of the river until the valley gets narrower and this is exactly where fault of Taleghan has crossed from its west very closely to it and finally the area had heightening and unbalancing.
Conclusion
The field works done in the studied area has caused to identify and determine some witnesses of the impact of tectonic and geological activities on the area. The existence of different slopes in terraces, heightening and elevation difference around Taleghanriver, unbalance and disarrangement in morphological phenomenon around valley and narrowing the valley, all are showing and explaining the role and effect of tectonic on land forms of the studied area.
Generally, the existence of different slopes in terraces show the sediments are fouling corresponding to the present conditions. Sometimes, the sediments are happening in a calm environment, but the conditions and circumstance that emerge after the fouling can cause a transition in stratification. One of these transitions is different slope among sediments. Heightening and elevation difference around terraces of Taleghan valley, the quaternary in the studied area has formed form five eluvium terraces. Among them, three eluvium terraces has recognized and determined and it is obvious and evident the impacts of tectonic on them.
Heightening and unbalancing in rugged and mountains around the river, the existence of substational faults and even secondary faults in the area spacially in lower part pf basin and close to Taleghan dam, has remained small and large footprints and witnesses. One of the most important of these footprints is the existence of disgorging and faulting along with main fault of Taleghan inside the rugged mountains of this area.
Narrowing the area, one of the other tectonic impacts has seen is narrowing special part of Taleghan valley. This phenomenon has passed from the west of region where the main fault of Teleghan is crossed. A pressure movement has caused to narrow the valley in this part. The level of tectonic activity of the studied area using different indexes and indicators has estimated. But it is important to note that the calculated amount for each index is dependent to morphology of the valley. As the general calculation for whole indexes, the level of tectonic activity for the studied valley has evaluated almost medium or middle level. But gaing the level that has claculted from the average measure estimated from indexes, is dependent highly on morphology of valley.
