پديد آورندگان :
مومني طارمسري، محمد نويسنده دانشجوي كارشناسي ارشد تكتونيك، دانشگاه خوارزمي , , ده‌بزرگي، مريم نويسنده استاديار دانشكده علوم زمين، دانشگاه خوارزمي , , يساقي، علي نويسنده دانشيار دانشكده علوم پايه، دانشگاه تربيت مدرس تهران , , نوزعيم ، رضا نويسنده استاديار دانشكده علوم پايه، دانشگاه بين‌المللي امام خميني قزوين ,
كليدواژه :
ايران مركزي , ازبك‌كوه , تكتونيك فعال , شاخص‌هاي مورفومتري , گسل كلمرد
چكيده فارسي :
منطقه ازبك‌كوه در ايران‌مركزي در پهنه گسلي كلمرد قرار دارد. گسل كلمرد يكي از گسل‌هاي مهم بنيادي ايران مركزي به شمار مي‌رود كه در كواترنري نيز فعال مي‌باشد. كوه‌هاي ازبك‌كوه در قسمت‌هاي شرقي تحت تاثير پهنه گسلي كلمرد قرارگرفته‌اند. همان‌طور كه ذكر شد گسل كلمرد در شرق ايران به‌عنوان يك گسل كواترنري در نظر گرفته مي‌شود و آخرين حركات اين گسل را به عهد حاضر نسبت داده‌اند، بنابراين برآورد شاخص‌هاي مورفومتري به‌منظور شناسايي تاثير تكتونيك فعال آن بر تكامل تكتونيكي حوضه‌هاي زهكشي ضروري به نظر مي‌رسد. لذا در اين مطالعه به تجزيه‌وتحليل 6 شاخص مورفوتكتونيكي مهم نظير گراديان طولي رودخانه، عدم تقارن حوضه زهكشي، انتگرال هيپسومتريك، شكل حوضه زهكشي، نسبت عرض كف به ارتفاع دره و پيشاني كوهستان پرداخته‌شده است. براي تشكيل حوضه‌ها بر روي منطقه موردمطالعه از نرم‌افزار Arc Hydro (از افزونه‌هاي نرم‌افزار Arc GIS) بر پايه داده‌هاي حاصل از مدل رقومي ارتفاعي استفاده‌شده است، سپس 6 شاخص مورفوتكتونيكي بر روي هر يك از حوضه‌ها موردمحاسبه و رده‌بندي قرارگرفته است. در‌نهايت، شاخص تكتونيك فعال(Iat) محاسبه گرديده كه بر اساس آن ازبك‌كوه به 4 رده فعاليت تكتونيكي بسيار بالا، بالا، متوسط و پايين رده‌بندي گرديده است. بر اساس شاخص IAT كمتر از 5 درصد از محدوده موردمطالعه، فعاليت تكتونيكي بسيار بالا نشان مي‌دهند، 27 درصد از منطقه موردمطالعه فعاليت تكتونيكي بالا، 50 درصد فعاليت تكتونيكي متوسط و حدود 20 درصد هم فعاليت تكتونيكي پايين را نشان مي‌دهند. در گستره مطالعاتي بيشترين سطح فعاليت تكتونيكي در بخش شرقي ازبك‌كوه مرتبط با فعاليت گسل كلمرد در نظر گرفته‌شده است. در بخش غربي نيز سطح فعاليت تكتونيكي بالا تا متوسط بوده كه نشانگر عملكرد پهنه گسلي غرب ازبك‌كوه مي‌باشد.
چكيده لاتين :
The Ozbak-Kuh mountain is located in the Kalmard fault zone in the Central Iran. Kalmard fault is considered as one of the fundamental faults of the Central Iran which is active in quaternary. Ozbak kuh mountain has been affected by Kalmard fault zone in the eastern part. The Kalmard fault has been known as a quaternary fault in the eastern part of Iran and it’s recently of movement is considered early. The values of geomorphic indices as well as Iat often change corresponding to the distribution of this fault zone. Therefore, estimation of the morphometric parameters to identify the effect of its recent activity on the tectonic evolution of the drainage basins of the study area is essential. In order to assess the relative tectonic activity through the Ozbak kuh area, subbasins and stream network were extracted by using Arc Hydro Tools software (an extension of Arc GIS software, ESRI) based on the DEM and in turn, 87 subbasins have been resulted. In this study, Considering the diversity of the morphotectonic features, six morphometric indices relevant to the river channel, drainage basin, and mountain fronts were computed for every catchment, and consequently, a single index (Iat) was calculated from the these indices for each of 87 subbasins to define the degree of active tectonics. The values for each basin were classified into 3 classes and the result of the classification for each subbasin is shown in maps and Tables. Thus, this study is addressed to analyze of six important Morphotectonic indices such as stream length gradient (SL), drainage basin asymmetry (Af), hypsometric integral(Hi), drainage basin shape (Bs), ratio of valley floor width to valley height (Vf), and mountain-front Sinuosity (J). Finally, the Index of the Active Tectonic (Iat) was calculated through which the Ozbak Kuh is classified into four tectonic activity classes, from very high to low; 1—very high (1.0?Iatb1.5); 2—high (1.5?Iatb2.0); 3—moderate (2.0?Iatb2.5); and 4—low (2.5?Iat) (El Hamdouni et al., 2007). The distribution of the four classes of Iat is presented in a well classified map. The indices represent a quantitative approach to differential geomorphic analysis related to erosion and depositional processes which include the river channel and valley morphology as well as tectonically derived features, such as fault scarps. We also evaluated the outputs of the morphometric analyses based on field-based geomorphological observations. Thus, these results are proved to be extremely beneficial to evaluate relative rates of active tectonics of this region. The Iat index classes computed within the study area, about 3% (7 Km2) is class 1 (very high relative tectonic activity); 27% (71 Km2) is class 2 (High Relative Tectonic Activity); 50% (131 Km2) shows moderate values of tectonic activity (class 3) and 20% (52 Km2) has the lowest values of relative tectonic activity (class 4) in the study area. In the study area, the highest level of tectonic activity in the eastern Ozbak kuh is assigned to activity of the Kalmard fault. Besides, in the western part, the tectonic activity level is high to moderate indicating the activity of the west Ozbak kuh fault zone. However, the central segment of the Ozbak kuh mountain represents low values of tectonic activity. Based on the geological map, the late Quaternary deposits are divided into two surfaces in the study area (Qt1- Qt2). The Qt1 surface (older gravel fans and terraces) is the latest stage of deposition in the late Pleistocene and Qt2 is the younger gravel fans and terraces in the lower level than Qt1(Ruttner et al., 1970). The geomorphological and geological evaluations, performed in the study area indicate that the Qt2 surface is the Holocene deposit (Ruttner et al., 1970), affected by the NNE-SSW trending faults in the west and east of Ozbak kuh mountain, and the Qt1 surface is the older alluvial deposit in the partial of Ozbak kuh mountain in the southwest of study area corresponding to the moderate tectonic activity. Aforementioned evidence corresponds well with the distribution of relative tectonic activity. Partially in the center segment of the study area almost with no significant fault indicates the low class of the tectonic activity. Iat is mostly high and partially moderate almost throughout the east and west part of the study area in the Ozbak kuh mountain which corresponds to a straight mountain front, asymmetric drainage basins, gorges, triangular facets and tilted or faulted alluvial deposits along the Kalmard and West Ozbak kuh fault zones. Nevertheless, the lowest Iat values (class 4) mainly occur in the central segment of the study area where all geomorphic indices suggest low tectonic activity.
