پديد آورندگان :
بابائي، شيما دانشگاه خوارزمي، تهران , ده بزرگي، مريم دانشگاه خوارزمي - دانشكده علوم زمين، تهران , حكيمي آسيابر، سعيد دانشگاه آزاد واحد لاهيجان - دانشكده علوم پايه , حسيني اصل، امين دانشگاه شهيد بهشتي - دانشكده علوم زمين
كليدواژه :
البرز مركزي , حوضه زهكشي , شاخص ژئومورفولوژي , زمين‌ساخت فعال
چكيده فارسي :
يكي از روش‌هاي بررسي حركات زمين‌ساخت فعال، استفاده از اطلاعات ريخت‌زمين‌ساخت است. اندازه‌گيري كمي شاخص‌هاي ژئومورفولوژي، يك ابزار مهم براي تعيين سطح فعاليت زمين‌ساخت منطقه است. اين اندازه‌گيري‌هاي كمي امكان مقايسه زمين‌ريخت‌هاي مختلف و محاسبه متغيرها را فراهم و شناسايي نرخ فعاليت زمين‌ساختي يك منطقه را امكان‌پذير مي‌سازد. در اين مطالعه، زمين‌ساخت فعال البرز مركزي در حوضه‌هاي هراز و نور- نوشهر با اندازه‌گيري شش شاخص ژئومورفولوژي ناهنجاري سلسله مراتبي (∆a)، انشعابات (R)، انتگرال و منحني فرازسنجي (Hi)، برجستگي نسبي (Bh)، تراكم زهكشي (Dd) و ضريب شكل (Ff) مورد ارزيابي قرار گرفت. ابتدا با استفاده از مدل رقومي‌ارتفاعي (DEM) 30 متر در محيط GIS حوضه‌ها و آبراهه‌هاي منطقه مورد مطالعه استخراج شد، سپس شاخص‌هاي ژئومورفولوژي در هر زيرحوضه اندازه‌گيري شد. هر شاخص به سه رده به لحاظ فعاليت زمين‌ساختي تقسيم شد و در نهايت براساس تقسيم‌بندي هر شاخص، سطح فعاليت زمين‌ساختي كل برمبناي شاخص زمين‌ساخت فعال نسبي (Iat) منطقه تعيين شد و گستره مورد بررسي به 4 رده فعاليت زمين‌ساختي بسيار بالا، بالا، متوسط و كم تقسيم شد، سپس نقشه پهنه‌بندي سطح فعاليت زمين‌ساختي درگستره مورد مطالعه ترسيم شد. نتايج حاصل از شاخص زمين‌ساخت فعال نسبي نشان مي‌دهد كه گستره مورد بررسي داراي فعاليت زمين‌ساختي بسيار بالا و بالا است به‌ويژه در مناطق منطبق با گسل‌هاي شمال البرز، خزر، گلندرودشمالي و جنوبي، بلده و گسل‌هاي جنوب باختري و چين‌خوردگي‌هاي جنوب خاوري محدوده مورد بررسي را تاييد مي‌كند، همچنين شواهد زمين‌ريختي حاصل از مشاهدات صحرايي اثبات كننده نتايج حاصل از شش شاخص ژئومورفولوژي در گستره مورد مطالعه است.
چكيده لاتين :
One of the methods for study the movements of active tectonics is utilizing the information about morphotectonic data. The quantitative measurement of morphometric indices is an important tool for determining the level tectonic activity of the area. These quantitative measurements provide the possibility of an objective comparison between different kinds of morphologic features and calculation of unintelligible variables, as well as the ability to identify the rate of activities of an area’s tectonics. Morphometric analysis of a basin provides information about hydrological conditions, nature of rock formation and geologic structure of the basin. Faults and folds can cause to deform landforms and documentation of any departure from their unperturbed shape can serve to define the magnitude of deformation. Consequently, the recognition and measurement of such displaced or deformed markers is critical to many morphotectonic studies. In this study, active tectonics of the Central Alborz in Haraz and Noor- Noshahr basins with measuring morphometric indices has been surveyed. The study area is located in the Central Alborz and khazar, North Alborz, Baladeh and North and South Galandrud faults are some of the most important faults of this area. There are many folds in the southwestern and a lot of inferred faults in the northwestern of study area. General trend of study area is NW- SE. according to the situation of the area tectonic and the position of different rivers, surveying the morphometric indices is very useful to determine the rate of active tectonics of area. So it’s tried to determine the level of active tectonics of area by using the morphometric indices. In this study, in order to assess tectonic activities new morphometric indices were used. To assess tectonic activities in the area, six morphometric indices of the Hierarchical anomaly (∆a), Bifurcation (R), Hypsometric integral and curve (Hi), Relative relief (Bh), Drainage density (Dd) and Form factor (Ff) have been assessed. These indices can show the effects of active tectonics on the area and the effects of geology structures on the drainage system. The changes of active tectonicon drainage system can be shown by these six indicies. The Bifurcation index depends on the presence of hierarchical anomalies in the network and Hierarchical anomaly and Bifurcation indices are highly sensitive to the effects of the active tectonics. The Hypsometric integral describes the relative distribution of elevation in a given area of a landscape particularly a drainage basin. The high rate of Relative relief index represents the high level of uplifting that is because of active tectonics of area. Drainage density index in basins that have active tectonics is lower. Basins are longer in active tectonics of area. First, sub basins and streams were extracted by using digital elevation map (DEM) with a horizontal resolution of 30 m in geographic information systems (GIS) and using hydrological functions of GIS (Arc Hydro) and then after some reformations, 27 sub basins were formed. In next step, the geology units and structures were extracted from geology maps 1: 100,000 in study area. Then, each of the indices is measured in every 27 extracted sub basins. In order to better survey in this study, each index was divided to 3 classes in terms of active tectonic and indices of the Hierarchical anomaly (∆a), Bifurcation (R), Hypsometric integral and curve (Hi), Relative relief (Bh), Drainage density (Dd) and Form factor (Ff) were classified according to the their values and eventually according to division of each index, the level of active tectonics based on relative active tectonics index (Iat) was determined. Based on Iat values, the study area was divided into four classes: Class 1 (very high relative tectonic activity), Class 2 (high), Class 3 (moderate) and Class 4 (low). The distribution of the four classes was mapped in the study area. The results of measuring of six morphometric indices and assimilating them in to field observation indicate intense neotectonic activities in the studied area. The result of Iat index indicated that study area has high and very high active tectonics especially in the areas matched with khazar, North Alborz, Baladeh and North and South Galandrud faults and folds in the southwestern and faults in the southeastern of study area and the Northwestern of the study area has moderate active tectonics. In addition the results are consistent with field observations on landforms and geology. The results of morphometric indices and filed observations indicate the activity of khazar, North Alborz, Baladeh and North and South Galandrud faults and folds in the southwestern and fault in the southeastern of study area and the Northwestern of the study area.
