آناليز خطواره هاي گرانيت كوه سفيد و سنگ‌هاي اطراف، شاهدي بر فعاليت گسل‌هاي پهنه زمين‌درز سيستان، جنوب شرق ايران

Lineaments analysis of Kuh-Sefid granite and surrounding rocks, evidence of tectonic activity of Sistan Suture Zone faults, southeastern Iran

گرانيت كوه سفيد در پهنه زمين‌درز سيستان، و قسمت مركزي نوار گرانيتوئيدي زاهدان-سراوان قرار دارد. شكستگي هاي متفاوتي اين گرانيت، هاله دگرگوني و سنگهاي اطراف را تحت تاثير قرار داده اند. در اين مطالعه با بررسي اين ساختارها به نقش گسل‌هاي اصلي و جايگيري توده گرانيتي در توسعه شكستگي‌ها پرداخته شده است. در ابتدا با استفاده از پردازش تصاوير ماهواره‌اي و مطالعات دورسنجي، سيستم شكستگي‌ها و گسل‌هاي موجود در توده‌ نفوذي و سنگ‌هاي ميزبان استخراج گرديد. سپس جهت تنش حد اكثر در منطقه و روابط قطع شدگي از يكديگر متمايز و دسته بندي شدند. با توجه به اطلاعات به دست آمده دو فاز دگرشكلي از قديم به جديد پيشنهاد مي‌گردد . فاز پيش‌رونده D1 كه با جهت تنش حداكثر شمال شرق- جنوب شرق باعث توسعه خطواره‌هاي مزدوج شمال شرق-جنوب غرب شده و در ادامه با فعاليت گسلهاي به موازات گسل سراوان محيط مناسب جهت نفوذ توده گرانيتي فراهم شده است. همزمان با نفوذ توده شكستگي‌هاي شعاعي در سنگهاي اطراف توسعه پيداكرده‌اند. بعد از سرد شدن و ايجاد هاله دگرگوني، تداوم تنش با همين امتداد باعث ايجاد شكستگي‌هاي مزدوج در توده اصلي شده است در ادامه فاز D2 ناشي از تكتونيك فعال منطقه با ايجاد گسل‌هاي شمالي- جنوبي تمامي ساختارهاي قديمي را قطع و جابجا مي‌كند.

Two mechanisms such as horizontal and vertical principal stress can create different fractures and faults in the rocks. The first one is tectonic forces as a result of the motion of plate tectonics and the second one is buoyancy forces as a result of magmatic activity (Ruch et al., 2016). The Kuh-Sefid granite emplaced in the flysch rocks of eastern Iran, southeast of Taftan, and the central part of the Zahedan-Saravan granite belt has provided a good opportunity to study the influence of tectonics and magmatic activity in creating fractures in this region. This granite, metamorphic halo, and surrounding rocks have been affected by different fractures system. The main purpose of this article is to investigate the role of tectonics and the main faults in the emplacement of Kuh-Sefid granite and the creation of obvious lineaments in this mass and the surrounding rocks, which can be a suitable basis for further studies on this little-known area. Materials and methods In order to analysis of fractures and faults in the study area at the first, the system of fractures and faults in the intrusive mass and host rocks are extracted using remote sensing and satellite image processing. In this study, Landsat 8 satellite images with pass number LC08_L1TP_156041 were used to identify the lineaments. Then, using GIS, these structures were differentiated and categorized based on the orientation, regional maximum stress, and their cross-cutting relationship. Results and discussion The granite unite has several main north-south lineaments parallel to each other. In metamorphic units, based on the position of this unit in relation to the granite unit, these structures were divided into five equal parts that have different orientations. Lineaments analysis of sedimentary rocks (Flysch): Based on the position of this unit in relation to the granite unit, extracted lineaments were divided into nine equal parts and then the rose diagram of each part was drawn. According to the genetic relationship between fracture structures and the direction of maximum stress in the region (Angelier, 1989; 1991), long lineaments that have displacement along their length were considered faults and used to estimate the direction of the maximum principal stress in the region. Kuh-Sefid granite as the youngest geological unit in the region, the granite mass intruded into the sedimentary rocks and creates a metamorphic halo in them. The existence of systematic fractures of the main mass shows that it was affected by tectonic stresses after cooling, but it should also be noted that the rise of granite masses can cause vertical stress and related fractures in the host rocks. These features have provided a suitable situation to investigate the tectonic history of the region and the effect of the main faults and the rise of the granite mass on creating brittle structures such as fractures and faults. The data obtained from remote sensing studies and statistical analyses of lineaments and faults at a glance show relatively active tectonics affected by different phases in the region According to the obtained, data two-phase of deformation from old to new are suggested. D1: progressive phase, which with the direction of maximum northeast-southeast stress causes the development of northeast-southwest conjugate fractures, and then the activity of faults parallel to Saravan fault provided a suitable environment for the intrusion of granitic mass. Simultaneously with the intrusion of the mass, radial fractures have developed in the surrounding rocks. After cooling and creating a metamorphic halo, the continuation of stress along the same direction has caused conjugate fractures in the main granite mass. Subsequently, the newer phase D2 due to the active tectonics of the region, by creating north-south faults, cuts and displaces all the old structures and Saravan fault. Conclusion: The extraction of lineaments of the Koh-Sefid granite, the metamorphic halo, and the surrounding flysch rocks show the role of tectonics and magmatic activity in creating of these structures. The study of cross-cutting relationships and the classification of faults and lineaments show two deformation phases in the region. The initial phase, which is proportional to the general stress along the northeast-southwest direction, is a progressive phase, and the final phase, in accommodates the active tectonic regime of the region, acting as north-south dextral strike-slip faults.