تحليل تنش ديرينه در منطقه شيرشتر (يكي از شاخه‌هاي شمالي گسل نهبندان)

Paleostress analysis in the Shirshotor area (One of Northern Branches of Nehbandan fault

از ديدگاه زمين ساخت منطقه مورد مطالعه در زون زميندرز سيستان واقع شده است. هدف اين پژوهش بررسي تغييرات راستاي تنش بيشينه (σ1) در طول تاريخچه‌ي زمين ساخت منطقه با كمك نشانگرهاي ساختاري موجود در منطقه شيرشتر (جنوب شرق سربيشه) مي‌باشد كه از جمله اين نشانگرها مي‌توان به گسل‌ها، برگوارگي‌ها و رگه‌ها اشاره كرد. براي بررسي تغييرات تنش ديرين منطقه از روش‌هاي مختلف تحليل تنش ديرينه بر روي مشخصات هندسي حركتي گسل‌هاي منطقه به كمك نرم افزارهاي مربوطه استفاده شده است كه نتايج به دست آمده نشان مي‌دهد كه منطقه مورد پژوهش دو راستاي رژيم تنشي را در طول تاريخچه زمين ساختي بر اساس سن واحدهاي سنگي تجربه كرده است. راستاي اوليه تنش بيشينه به صورت شمال باختري – جنوب خاوري از زمان كرتاسه تا قبل از ائوسن بر منطقه حاكم بوده و راستاي تنش شمال خاوري – جنوب باختري از زمان ائوسن تا زمان كنوني حاكم بوده است كه با راستاي رژيم كنوني منطقه همخواني دارد. همچنين با تلفيق نتايج بدست آمده از تحليل تنش با نتايج بدست آمده از جنبش‌شناسي برگوارگي‌ها و رگه‌هاي منطقه مورد مطالعه، تغييرات راستاي تنش بيشينه (σ1) چرخش ساعتگرد را نشان مي‌دهد.

Recent geological studies represent that the lithosphere is evolved by time and place. Hence, one of the essential ways for interpreting how structures and deformation are formed, it appeared in finding paleostress direction. Reconstruction of paleostress is performed by using analysis of tectonic data with conjugate fault (Anderson, 1951), moving surfaces of faults (Arthaud, 1969), two-sided perpendicular to each other (Carey and Brunnier, 1974; Angelier and Mechler, 1977; Angelir, 1990; Ramsey and Lisle, 2000) and inversion method (Yamaji, 2000). Analysis of the paleostress phases performed by the inversion method measured with using fault plane in southern Birjand city. Results indicate at least two stress phases have been operating in the study area. After changing the direction of phases trends; extension and deformation are observed and on the structural component (Moussavi et al., 2011). The study area is located in the Sistan suture zone. This paper aims to investigate the variation of maximum stress axis (σ1) along with the history of the tectonic regime with the use of structural markers, including faults, foliated structure, and veins. In order to investigate paleostress variations, have been used stress analysis methods on fault data with using the relevant software. The results indicate two stress trends during tectonic history based on the age of rock units. The initial direction of the maximum stress axis is acted NW – SE since Cretaceous to the before Eocene, after that the direction of stress has been changing toward NE- SW since Eocene to the present time. Furthermore, by combining between the results obtained from stress analysis with the results obtained from the kinematic of veins and foliation indicate the variations of directional stress field represent a clockwise rotation. 2-Methodology In order to recognize the arrangement of the paleostress axis establish a relationship between main structures and direction of stress axis during the tectonic history, and based on the litho-stratography unit 2-1- Slickenlines analysis Analysis of fault slickenline is the most reliable way to access the distribution of paleostress. Indeed, in term of structural form based on the same tectonic stress regime. Finding them in proportion to the age and type of rocks units forming the area seems logical and will result in the least error. In order to access this purpose is used, the slickenline data of fault plane