تحليل ساختاري و تكتونيك برگشتي نواحي فراديواره گسل شمال تهران

Reverse Tectonic and Structural Analysis of North Tehran Fault hanging Wall Area

منطقه مورد بررسي مجموعه‌اي از ساختارهاي زمين‌ساختي، به‌ويژه شكستگي‌هاي گوناگون و گسل‌ها و انواع چين‌خوردگي، را در خود جاي داده است. ساختار‌ها با سازوكار خاص متأثر از تنش‌ها (فشارشي‌ـ كششي) بوده‌اند. بر اساس شواهد زمين‌شناسي موجود در همه واحدهاي سنگي سازند كرج و نهشته‌هاي آبرفتي كواترنري در پهنه گسلي شمال تهران، اعم از خش‌لغزها و ساختارهاي C –S، سازوكار گسل شمال تهران تا قبل از پليوسن به صورت مورب‌لغز راست‌گرد با مؤلفه عادي و پس از نئوژن به صورت مورب‌لغز مي باشد كه در برخي مناطق مؤلفه معكوس غالب است و در برخي مناطق مؤلفه راستالغز چپ‌گرد غالب مي باشد . تحولات زمين‌ساختي گستره مورد مطالعه با يك مدل قابل ارائه است. بر اساس اين مدل، گستره بين دو گسل شمال تهران و مشاء به صورت يك ابر دوپشته در حال چرخش راست‌گرد (ساعت‌گرد) است. موقعيت تنش اصلي σ1 (عمود بر محور چين خوردگي يا راستاي كوتاه شدگي) در زمان تشكيل ساختارهاي شكل پذير منطقه راستاي شمال باختر- جنوب خاور داشته است.

Introduction: The study area has various types of geological structures, especially various types of fractures and folds. Evidence indicates that Structures with specific mechanisms in this area have been affected by Compressional - Tensile tensions. Materials and methods: To determine the direction of stress in the fault zone north of Tehran, from various tectonic evidences including fault slip scratches, Conjugated faults and folds in the Eocene rock units of Karaj Formation and Quaternary alluvium was used. For this purpose measured structures Was analyzed using Tectonic FP software and Angelier software was used for paleostress analysis of the area. Results and discussion: According to geologic observations in Karaj formation units and Pleistocene-Holocene deposits of North Tehran fault zone including Slickenside and S-C fabrics, before Pliocene the fault mechanism was right-lateral strike-slip and after that it has changed to oblique-slip some parts the revers component and in some other parts left-lateral strike-slip component dominates. The tectonic developments of the study area can be presented with a model. According to this model, the area between the two faults north Tehran and Mosha as a triangular block(Mega Duplex) is Turning right, This model is presented in accordance with the tectonic evidence presented below: The tectonic history of central Alborz in the study area is clearly evident and evidence of its compression N-S, NW-SE,NE-SW Has been left out, Seismic data recorded at the Institute of Geophysics of the University of Tehran shows the most seismic activity on the North Tehran Fault slope and its associated with the Mosha fault, By comparing the zoning of the area in terms of aggregation of tectonic structures and seismic data observed at the center of the study area, There is an elliptical basin that shows low tectonic activity. Given that the area is not Lithology significant, This phenomenon can be justified by the rotational model, So that the maximum stress and friction force is applied to the sides of this triangular block and the least to the center of the range, As a result, tectonic activity is minimized in the said area in the center. Axial surface of all folds harvested in Eocene rock units of Karaj Formation In the fault zone north of Tehran in sabu, Darkeh, Hesarak and Kan regions, they have an approximate northeast-southwest. Due to the geometric position of their axial surfaces for the stress of the region in the past, It was northwest-southeast. In the fault zone north of Tehran before Neogene in most areas of northwestern-southeastern stress an‎d the mechanism of faults was straight-slip rectilinear and the time of stress direction change was Neogene. In the Can region, based on the geometric location of the scratches, the landslides were investigated an‎d stretched folds in alluvial sediments of type C, which is the newest sedimentary unit in the region,The direction of tension in the region is northwest-southeast. Therefore, it can be said that in this area, after the Pliocene, the tension has not changed, unlike other parts of the fault zone north of Tehran. an‎d the recent Northeast-Southwest tension has not affected it. This part of the fault is likely to be affected by a smaller local stress.Due to the adaptation of the trend and mechanism of faults harvested in the region with fractures (Riddle) Also, the existence of conjugate faults, the mechanism of strike-slip fault north of Tehran is confirmed. East-west pressure force must Folds with a north-south trend in the region have been created by examining the region, No wrinkles are seen with this trend. This feature can be due to the block rotation in the studied sheet,Between the two driving faults north of Tehran and Mosha with straight-slip components an‎d has formed folds with a northwest-southeast trend.