Determining paleo-stress based on the study of discontinuities and folds in Zagros Collision Zone; Case Study: Kermanshah Region

The studied zone is in the Northern part of  Zagros Suture Zone (Kermanshah). The presence of deep sea sediments, oceanic crust remnants, platform carbonates, igneous and metamorphosed rocks of active margin and carbonate sequence of passive margin that are assembled in the studied area show a compressional tectonic regime from the late Cretaceous up to the present. As a result of convergent regime, a very complicated structural zone is developed. The main purpose of this study is stress characteristic analysis in Zagros Suture Zone (Kermanshah).To recognize and study the arrangement of stress axes a great amount of data were gathered from the folds axial surface and the faults which are appeared within the rocks specially the radiolaritic rocks. The data includes characteristics of fault surface geometry, fault slip and lineation slip. The stress recording patterns for data in this study is Multiple Inverse Method and comparison with stress position by using folds axial surface.  By studying folds it was obtained the situation of main stress σ1, σ2 and σ3 respectively as 029, 127, 234 and by using the method Multiple Inverse Method, the situation of main stress is obtained as 059, 304, 194. Based on the investigations in the study area and measurements on Cretaceous rocks, the results show that the main stress direction since Cretaceous up to the present is northeastern with minor changes. The estimations of stress direction were the same in both folds and faults. As a result, the shortening direction has been constant, so the shortening faults all show one direction of stress.