Determination of stress state and tectonic regime changes in the brittle structures of Chah Yusuf Mountain (East of Gonabad)

In this study، structural elements، such as faults and fractures and their formation mechanisms and relationships with tectonic regime of Chah Yusuf Mountain in East of Gonabad city have been recognized and discussed. Their relation with regional fractures، based on data’s from satellite image process and field data، is also shown. Major faults in this area were identified by using fault plain features such as striations، stretching vein and cumulative steps of minerals that helped us to determine fault mechanisms. In general، faults were oriented in three main directions: 1) Reversed faulting along N90-120˚، 2) Right lateral strike –slip faults along N140-160˚ and 3) Normal faults along N0-15˚. Based on the obtained data and using the inversion method، the orientation of the principal stress axes (σ1، σ2 and σ3) and the ratio of the principal stress differences R in the studied area were analyzed. The results showed two different tectonic regimes in the formation of regional structures: 1) Compressive tectonic regime، major stress along NNE-SSW، which generated structures of folds and reversed faults. 2) Shear tectonic regime، compressive stress along NE_SW and tensile stress line NW-SE، which generated structures such as strike-slip faults، normal faults، vein and tensile fracture. So، the major stress direction in this region is NNE-SSW، which shows its relation to the Late Cenozoic Arabia –Eurasia oblique continental collision.