Paleostress reconstruction of Paleozoic rocks in the Central Alborz, based on stress inversion method, Shahrestanak- Marzanabad Section

Alborz mountain range is formed by collision between Central Iran microplate and Eurasia plate in Late Triassic. Facieses studies on Alborz and Central Iran indicate a passive margin with epicontinental shelf deposits during Paleozoic Era. This study represents orientation of stress and paleostress analysis of the central Alborz, in Chalus section between Sharestanak and Marzan Abad, based on fault planes and slickenlines for all Periods of Paleozoic, but Silurian and Devonian. Since many tectonic events occur after the Paleozoic Era in the Alborz range so those faults are used, which formed during sedimentation and not reactivated by later events. Primary results indicate a proximately North-South extension in Cambrian, Ordovician, Carboniferous and Permian Periods. Since there is no any outcrop from the Silurian period in the study region and outcrops of the Devonian period are so scarce and were not separable, data acquisition was not done. Rotation of the Gondwana continent from Precambrian period to carboniferous period, Alborz and Central Iran as a part of the continent, as well as rotation of the Hercynian blocks from time of separation of the Gondwana continent and move toward the Eurasia continent until the collision of time are calculated for the analysis of stress field during its activity. So the preliminary results are restored by the same amount as the rotation that was done before along vertical axis. In such situation, investigates show that orientation of main tensile stress in the Permian, Carboniferous, Cambrian and Ordovician periods was northeast-southwest, east northeast-west southwest, west northwest-east southeast and northeastsouthwest, respectively.