Orientation of Cambrian-Devonian Extension Phase in the Eastern Alborz: Paleostress Analysis on the Growth Fault Data

The Alborz Mountain range is formed by collision between the Central Iran, in south, and Eurasia plates, in north, since Late Triassic. Facies studies of sedimentary rocks as well as geochemistry of volcanic rocks of Paleozoic formations on the Alborz and Central Iran indicate sedimentation in rift system and shelf and epicontinental shelf in passive margin of Gondwana. This study represents direction and paleostress analysis of the eastern part of Alborz based on geometry and kinematics of faults for the Cambrian, Ordovician and Devonian Periods. Since many tectonic events occur after the Paleozoic Era in the Alborz Mountain range so just growth faults, active during sedimentation, which were not reactivated by later events were used for paleostress analysis. In total 19 stations, including 297 fault data are measured north of Damghan-Shahrud area. The data were rotated to the first position based on fold axes, and FSA software (Fault Slip Analysis) was applied to calculate orientations of principal stress directions. All of the measurement stations show a proximal North-South extension in Cambrian-Devonian Periods.