Investigation of structural pattern and introduction of detachment surface of Alborz Mountain Range in the north of Damghan

The studied area is a part of Eastern central Alborz, bestween southeastern piedmont of Alborz (NW of Damghan) and North Alborz Fault (South of Sari). The Alborz Mountain range which forms the heights of northern territory, separated the Caspian Depression from Iran central plateau. The Alborz is one of the Iranian mountain ranges that were deformed during two Cimmerian and Alpine organic events. This deformation is continued until the present day. This research is based on the satellite images, field investigations, drawing structural sections, stratigraphic sequences from the folded and thrusted parts of Alborz Mountains. The studied area is composed of numerous anticlines and synclines from South to North as Tuyeh- Darvar anticline, Sabour anticline, Talma- Darreh anticline, Alikhani syncline, Tarkan anticline, Babr cheshmeh syncline and anticline. Some of these folds are related to faulting which occured due to the typical continuous shortening and faulting of Alborz crust and destroyed their original patterns. The function of main faults and specially thrust faults played an essential role on the present models of mentioned folds. Regarding the axes of the folds, the effective compression over the area has a North, North Waste-South, South-East direction. This direction is perpendicular to axial trend of folds.
The physico-mechanical properties of Alborz geological units caused development of detachment surfaces on main faults. The shortening intensity and large displacements have led to disappearance of a limb or whole  fold. In this study the three surfaces of detachment were introduced inside the stratigraphic sequences from Precambrian to middle Eocene based on the well-known and documented data.