Geometric pattern of the North Tehran structural zone, Alborz Mountains: A Review

In the study area, a comprehensive review on the structural geometric model of the Mosha-North Tehran fault system, presented by previous workers, has been done. This area is located in the Alborz Mountain range with a length of about ۲۰۰۰ km and an approximate width of ۱۰۰ km is located on the southern shore of the Caspian Sea. This belt with the general E-W trend is a part of the great Alpine-Himalayan belt. Our study area includes a structural lozenge with an overall WNW-ESE trend. This structural zone is bounded by a fault system with a left-lateral or right-lateral strike slip mechanism and small contractional or extensional components during the geological time. These faults are Mosha fault zone (MF) to the NNE and North Tehran fault zone (NTF) to the SSW. NW-striking thrusts, the Purkan-Vardij Thrust (PVT) and the likewise striking Emamzadeh-Davud Fault (EDF) are also other remarkable features in the study area. The blocks enclosed between the two fault zones have undergone alternately uplift and subsidence at different time periods of Mesozoic and Cenozoic for several times. Therefore, in the distance between these faults, an interchangeable transtensional duplex/half-negative flower structure and transpressional duplex/half-positive flower structure has been formed. In other words, inversion tectonics has been conducted and so, extensional and contractional regime has interchanges alternately to each other. This area is named Tehran transtensional /transpressional duplex structure. During Oligo-Miocene, due to the northwestward movement of the South Caspian Basin with respect to the Eurasia, an inversion phenomenon occurred at this time, and a transtensional (right-lateral with extensional component) environment turn into a transpressional (left-lateral with small contractional component) one. Moreover, the distances between Kandovan and Taleghan faults and also between Taleghan and Mosha faults are called Taleghan pop-down and Taleghan pop-up structures, respectively. Finally, we provided a ۳D block diagram comprising all structures in the study area. Totally, we can say that the fundamental purpose of this study is providing a new geometric pattern for the Mosha-North Tehran fault system.

کلیدواژه ها:

Central Alborz ، Geometric pattern ، mosha fault ، North Tehran fault ، half flower structure