Investigation on Geological Structures of Alvand Region (Southeast of Zanjan City) in Iran

Abstract

Investigating geological structures plays a major role in economy of engineering projects such as petroleum and mining industries. Therefore, it is pivotal to study geological features. The study area is located in northwest of Qazvin Province and Tarom mountains. Tarom Mountains are located in Western Alborz as referred to in Iranian geological units which has a northwest-southeast trend and is located on the Upper Cretaceous-Cenozoic Magmatic belt. This volcanic-plutonic belt has a northwest to southeast trend. The volcanic and intrusive units of the region that belong to Karaj Formation is composed of two members called Amand and KordKand that are affected by alpine orogeny movements. Different folds were geometrically analyzed in the region and based on the mapping of the data on the Schmidt network and the flute (1964) and Rickard (1971) charts; they were categorized as gently to moderate plunging and steeply inclined folds. Based on Twiss’s classification of folds (1988), findings showed most folds are sub-angular and in terms of the appearance ratio are in broad type. Using Ramsay’s (1967) classification and the pattern variation of the contour lines for some folds, they are all in category 1 and mostly in category 1B which can be considered as a flexural-slip mechanism. The results demonstrated that the process of all the axial surfaces and the axis of folds are generally in the direction of northwest-southeast. The faults taken from the study area are mostly reverse and strike-slip in the direction of northwest-southeast in accordance with the western Alborz.