Folding mechanism investigation of the Tarom Metallogenic Zone based on fracture patterns, NW Qazvin

Structurally, the Tarom Metallogenic Zone is located in an NW-SE trending anticline with 50 km wave-lenght, consists of the Karaj formation equivalent units and Neogene red beds. This anticline was created during the Alborz orogen formation- related phase has multiple fractures with NW-SE, NE-SW, and E-W trend. Detailed mesoscopic and microscopic investigations of the existing fractures for studying their propagations during folding, including their relative age, sequential deformation of the fractures in various beds, distribution of the fractures, and their changes during the following geological events, were performed many times. Comparison of various fracture patterns in folded layers not only illuminates the brittle deformation successions but also resulted in the detection of the main fold formation mechanism of the studied area. Based on the existing evidence at limbs of the anticline including 1- The existence of parasitic folds in soft layers, 2- Creation of layer- parallel shearing related strata-bound fractures in soft layers on various scales. Dyke intrusion into pre-existing fractures at fold limbs, preferentially has been happened in soft beds, especially in the Karaj formation equivalents pencil shales. While at the hinge zone, they have been created in hard layers, for example, andesite and basalt. The flexural slip mechanism is proposed for the Tarom Anticline.