Structural Analysis Of Shah Allah Ditta And Adjoining Areas Of Islamabad, Pakistan

Abstract

The study area is part of Margalla Hills and is the south-western extension of the Hazara Kashmir Syntaxis in northern Pakistan. The area is highly complex and intensely deformed. The detailed mapping has recognized six lithological units ranging in age from Jurassic to Miocene. The Jurassic sequence is represented by the Samana Suk Formation. The Cretaceous rocks Chichali, Lumshiwal, and Kawagarh are missing in the study area whereas the Paleocene rocks exposed are Hangu, Lockhart and Patala formations. The Eocene sequence is represented by Margalla Hill Limestone and Murree Formation of Miocene. Structural analysis is carried out with the help of field mapping. Main Boundary Thrust (MBT) is well exposed in the study area which is part of the NW Himalayan Foreland Fold and Thrust Belt of northern Pakistan and is related to the main zone of Himalayan convergence. It is marked by the thrusted contact between the Samana Suk Formation and the Murree Formation. Two thrust faults are mapped along the MBT, the Margalla Fault and the Kot Jandaan Fault which acts as back thrust of Main Boundary Thrust. Several anticlines, synclines, and overturned folds are mapped which are trending NNE-SSW and are open, close to tight in nature. The overall geometry and behavior of hanging wall structures refer to the presence of a detachment (MBT as Decollement) in the subsurface and thin-skinned tectonics in the study area. Restoration of cross-sections AA´ and BB´ along the hanging wall of MBT shows the amount of shortening of about 2.1 km and 2.4 km and the percentage is 45% and 41.7% respectively. The average shortening percentage in the study area of sections A-A´ and B-B´ along the hanging wall of the main boundary thrust is 43%.