Stratigraphic and Structural Interpretation of Tarbela and Gandaf Area to Revise Stratigraphy and Develop Improved Geological Map of the Area, Southwest Hazara Region, Pakistan

Abstract

To understand the geologic and tectonic history, this study aims to do stratigraphic and structural interpretation of the Tarbela-Gandaf area of Khyber Pakhtunkhwa, Pakistan. The study area lies in the hanging wall of two major faults, Baghdarra and Darband Faults. The hanging wall of Baghdarra fault carries the rocks of NW Gandghar Range while rocks present along Darband Fault are of SW Tanawal Ranges. These two Ranges are demarcated here by river Indus. This study aim to do the geological mapping to understand the spatial trends of various stratigraphic horizons and on basis of this to establish the structural configuration of Gandaf and Tarbela area using the stratigraphy. Stratigraphic characterization of road side formations has been done at different locations to reconstruct the stratigraphy. Ultimately a composite stratigraphic column has been developed for regional correlation of constituent lithologies. The stratigraphy of the area is comprised of the Gandaf, Manki, Sobrah and Tanawal Formations. Manki and Gandaf Formations are divided into further units. Folds and Faults structures and contacts between lithological units were mapped using hand-held GPS, compass bearing through compass intersection method during four sessions of fields, then plotted geological observation on the base map to develop the geological map of the area. The study area is divided into three structural subdivision on the basis of major fold structure, these are Gari-Maira Syncline, Topi-Giki Syncline and Sherwal Syncline. All three synclinal fold structures are asymmetrical NE trending with minor drag folds on their limbs and Sherwal Syncline is verging in NW direction. A tectonic evolution model of the study area has been proposed in which the events related to Late Precambrian orogeny (~870-550 Ma) to Himalayan age orogeny (∼65-45 Ma) has been discussed. It is found that the thrusting during Himalayan orogeny is responsible for the current stratigraphic position of the area. The origin of Baghdarra and Panjal and Darband Faults have also been discussed.