Tectonic study of Lesser and Sub-Himalayas in Mansehra and its adjoining areas in Northern Pakistan based on geophysical techniques. | [Geological Bulletin of the Punjab University • 2003]

Author(s):

1. M. Rustam Khan: Institute of Geology, University of Azad Jammu & Kashmir, Muzaffarabad, Azad Kashmir, Pakistan

2. Umar Farooq: Institute of Geology, University of Punjab, Lahore, Pakistan

3. Muhammad Zahid Ayub: Institute of Geology, University of Azad Jammu & Kashmir, Muzaffarabad, Azad Kashmir, Pakistan

4. Asghar Ali: Institute of Geology, University of Azad Jammu & Kashmir, Muzaffarabad, Azad Kashmir, Pakistan

Abstract:

The geophysical study has been carried out in Mansehra and its adjoining areas of northern Pakistan to delineates the thickness of the crust and subsurface active and inactive nature of structural elements. The geological model computed by geophysical experiments demonstrated that in study area the crystalline crust of Indian Plate underthrusted beneath the Lesser and Sub-Himalayas from Mansehra to Muzaffarabad and dips towards northeast at an angle of 6o. The study based on geologic gravity magnetic and seismicity data envisage that Himalayan mountain belt formed by the stacking of different thrust sheets. These thrust sheets consist of crystalline rocks and meta sediments of Precambrian age and sedimentary rocks of Mesozoic to Cenozoic age. The model demonstrated that thrust sheets on the crystalline crust of Indian plate moves southward by the development of thrust faults and strike-slip faults. The continental collision and northward underthrusting of Indian crystalline crust are responsible for the formation of these faults. The model depicted left lateral strike-slip Jhelum fault (JF) near Muzaffarabad which is trending in NW-SE and dips 79o SW. The seismicity slickensides, offset and course sedimentary breccia between Balakot and Muzaffarabad suggested that JF is tectonically active. This study also suggested that Main Boundary Thrust (MBT) does not extend from Rara (Muzaffarabad) to Balakot. In the southwestern part of the study area PT brings the Tanol Formation of Cambrian age over the Hazara slates of Precambrian age. The model depicted the PT near Ghari Habibullah Bridge. The fault plane of PT is steeper near the surface and become gentle in depth and joins the low angle detachment. This study also suggested that Sandogali fault which is depicted in west of Abbottabad is actually the SW ward extension of PT. On the basis of geophysical experiment it is envisaged that PT is tectonically inactive between Sandogali and Balakot. Like MBT and Nathiagali Fault (NT), JF cuts the PT in the north of Balakot. The model computed 52 Km thick Indian plate (crust) under the Mansehra and 55 Km under Muzaffarabad. The thickness of crust increases towards northeast due to the bending of Indian crystalline crust and stacking of different thrust sheets. The seismicity folding faulting and landsliding along the boundary between Lesser and Sub-Himalayas indicates that MBT is tectonically active. This study also indicates a thin sedimentary layer in Brarkot area.

Page(s): 55-63

DOI: DOI not available

Published: Journal: Geological Bulletin of the Punjab University, Volume: 38, Issue: 1, Year: 2003

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