Subsurface geological model of sedimentary and metasedimentary wedge from Mansehra to Battal based on gravity data, Hazara area, Pakistan

Abstract

This study is aimed to delineate the subsurface structural elements using geophysical techniques in the Haraza area of Pakistan. We investigated the Oghi and Battal thrust faults, sedimentary and metasedimentary wedge, and the absolute crustal thickness based on terrestrial gravity data. Unlike seismic survey relying on wave propagation, magnetic survey is based on both attraction and repulsion, and electrical and electromagnetics on induction. The attractive gravity field produces relatively simpler patterns of anomalies, like a series of highs and lows over regions with undulating basements and buried structures. A qualitative interpretation of gravity data reveals a good deal of information. During the collision of Indian and Eurasian Plates, compressional structures were developed in the Lesser Himalayas or northwest of the Hazara Kashmir Syntaxis. The study mainly focuses on the western limb of the Hazara Kashmir Syntaxis. The regional and local Bouguer anomalies were incorporated to delineate the regional structural units. The gravity model is computed through geophysical technique along with profile A-A' from Mansehra to the Battal area that demarcates the blind Oghi Thrust and emergent Battal Thrust. Tanol Formation of Precambrian age demarcates the Oghi Thrust near Kotli Pine while the Battal Thrust is demarcated within the Mansehra Granite of Cambrian to Ordovician age near Battal. Along with the Battal Thrust, fault gouge and breccias have been observed during the field studies. The total thickness of the sedimentary/metasedimentary wedge in the Mansehra and Battal areas was estimated to be 13.6 km and 14.2 km. In comparison, the total thickness of crust in the Mansehra and Battal areas was 51.6 km and 52.2 km, respectively.