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A COMPARATIVE STUDY OF STRUCTURAL STYLES IN THE KOHAT PLATEAU, NW HIMALAYAS, NWFP, PAKISTAN.

Ahmad, Sajjad (2003) A COMPARATIVE STUDY OF STRUCTURAL STYLES IN THE KOHAT PLATEAU, NW HIMALAYAS, NWFP, PAKISTAN. PhD thesis, University of Peshawar, Peshawar.

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Abstract

Kohat Plateau is located in the northwestern apex of the southern deformed fold and thrust belt that borders the entire Himalayan foothills in India and Pakistan. Detailed mapping, combined with structural analysis throughout the Kohat Plateau, and critical reassessment of the previously published data have resulted in reinterpretation of the structural evolution of this important part of the active foreland fold and trust belt of Northern Pakistan. The present study within the Kohat Plateau suggests that it is dominantly a thin skinned deformed fold and thrust belt over its major part, superimposed by thick-skinned structures in the south and has been distinguished as the Northern, Central and Southern Kohat Plateau. The thin-skinned structures aer well developed within the outcropping rocks of the Northern and Central part of the plateau and exhibit a variety of structural styles that include macroscopic-ups and triangle zones and relics of a folded thrust sheet. The macroscopic-scale doubly overturned disharmonic anticline folds are well exposed throughout the Northern Kohat Plateau and west of the longitude of the Jatta Ismail Khel in the Central Kohat Plateau. The imbricate fans, pop-ups and triangle zones are well depicted only east of the longitude of the Jatta Ismail Khel of the Central Kohat Plateau. Relics of a folded thrust sheet are observed in the Northern Kohat Plateau alone. The structural style within non-outcropping rocks of the plateau is dominated by a series of thrust splays getting younger towards south from the basal decollement. The motion along these thrust splays give rise to fault propagation folds in the overlying strata. Remarkable structural contrast has been observed within the outcropping and non-outcropping rocks both laterally and vertically and is ascribed to a major rheological change. The thick-skinned structures are confined to a zone (3-12 Kilometer wide) in the south, stetching from Zarwam in the west up to Banda Lakhoni in the east. This zone is defined by a couple of east west trending wrench faults that involve the basement as well, Deformational features related to this fault system include enechelon folds, steep to vertical dips and stratigraphic mismatch across the fault surfaces. The genesis of this wrench zone is related to the westward underthrusting of Kohat Plateau underneath the Sulaiman and Samana Ranges along the ranspressional boundary called as the Kurram Fault. Orientation of both large and small scale structures within the Kohat Plateau indicate that it has undergone deformation as a result of an earlier phase of compressional deformation related to north northwest horizontal compressional stresses with the exception in the southwest. Towards the southwestern boundary of the Kohat Plateau along the Bannu Basin, the earlier compressional structures are overprinted by a later phase of transpersonal deformation. The Kohat Plateau is dominantly a south-southeast vergent structural system impinging upon Bann Basin in the southwest and Punjab Foreland in the southeast. The Surghar Range in the southeast represents the active deformational front of the Kohat Plateau and is interpreted as strong to weakly emergent thrust front along which Paleozoic rocks are thrust southwards over the Punjab Foreland.

Item Type:Thesis (PhD)
Uncontrolled Keywords:tectonic setting, structural setting, kohat plateau, paleozoic rocks
Subjects:Physical Sciences (f) > Earth Sciences(f4) > Geology, (f4.1)
ID Code:391
Deposited By:Mr. Muhammad Asif
Deposited On:03 Aug 2006
Last Modified:04 Oct 2007 21:00

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