Joints/Fractures analyses of Shinawah area, District Karak, Khyber Pakhtunkhwa, Pakistan

Abstract

Kinematic compatibility of the western and eastern limbs of the Makarwal Anticline has been studied in the Shinawah and its adjoining area of Takhti-e-Nasrati, District Karak, KPK to understand the propagated structures and general structural model of the area. The study area is tectonically active and observed the deposition of post Pleistocene gravel deposits. In the Shinawah Nala, even younger gravel deposits are present indicating recent to sub-recent tectonic activity. Moreover, the channel avulsion of different nalas in Kurram River also reveals the existence of younger active deformations. Standard procedure has been adopted for the calculation of joint density and their other attitude data. For this purpose, the circle inventory and rectangular method has been espoused. The circle inventory method is valuable where highest numbers of fracture sets are exposed. The obtained data through this could be used for the establishment of their frequency diagrams and statistical density calculations. The shear zones that generally cut across the strata are typical cataclastic strike slip in character showing distinct asymmetric kinematic indicators of redial assemblages (Marwar, 1989). It is observed regionally, where the shear zones cut across each other; evolve a composite geometry of t h e conjugate joint patterns viewing mesoscopic displacements. Tensional joint sets of orthogonal symmetry are well developed. The pattern of these joint sets is observed systematic in nature and may have evolved in response to the forced folding deformational and uplifting phase of the Makarwal Anticline. This fusion of joints and conjugate fractures is properly penetrated on the strata of Dhok Pathan Formation. The general structural trend of the area is north-south. The younger joints are dipping toward east and crosscutting t h e older joint sets developed on the eastern limb of Makarwal Anticline. This frontal faulted limb of the Makarwal Anticline is highly deformed an eroded while exposing the older formations and splays of Surghar Thrust dipping towards west. Thus, we interpret that the origin of the shear zones in the studied area is dynamically related with the neo tectonic of the Makarwal Anticline, while tensional joints are episodically related with the formation and uplifting of the Makarwal Anticline. The synchronous relationship of tensional joints and shear zones further suggests that Makarwal Anticline could be developed as a result of inversion tectonic as positive flower structure under transtensional regime.