Structural Geometry of a Part of the Southeastern Hazara Fold-Thrust Belt, Khyber Pakhtunkhwa, Pakistan

Abstract

 The southeast Hazara forms a part of a fold and thrust belt in the Lesser Himalayas of Pakistan. This paper attempts to address the structural geology of a part of southeastern Hazara and explains the geometry and evolution of various structures present within the Hazara Slates and overlying younger rocks. The study area is covered by Pre-Cambrian and Mesozoic-Cenozoic age rocks that have undergone severe deformation, as illustrated by the development of southeast verging thrust faults and associated folds. The structural evolution of the study area is controlled by the deformation associated with Hazara Thrust Zone which is the major tectonic event and has resulted in thrusting of Pre-Cambrian Hazara Slates over the Mesozoic-Cenozoic rocks. Two discrete phases of deformation have been identified in the area, inferred from the cleavage study in the Hazara Slates. Cleavages in the Hazara Slates include a well developed bedding parallel slaty cleavage 51 which is the result of Pre-Cambrian deformation event. Conjugate sets of cleavages 52 and 53 are also present but are much less developed than the S1. These conjugate sets of cleavages are the result of Himalayan deformation events. It is inferred from the fact that joints corresponding to these cleavage sets are present in the overlying younger carbonates. The general trend of the hinge lines of meso and macro-scale folds observed within the Hazara Slates and overlying younger sediments is northeast-southwest, which is indicative of the fact that the area was mainly subjected to northwest southeast compressive stresses. Our study reveals that Hazara Thrust Sheet plays a pivotal role in the structural evolution of the study area. Dominant slaty cleavage (S1) developed in Hazara Slates indicates Pre-Cambrian deformation event whereas less prominent conjugate cleavage sets (52 and S3) are associated with the subsequent Cenozoic Himalayan deformation event. The east west trending sequences with dominant southeast directed faults depicts that stresses were directed from north-northwest.