Tectonic development of potwar plateau and the saltrange (NW Himalayas, Pakistan)


Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Geological Engineering, Turkey

Approval Date: 2018

Thesis Language: English

Student: Abdul Qayyum

Supervisor: NURETDİN KAYMAKCI

Abstract:

Collision and indentation of the Indian Plate into the Eurasian Plate gave way to the development of Himalaya Orogen since early Eocene (around 50 Ma ago). The most recent products of the Himalayan orogeny is expressed by the development of Potwar Plateu and the Saltrange in W Himalayas, which are the main topic of this thesis. In order to unravel present architecture, evolution, and deformation styles of the Potwar Plateau and the Saltrange we have conducted paleomagnetism, fault kinematics, seismic interpretation and cross-section blancing tehniques. For paleomagnetism more than 1000 samples are collected at 86 different locations spanning from Oligocene to Pliocene sedimentary units to determine vertical axis rotations. Temporal constrains of vertical axis rotations are determined by using magnetostratigraphy. The results have shown that the study area has experienced 10 to 30 degrees of counterclockwise rotations in two different episodes. For understanding the structural development of the study area, paleostress inversion technique is used based on fault slip data collected from the mesoscopic faults developed in the region while Anisotropy of Magnetic Susceptibility (AMS) study was conducted on the collected paleomagnetic samples. These kinematic results show two major deformation phases. During first phase, the horizontal component of major principal stress axis (σ1) was subhorizontal and oriented NNE-SSW and switched to NW-SE during the second phase of deformation. During these phases minor stress vi axes were sub vertical. The major principal stress directions are almost parallel to the intermediate AMS (K2) axes, which collectively indicate compression and shortening. In order to understand 3D architecture of the study area (20) 2D seismic sections that makes up 400 kms line length are interpreted. The interpreted sections are used as balanced cross-sections and restored to determine differential shortening amounts in Potwar and the Saltrange. The restored sections indicated that only 18% of Indian Plate convergence is taken up as shortening in Potwar and the Saltrange, the remaining 82 % convergence is not reflected in the form of shortening possibly due to tectonic glide over salt, also taken up by major thrust faults in the region.