PALEOSTRESS AND OUTCROP FRACTURE ANALYSIS ALONG HIMALAYAN FOOTHILLS (EASTERN SALT RANGE), POTWAR PLATEAU, NW HIMALAYA, PAKISTAN

The Salt Range (SR) is an ENE-WSW trending fault bend fold that form the range front of the Himalayan fold and thrust belt in Pakistan. The research is carried out in the Eastern Salt Range (ESR) with the objective to determine the paleostress inversion from reduced stress tensors by using fracture data. The surface morphology of the fold is predominantly shaped by Eocene limestone that provide best exposure of joint surfaces that can be used for kinematic and dynamic analysis. We adopted a classical circle inventory method in the field and collected orientation data (dip amount, direction, and strike) from 7 localities (outcrop stations) of the Eocene Sakesar Limestone. Three prominent fracture trends are present in the study area namely, FS-1; (E-W), FS-2; (ENE-WSW) and FS-3; (NNE-SSW). For stress analysis and data processing we used the Tensor Program of Delvaux and Sperner (2003) and calculated seven stress fields by the Right Dihedron Method. The orientations of the principal stress axes (sigma 1, sigma 2, sigma 3) and Stress Ratio (R) depicts sigma 1(Shmax) and sigma 2 are sub-horizontal while sigma 3 is vertical in all stress tensors. The paleostress results show that sigma 1(Shmax) oriented NNE-SSW belonging to a compressive regime. It is suggested that sigma 1 developed more or less perpendicular to the trend of SRT and other relevant structures in the Potwar Plateau.

Automated summary

The research in the Salt Range area focused on determining the paleostress inversion from fracture data collected from Eocene limestone. The stress analysis showed that the primary stress axes were sub-horizontal and vertical, indicating a compressive regime with the main stress orientation NNE-SSW.