Paleostress inversion and outcrop fracture analysis of the brittle deformation along Main Boundary Thrust (MBT), NW Himalaya, Pakistan

Abstract

Fractures are the prominent deformation-induced structural features that develop in the rocks under brittle regime. Establishing a relationship between structural development and paleostress orientations is thus necessary to propose the comprehensive tectonic models of the study area. The study area lies in Lesser Himalaya (LH), which is restricted by the Main Central Thrust (MCT) in the north while the Main Boundary Thrust (MBT) lies south of it. This study aims to analyze the fracture pattern in the rocks along the Main Boundary Thrust (MBT, NW Himalaya, Pakistan) and perform paleostress analysis. Fifty different circle inventories were drawn in the field and 550 individual fracture orientations were observed and recorded. The data obtained includes orientation (dip amount, direction and strike) of fracture planes, density in terms of abundance within the definite area and fracture filling material within the circle. The fracture data is then interpreted through Win-Tensor program for paleostress inversion. It is a computer interactive program based on Right Dihedron Method for fracture analysis and paleostress reconstruction. The results demonstrate a compressive tectonic regime with ~NNW–SSE trending σ1. It is suggested that the Main Boundary Thrust (MBT) is developed almost perpendicular to maximum principal stress orientation.