Stress And Strain Analysis For Determining The Deformational History Of Exposed Outcrops Along Bagnotar Baragali Section, Abbotabad, Pakistan

Abstract

The current study focuses on the deformational history concluded form the interplay of strain and stress associated within the folded strata exposed along the Bagnotar-Baragali Section, north Pakistan. A field-based approach is combined with the lab analysis for interpreting the relation of stress and strain. Detailed fieldwork is conducted and collectively twenty different oriented samples are collected from the folded units exposed in the study area. Strains markers i.e., Ooids are studied from shape and orientation for deducing the strain ellipsoid or ellipse through computer generated model by Ellipse fit application. The finite strain of rocks having fabric that indicates history of deformation associated with the rocks. Stress is calculated from field dataset also interpreted and correlated with the deformational history. The Rf/ϕ plot method is used for the ellipticity measure. The strain ratio R and orientation f of the heavily deformed elliptical ooids are summarized and interpreted. The variations are fewer than 90 degrees. The region's strain ratios and angular strains are defined by a mean orientation 25.60 regarding true north and maximum shortening observed is 19.50% calculated from oriented samples having ooids as strainmarkers . The results further show that, the direction of deformed elliptic ooids observed in the SamanaSuk Formation represents the region's stacked tectonic processes. The Rf/Phi model plot is helpful in determining the modification of bedding horizontally and vertically damaged elliptical ooids. Microscopic to mesoscopic structural shortening are parallel to the local tectonic fabric. The intermediate stresses acting on the formation are NE-SW directed. The NEE-SWW directed stresses are minor stresses acting on the formation. While majority of the fractures are oriented in NW-SE direction, while minimal number of fractures are oriented in NE-SW direction. Folding which is observed in the SamanaSuk Formation of Jurassic age which is exposed along bagnotar baragali section as the magnitude of stresses increases deformation exceeds maximum ductility limit and fractures are produced.