3D structural Model of Eastern and Central Salt Range, Pakistan. A Case Study from Kallar and Surrounding Areas

Abstract

The research work is carried out in vicinity of Salt Range, Pakistan. It marks the outer boundary of Himalayan deformation in Pakistan. In Salt Range strata ranging from Precambrian to Recent, is thrusted along Salt Range Thrust over youngest sediments of Punjab plain. Previous models proposed that the Salt Range evolution is related to simple fault bend fold geometry corresponding to thin skinned tectonics. Various 2D geological cross section are constructed from Main Boundary Thrust in north to Salt Range Thrust in south to confirm the geometry of fault bend fold however no practices were observed for 3D structural interpretation of the Salt Range Thrust. Extensive field visits are carried out to obtain field data for compilation of the revised geological map of the study area at 1:50,000 scale. The stratigraphic successions are grouped on the basis of ages into various groups that aided in understanding the structural evolution of the study area. Four north-south oriented geological cross sections are constructed with the help of field data, seismic lines and well data. The geological map and the cross sections are then incorporated to a 3D model using Midland Valley Move software. The resultant 3D structural model in this research suggests that the Salt Range Thrust emanating from the basal detachment ramps upsection across pre-existing normal fault in the basement. The Salt Range Thrust terminates in subsurface with tip line buried under the hanging wall ramp of the anticline or under the resent deposit of Punjab plain. Absence of fault zones along the previously proposed trace of the Salt Range Thrust also support this idea that Salt Range Thrust act as blind thrust along most of its trend. The presence of series of anticlines and synclines in the crestal portion of hanging wall shows that geometry of the Salt Range differs from ordinary fault bend fold geometry rather it could be best explained as multi bend fault bend fold. It is concluded that Salt Range is evolved as multi bend fault bend fold along blind thrust (Salt Range Thrust) with staircase trajectory.