Structural geometry and geomorphic evolution of the Trans Indus Manzai Ranges, Western Himalayas, Pakistan

Abstract

At the leading edge of fold-thrust belts, structural deformation can either be accommodated by thick-skinned faulting, and development of structural wedges near the mountain fronts, or by foreland propagation into the basins along the detachment, forming thin-skinned structures. Manzai Ranges at the western extremity of the Trans Indus Ranges were chosen as a case study to describe the structural deformation accommodated in the foreland basin and to study the folded mountain front. These ranges also provide an opportunity to compare along-strike structural variations of the Himalayan frontal thrust system. Both surface (field structural measurements and digital elevation model) and subsurface (2D seismic reflection and well) data were integrated to document different structural styles and their corresponding geomorphic expressions. Based on seismic reflection profiles, the results of structural interpretations constrain westward dipping basement (2.5o) at a depth of ∼10 km in the foreland, which dips deeper in the hinterland. In addition, our interpretation shows a basin-wide Eocene-Miocene unconformity that marks the Himalayan orogenic events. The structural geometry of the frontal Surqamar anticline is quantitatively characterized to be detachment fold, while Jandola, Kundi and Manzai anticlines demonstrate staircase geometry and characterized as fault-bend folds. The kinematics of development varies along-strike in the Manzai Ranges as displacement transfers along the detachment from typical fault-bend folding in the Manzai anticline to detachment folding in the Surqamar anticline, forming thin-skinned structures. The results of this study highlight the structural styles and their evolution in the context of active Himalayan tectonics.