Polyphase deformation and control of structural position on lineament distribution in a pop-up fault-propagation fold: Inferences from structural and lineament analysis of the Kambhu anticline, Southern Kirthar Fold Belt, Pakistan

The Southern Kirthar Fold Belt represents the southernmost extent of the active left-lateral transpressional regime between the Indian and Eurasian Plates. This study investigates the structural geometry, deformation history, lineament distribution and the control of structural position on lineament distribution within the Kambhu anticline, a 37 km long and 7 km wide structure located in the frontal part of the Southern Kirthar Fold belt. The analysis is based on geological map (1:253,440), topographic maps (1:50,000) and Digital Elevation Model acquired by Shuttle Radar Topographic Mission with spatial resolution of 30 meters. The Kambhu anticline is a north-south trending, asymmetrical, doubly-plunging, upright, gentle and east-vergent pop-up fault-propagation fold that has undergone two post-folding deformation phases. It was cut across by two antagonistic tear faults, dividing it into northern, central and southern segments. Subsequently, the southern segment was re-deformed by a regional left-lateral strike-slip fault step-over. Lineament analysis reveals that longitudinal lineaments are primarily concentrated along synclinal hinges, while, transverse and oblique lineaments are mainly distributed across the back-limb and hinge zone. Contrary to conventional models, this study identifies a dense population of lineaments in the back-limb, likely associated with the pop-up folding mechanism and post-folding anticlockwise drag induced by post-folding strike-slip faulting. The study highlights the significance of polyphase deformation in structural segmentation and controlling lineament density and orientation in pop-up fault-propagation folds. • The Kambu anticline initially developed as a north-south trending pop-up fault-propagation fold • Subsequent deformation involved modification by two antagonistic tear faults and a left-lateral strike-slip fault step-over • Longitudinal lineaments are concentrated along synclinal hinges, whereas transverse and oblique lineaments are distributed across the back-limb and hinge zone • Lineament distribution is controlled by structural position as well as lithology and erosion • A notably dense concentration of lineaments occur within the back-limb, reflect deformation during both syn-folding and post-folding phases