Strike‐slip faulting in a foreland fold‐thrust belt: The Kalabagh Fault and Western Salt Range, Pakistan

The 120‐km‐long Kalabagh fault zone is formed by transpressive right‐lateral strike‐slip along the western Salt Range‐Potwar Plateau allochthon in northern Pakistan. Lateral ramping from a decollement thrust along an Eocambrian evaporite layer produced NNW‐ to NW‐trending folds and NE‐ to N‐dipping thrust faults in a topographically emergent zone up to 10 km wide. Piercing points along the main Kalabagh fault indicate 12–14 km of middle to late Quaternary right‐lateral offset. The older right‐lateral Surghar fault displaced axes of frontal folds of the eastern Surghar Range by 4–5 km. Total displacement is reduced northward in the Kalabagh fault zone where north‐dipping thrust faults splay to the west. Cumulative right‐slip offset in the Kalabagh fault zone is comparable to displacement along the Salt Range frontal thrust, at a minimum average displacement rate of 7–10 mm/year near the Indus River since 2 Ma. In the basement, which dips 2–3° north along the Kalabagh fault, a NNW‐trending discontinuous ridge beneath the lateral ramp is interpreted from residual gravity anomalies. The eastern flank of this basement ridge probably ramped allochthonous strata upward from a depth of over 5 km in the Kalabagh fault zone. Kalabagh faulting displaced and uplifted Holocene terrace deposits and shifted the course of the Indus River eastward. A high slip rate and associated seismicity indicate that the Kalabagh fault zone should be considered active and capable of earthquakes.