Late Quaternary deformation of the Salt Range of Pakistan

Abstract

In the Salt Range, Siwalik strata as young as 400,000 yr B.P. are strongly deformed and overlain with angular unconformity by fanglomerates that are themselves folded and thrust-faulted. The south flank of the Salt Range appears in map view as a series of scallops, convex to the south, produced by a thrust fault bringing the Salt Range south-southeast over sediments of the Jhelum River plain. The western edge of the range is marked by right-slip faults that cut the Kalabagh Conglomerate, which itself rests upon Siwaliks with angular unconformity. The Kalabagh Conglomerate is folded and probably cut by diapirs from the Salt Range Formation. Holocene alluvium appears to be undeformed, and strike-slip fault lineations are more subdued than those along the historically active Chaman fault, suggesting that the recurrence interval of faulting may be measured in thousands of years. The low historic seismicity of the Salt Range may be due to such weak coupling between the Salt Range decollement and crystalline basement that fault displacement is not accompanied by great earthquakes, in contrast to the Indian foredeep of the Himalaya.