NEOGENE TECTONIC AND DRAINAGE EVOLUTION OF THE PAMIR INDENTER

The Pamir arc formed as northwestern India punched into Asia in the last ten milion years. At least 400 km of northward movement occurred along its bounding faults, accompanied by uplift of over 5 km (over 3 km since the early Pliocene). This tectonic activity had enormous effects on the drainage patterns. The complicated river courses of the western Pamir where frontal folding dominates, can be contrasted with the eastern Pamir, where transpressional faulting dominates. Present river gradients, knickpoints, and relic features (like wind gaps- surprisingly still present) indicate that major changes in drainage have transformed originally longitudinal river systems into transverse systems.For example, the Pyandzh river first flows westwards, then cuts across almost the entire Pamir range, before turning westwards into the Amu Darya. Its original southwesterly course can be traced in wind gaps and drainages into the Hari Rud system of Afghanistan. However, its northward segment, though it cuts across existing structures, also follows a subcrustal geophysical contact related to subduction, and which is not expressed in the present surface geology. The effects of climate (possible Pamir plateau ice cap) and local effects (landslide blocking of the Murghab to form Lake Sarez)must also be considered.