ABSTRACT
Sedimentary basins marginal to the Himalaya and adjacent ranges subsided markedly and continuously from Miocene times onwards, accumulating progressively thicker continental elastics. In contrast, recent radiometric and fission-track dates indicate that the northwestern Himalaya, Karakoram, Pamir and adjacent ranges underwent major phases of erosion (and presumably uplift) starting around 15 myr in the mid-Miocene. These cooling dates seem remarkably consistent in the various ranges north of the Main Central Thrust in India and north of the Northern Suture in Pakistan. In conjunction with the late Tertiary deformation of the northwestern Himalaya and Pamir, this suggests that the late Cenozoic uplift of the Himalaya, Pamir and Tibet is related to the start of intracontinental thrusting along the Main Central Thrust and Northern Suture, after earlier Tertiary telescoping of the northern Indian passive margin and crustal thickening by shortening in Tibet. Sediment budget studies indicate progressively increasing sediment volume delivered to the Indian Ocean and to areas north and west of the mountains in post-Oligocene times by erosion of the rising mountains. These increasing rates of erosion indicated by radiometric and sediment budget studies are confirmed by evidence of rapidly increasing rates of net uplift derived from palaeontological and palaeoclimatic evidence and from river gradient studies. Most of the uplift of the Himalaya, Karakoram, Pamir, Kun Lun and Hindu Kush has taken place in the last 15 myr and cannot be directly related to continental collision. A more plausible mechanism involves changes in upper mantle structure as a consequence of the end of subduction along the Pamir and Himalayan arc.
