MIOCENE 40AR/39AR AGES FROM THE KARAKORUM BATHOLITH AND SHYOK MELANGE, NORTHERN PAKISTAN, INDICATE LATE TERTIARY UPLIFT AND SOUTHWARD DISPLACEMENT

The magmatic arc of the Karakorum Mountains is separated from the Cretaceous-Tertiary Kohistan arc sequence by an ophiolitic mélange-the Shyok Mélange. Two views of the age of the Shyok Mélange and Karakorum arc are: (a) that they represent a mid-Mesozoic arc-trench complex which collided with the Kohistan arc in the Cretaceous before the closure of the main Tethys ocean to the south; and (b) that they represent a late Tertiary arc-trench complex which closed in the late Miocene, representing final subduction of Tethyan sea-floor. Whether final destruction of ocean crust took place in the Mesozoic or Tertiary has important implications for current models of the development of the Indian-Asian collision zone. Here we wish to report ages of between 20 and 8 Ma, suggesting that final assembly and uplift did not occur until the late Tertiary; and that the Shyok Mélange is the structural equivalent of the Main Central Thrust of the Himalaya to the east. Like the Main Central Thrust, the Shyok Mélange appears to mark intraplate continental subduction which is mainly responsible for Tertiary granitoid intrusion, deformation and uplift in the High Himalaya and Karakorum to the north. © 1990.