Tectonic evolution of the Altyn Tagh-Western Kunlun fault system, northwestern China

Neotectonic and structural mapping of the Altyn Tagh and North Altyn faults suggests that Tarim-Tibet relative motion has been distributed across a zone of strike-slip faults with a cross-strike width of at least 100 km. Geologic mapping along the North Altyn fault indicates that Mio (?)-Pliocene motion was predominantly left-reverse. Map relations imply that total offset on this structure is >120 km, since lithologic packages on opposite sides of the fault system do not mach along the entire mapped length of the fault and preliminary 40Ar/39Ar thermochronologic data suggest that this pattern does not reflect late Mesozoic or Cenozoic juxtaposition of different crustal levels.; The width and distributed nature of deformation within the Altyn Tagh fault system requires that a regional marker be identified to determine total offset. Data presented here suggest such a marker exists in the western and eastern Kunlun Shan, which lie to the north and south of the fault system, respectively. U-Pb ion microprobe zircon dating reveals widespread Cambro-Devonian plutonism within both belts. In both cases this Cambro-Devonian magmatic province is sharply bound to the south by the Songpan-Ganzi flysch belt. I suggest that the Altyn Tagh fault has offset the boundary between these two tectonic domains by 475 ± 70 km.; It is unlikely that the present structural framework within the western Kunlun Shan has been responsible for the separation of this belt from the eastern Kunlun Shan. Investigation of the western Kunlun Shan indicates this thrust belt comprises three main south-dipping structures: the Hotan, Tiklik, and Tam Karaul thrusts. Integrated structural and thermochronologic studies of the Hotan and Tiklik thrust sheets suggest that Oligocene to recent deformation of this belt is dominated by thin skinned, north-directed thrusting which is restricted to shallow crustal levels (i.e., <10 km). Both the western Kunlun Shan and the Tibetan plateau to the south move northwards relative to Tarim along this south-dipping thrust system. (Abstract shortened by UMI.)...