CENOZOIC TECTONICS IN THE URUMQI-KORLA REGION OF THE CHINESE TIEN-SHAN

Cenozoic deformation within the Tien Shan of central Asia has accommod ated part of the post-collisional indentation of the Indian plate into Asia. Within the Urumqi - Korla region of the Chinese Tien Shan this occurred dominantly on thrusts, with secondary strike-slip faulting. T he gross pattern of deformation is of moderate to steeply dipping thru sts that have overthrust foreland basins to the north and south of the range, the Junggar and Tarim basins, respectively. Smaller foreland b asins lie within the margins of the range itself (Turfan, Chai Wo Pu, Korla and Qumishi basins); these lie in the footwalls of local thrust systems. Both the Turfan and the Korla basins contain major thrusts wi thin them; they are complex foreland basins. Deformation has progressi vely affected regions further into the interior of the Junggar Basin, and propagated into the interiors of the intermontane basins. No unidi rectional deformation front has passed across the Tien Shan in the Neo gene and Quaternary. An Oligocene unconformity may indicate the time o f the onset of the Cenozoic deformation, but most of the Cenozoic mola sse has been deposited after the Palaeogene. The rate of deposition in basins next to the uplifted ranges has increased since the onset of d eformation. There has been at least about 80 km of Cenozoic shortening across this part of the Tien Shan. Cenozoic shortening is greater in sections of the range further west; these are nearer to the northern m argin of the Indian indenter. Cenozoic compression has reactivated str uctures created by the two late Palaeozoic collisions that created the ancestral Tien Shan. These Palaeozoic structures have exerted a stron g control over the style and location of the Cenozoic deformation.