THE LATEST QUATERNARY TECTONIC DEFORMATION OF TERRACES OF JIUXI BASIN IN WEST QILIANSHAN MOUNTAINS
CHEN Jie LU Yanchou (Institute of Geology, SSB, Beijing 100029) DING Guoyu (Center for Analysis and Prediction, SSB, Beijing 100036)
The Jiuxi basin with several kilometers Cenozoic deposits in west Qilianshan mountains is located in the junction of the Tibet, Tarim and Alashan blocks. It is one of the regions which are characterized by strongly active folding and faulting with NW～NWW trend, where surface thrusts, blind thrusts and active folds are the main structural style.Tectonic deformation since early Quaternary has continued to the present time and is confirmed by warped and faulted stream terrace surfaces, and tilted flood deposits. When the Shiyouhe river and Baiyanghe river have cut into the cores of the anticlines in the basin, different types and numbers of terraces have developed at different sites. The warping of river terraces demonstrates that anticline growth continues.These features obviously result from the intermittent folding and thrusting of the north Qilianshan fold and thrust wedge since the late Pleistocene. Luminescence dating of sediments from these terraces demonstrates that the formation periods of terraces of Shiyouhe, Baiyanghe and Dahuanggou are at about 90, 70, 44, 29, 20, 13 and 5.6 ka B.P. respectively. Amplitude and rate of terrace uplift are estimated, which represent the cumulative uplift rates of the fold and thrust belts. The uplift rates are larger near by the Qilianshan mountains than far away from it.