祁连山西段酒西盆地区阶地构造变形的研究

THE LATEST QUATERNARY TECTONIC DEFORMATION OF TERRACES OF JIUXI BASIN IN WEST QILIANSHAN MOUNTAINS

对祁连山西段酒西盆地晚第四纪阶地的研究表明，该区早第四纪以挤压褶皱、逆冲为特征的构造变形在晚更新世期间乃至全新世仍继承性地进行着，表现为横穿褶皱和逆断裂带的河流及冲沟阶地面的形成、阶地类型的转变、阶地级数的增多和阶地面被断错或发生拱曲变形．其中祁连山北缘大断裂晚更新世晚期以来的垂直运动速率约为１．９２～２．００ｍｍ／ａ．老君庙背斜逆断裂带在晚更新世初以来的垂直运动速率约为１．１５～２．５６ｍｍ／ａ．白杨河背斜逆断裂带晚更新世初以来的垂直运动速率约为０．３２～０．５８ｍｍ／ａ．

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.