Ages and geological significance of the river terrace of Datong River in Qilian Mountains

Qilian Mountains are the key study areas for tectonic deformation and uplift of Tibetan Plateau. Since Early Pleistocene, the river terrace of Datong River has been the record of tectonic uplift and climate changes in Qilian Mountains. Ascertaining the ages and geological significance of the river terrace of Datong River is of great significance in analyzing the regional structure and climate changes in Qilian Mountains. Using ESR dating technique, the authors measured the section samples in Jiangcang Area of Datong River and acquired the rock strata ages, which were (42±4) ka B.P., (71±5) ka B.P., (121±12) ka B.P., (210±20) ka B.P. and (602±60) ka B.P. respectively. According to the dating results, the authors confirmed the section was formed in the environment of fluvial facies deposition, and that its ages were the periods of Jiuquan conglomerate and Gobi conglomerate in Middle and Late Pleistocene. And it showed that the river terrace of Datong River has been formed before 542~662 ka B.P., and that its formation might be influenced by the basin-mountain movement after Miocene Baiyanghe Formation or by the wrinkle deformation in Early Pleistocene in Qilian Mountains. The authors calculated the uplift rate via the dating results, and the results showed that the uplift rate was increasing from the late period of Middle Pleistocene to the middle period of Late Pleistocene, which reflected the enhancement of tectonic movement and climate changes in Datong River Basin and the rapid uplift of Jiangcang Area in Qilian Mountains. These conclusions could provide new proofs for the viewpoint that the northeastern edge of Qinghai-Tibet Plateau has expanded in both area and volume.