Geomorphologic evidence of phased uplift of the northeastern Qinghai-Tibet Plateau since 14 million years ago
A typical sequence of fluvial terraces and aeolian deposits overlying these terraces were multidisciplinary investigated. New evidences for uplift process of the northeastern Qinghai-Tibetan Plateau in the past 14 million years were obtained. At least 11 river terraces along Huangshui, the first-class tributary of Yellow River, at the Xining-Huzhu region are identified. While the first one (T1) is classified as an accumulation terrace, the others are all basement river terraces, which consist of the Tertiary sandstone and siltstone bedrock, fluvial gravel and pebbles and the overlying aeolian loess-Red Clay deposit. Samples from the aeolian deposits were examined for paleomagnetic stratigraphic reconstruction (1030 samples), luminescence dating (16 samples), magnetic susceptibility and grain-size distribution (more than 4000 samples). The luminescence dating and stratigraphic correlation suggest that terraces of T11, T10,T8, T7, T3, T2, T1 were formed at 14, 11.3, 1.55, 1.2, 0.15, 0.07 and 0.01 million years ago, respectively. Sedimentological analysis and geomorphological observation indicate that formation and evolution of these terraces were mainly driven by tectonic uplift. Therefore, the terrace sequence provides an ideal geological record of the uplift process of the northeastern Qinghai-Tibet during the past 14 million years, and the timings of the terraces formation are regarded as the timings of tectonic uplift. The significant uplifting events took place at 14, 11.3, 1.2 and 0.15 million years ago, respectively. The fluvial incision at the Xining-Huzhu region is less than 100 m during a period of ～12 million years in the Miocene era (between the T11 and T9), while the Huangshui River had incised 432 m during the past 1.2 million years (from T7 to the present floodplain). The river incision process clearly demonstrates that accelerated rising of the northeastern Qinghai-Tibet Plateau during the late Cenozoic, and provides new evidence of previous thoughts. There was a significant readjustment of the fluvial catchment during 1.55-1.2 million years ago: before this time, the paleoriver flowed to southwest. After this time the Huangshui River flows to southeast. A tectonic movement dominates reorganization of this fluvial system.
作 者： Lu Huayu Wang Xiaoyong AN Zhisheng Miao Xiaodong ZHU Rixiang Ma Haizhou LI Zhen Tan Hongbing WANG Xianyan 作者单位： Lu Huayu,Wang Xiaoyong,AN Zhisheng,Miao Xiaodong,WANG Xianyan(State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075,China)ZHU Rixiang(Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)
Ma Haizhou,Tan Hongbing(Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China)
LI Zhen(Department of Geography, Qinghai Normal University, Xining 810008, China)
刊 名： 中国科学D辑(英文版) SCI 英文刊名： SCIENCE IN CHINA SERIES D:EARTH SCIENCES 年，卷(期)： 2004 47(9) 分类号： P542 关键词： river terrace tectonic uplift loess-Red Clay the past 14 million years northeastern Qinghai-Tibet Plateau