青藏高原西北部晚第四纪以来的隆升作用 ——来自西昆仑阿什库勒多级河流阶地的证据

青藏高原的隆升是新生代最壮观的地质事件,关于青藏高原隆升研究一直是地学界的研究焦点.河流阶地的发育记录了丰富的构造运动和气候变化的信息,近年来被广泛应用于构造运动和气候演变的研究,但前人研究的河流阶地基本分布在青藏高原的周缘,阶地的形成可能是气候与构造运动共同作用的结果.本文通过高分辨率卫星影像的解译,在青藏高原内部的西昆仑阿什库勒地区发现了多达七级的河流阶地.对该处河流阶地结构、沉积特征、几何特征的研究表明该阶地是典型的构造成因阶地.野外利用全站仪对河流阶地地貌形态进行了精细的测量,获得了各级阶地的拔河高度分别为4～5m(T1)、9～ 10m(T2)、16 ～ 18m(T3)、28～31m(T4)、45～48m(T5).通过宇宙成因核素10Be测年方法对各级阶地面的暴露年龄进行了测定,获得了各级阶地的形成时代分别为7.7±0.7ka(T1)、32.7±3.lka (T2)、53.6±2.5ka(T3)、115.7±23.2ka(T4)、166.8±10.4ka (T5)、19.5±8.5ka (T6).由此确定了晚第四纪166.8ka以来不同时期的河流下切速率总体介于0.2～0.35mm/yr,该速率代表了青藏高原西北部晚第四纪166.8ka以来的平均隆升速率.

Late Quaternary uplift of the northwestern Tibetan Plateau: Evidences from river terraces in the Ashikule area, West Kunlun Mountain

Uplift of the Qinghai-Tibet Plateau is the most spectacular Cenozoic geological event. Study on the uplift of the Qinghai-Tibet Plateau has been the focus of geologists. River terraces record a wealth of information about tectonic movement and climate change, and have been widely applied in tectonic movement and climate change study in recent years. However, previously studied river terraces basically distributed in the periphery of the Tibetan Plateau, thus the formation of the terraces may be the results from combination of climate change and tectonic uplift. By interpretation of high-resolution satellite images, we found as many as 7 river terraces in the Ashikule basin, West Kunlun Mountain, which lies in the interior of the Qinghai-Tibet Plateau. Study on the structure, sedimentary characteristics, and geometric characteristics of these terraces shows that the terraces here are typical tectonic origin. Geomorphology and topography of the terraces was surveyed with a total station in the field. Survey data show the heights of the terraces are 4~5m (T1), 9~10m (T2), 16~18m (T3), 28~31m (T4), and 45~48m (T5) respectively. Exposure ages of the terraces were determined by cosmogenic nuclide ¹⁰Be dating methods, which are 7.7±0.7ka (T1), 32.7±3.1ka (T2), 53.6±2.5ka (T3), 115.7±23.2ka (T4), 166.8±10.4ka (T5), and 19.5±8.5ka (T6). Combine the heights and ages of the terraces, river incision rates since 166.8ka to now are determined as 0.2~0.35mm/yr. The incision rate of 0.2~0.35mm/yr represents the average uplift rate in the northwestern Tibetan Plateau since 166.8ka.