雅鲁藏布江中游河谷沉积测年及阶地测量

发布时间：2018-10-08 19:56

【摘要】：雅鲁藏布江位于青藏高原南部,地处喜马拉雅缝合带,是世界上构造作用最强烈的地区之一。同时其中下游地区也是世界上降雨强度最大的地区之一,气候作用同样明显。探讨气候作用与构造作用之间的耦合关系是目前学术界讨论研究的热点。雅鲁藏布江独特的地理环境是研究该问题的理想野外实验室。关于喜马拉雅东构造节加速隆升的时间和雅鲁藏布江巨型裂点形成并长期保持稳定的机制一直存在着巨大的争议。过去对地壳隆升的研究主要通过低温热年代学来完成。而目前正在实施的雅鲁藏布江中下游钻探勘测工作,为雅鲁藏布江的研究工作带来了新的契机。钻孔资料揭示出雅鲁藏布江中游宽谷段谷底沉积厚度超过700 m,其淤积历史和内容远远超过前人的想象。本文通过对河谷谷底沉积物的宇宙成因测年工作为南迦巴瓦地区地壳的隆升提供了全新的年代学证据。测年结果显示,大约从2~2.5个百万年以来,南迦巴瓦地区开始加速隆升,并导致了其上游河谷谷底的沉积和下游区域的强烈下切的开始。冰川堵江是另外一个保持裂点稳定和导致下游河道加速侵蚀的重要因素,笔者使用差分GPS对雅鲁藏布江中下游河段从加查开始直至加拉村的一系列阶地进行了实地测量和考察。对测量数据进行差分处理后,得到了精度可达分米级的剖面连续高程数据。根据阶地实测数据,将中游河段分成三段,第一段加查至朗县,发育河流相阶地。第二段朗县至大度卡段,发育湖积阶地和河流阶地。第三段大度卡至下游,发育河流相阶地,顶部阶地河拔高度较高,反映河流的强烈下切作用。结合对湖相沉积进行的分析,推测出雅鲁藏布江最高一期古堰塞湖的范围。结果显示,该期堰塞湖范围为雅鲁藏布江中下游段从朗县到裂点处的大度卡附近。为末次盛冰期则隆弄冰川冰进堵塞雅鲁藏布江形成的堰塞湖。研究结果显示地壳隆升的构造作用和气候因素导致冰川堵塞共同影响着雅鲁藏布江的演化过程。
[Abstract]:Located in the southern part of Qinghai-Tibet Plateau and located in the Himalayan suture zone, the Brahmaputra River is one of the most tectonic regions in the world. At the same time, its middle and lower reaches are also one of the regions with the highest rainfall intensity in the world. It is a hot topic to discuss the coupling relationship between climate and tectonism. The unique geographical environment of the Brahmaputra River is an ideal field laboratory for studying this problem. There have been great controversies about the time of accelerating uplift of the eastern Himalayan structural joints and the mechanism of formation and long-term stability of the giant fracture point of the Brahmaputra River. In the past, the study of crustal uplift was mainly accomplished by low temperature thermochronology. The work of drilling and surveying in the middle and lower reaches of the Brahmaputra has brought a new opportunity for the research of the Brahmaputra. The borehole data reveal that the bottom of the valley in the middle reaches of the Yarlung Zangbo River is more than 700 m thick, and its siltation history and content far exceed the previous imagination. This paper provides a new chronological evidence for the uplift of the crust in the Nangabawa area by dating the cosmic origin of the sediments from the valley bottom. The dating results show that from about 2 to 2.5 million years ago, the Nangabawa area began to accelerate the uplift, which led to the deposition of the valley bottom in the upper valley and the beginning of the strong undercutting in the lower reaches of the valley. The glacial blocking is another important factor to maintain the stability of the fissure point and lead to the accelerated erosion of the lower reaches of the river. The authors use differential GPS to survey and investigate a series of terraces in the middle and lower reaches of the Brahmaputra River from the beginning of Gaja to the village of Gallas. After differential processing of the measured data, continuous elevation data with the accuracy of decimeter level can be obtained. According to the measured data of terrace, the middle reaches are divided into three sections, the first section is checked to Longxian, and the river facies terrace is developed. The second stage of Longxian to Daduka section, developed lake terrace and river terrace. In the third section, the river facies terrace is developed, and the top terrace is high, which reflects the strong down-cutting action of the river. Based on the analysis of lacustrine sediments, the range of the highest paleobarrier lake in Yalu Zangbo River is inferred. The results show that the range of the dammed lake in this period is near Duca from Longxian to the crack point in the middle and lower reaches of Yalu Zangbo River. It is a barrier lake formed by the last glacial period, Zelonong Glacier, blocking the Brahmaputra River. The results show that the tectonic action of crustal uplift and climatic factors which lead to glacial blockage affect the evolution of Yalu Zangbo River.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P512.2;P597.3

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