雅鲁藏布江大峡谷地貌响应时间域的定量计算

QUANTITATIVE ANALYSIS OF GEOMORPHOLOGIC RESPONSE TIME-SCALE OF THE YARLUNG ZANGBO GREAT CANYON

基岩河道流域地区的地貌演化定量化研究在构造-气候-表面过程关系的探讨中具有十分重要的意义。定量化的分析主要关注气候、构造等外在因素以及河流内在调节机制对地貌演化的影响。本文总结了关于基岩河道流域地貌分析的定量方法和模型的研究进展，并利用DL模型对雅鲁藏布江中下游河段进行了演算，结果显示该地区在稳定状态下地貌演化时间域在0．065～0．420Ma之间，反映了该地区快速的地貌演化过程。

The quantitative research of geomorphologic evolution in bedrock channel fluvial landscape plays a significant role in the discussion of the relationship among tectonics, climate, and surface process. The quantitative analysis focuses on external factors such as tectonics and climate and on the influence added by the internal tuning mechanism of the rivers. The research progresses of the quantitative methods and models which focus on the geomorphologic analysis in bedrock channel drainage are summarized in this paper. The DL model is used as the main calculating method, combined with specific regional conditions. The response to the variation of climate and tectonic perturbation are analyzed quantitatively. Response to climate variation or tectonic perturbation,or both ,the landscape changes and the response time scale changes in different zones. The Yarlung Zangbo Great Canyon has the most complicated structure and the most intense rainfall and thus can be used as the best natural laboratory. It is located at the middle of the East Himalayan tectonic core parts. Theresults show that since 0.15Ma the uplift rate of the Grand Canyon region reaches at 30mm/a. It is the fastest uplift rate observed on the Earth. During the same period the Yarlung Zangbo Grand Canyon area has the largest rainfal all over the world. Therefore the quantitative research of geomorphologic response time-scale in the area to tectonic disturbance and climate changes not only can help further understand the landscape evolutionary history, but also has great significance to study the formation of complicated river network in that area. We use the DL model to calculate the middle and lower reaches of the Tsangpo. The results show that the geomorphologic evolution time-scale is between 0. 065 -0. 420Ma,revealing a rapid geomorphologic evolution in the research area on a steady tectonic state. It is between 0. 11 -0.24Ma when the erosion rate is fixed; between 0.09 - 0.27Ma when the uplift rate is fixed; between 0. 065 - 0. 170Ma when the erosion rate is unanimous; and when the erosion only occurred under the nickpoint of river, it is between 0.24 - 0.42Ma. Compared with results in other regions,the geomorphologic response time-scale of the Yarlung Zangbo Great Canyon shows a more quick rate of geomorphologic evolution. Therefore when the river network system evolution and the geomorphologic evolution are studied,the timescale is better to be controlled in millions of years.