Terrace Measuring And Deposition Dating Of Valley In Middle Yarlung Zangbo River

The Yarlung Zangbo river is located in southern Tibet.It is one of the world’s most intense tectonic regions. Also the affect of climate is equally clear in the downstream region. Discussing the coupling between climate and tectonic is the current academic research focus. The unique geographical environment of Yarlung Zangbo river makes it become a natural laboratory in the wild.Yarlung Zangbo river flows through Niagara and Nanjiabawa,and it is one of the most intense erosion valley areas. The time of accelerated uplif of the Eastern Himalayan and the mechanisms for the knick point’s formation and stability have been discussed for a long time.Past studies discuss rock uplift mainly through low temperature heat chronology. The drilling survey work in Yarlung Zangbo river,has brought new opportunities for the research work of the Yarlung Zangbo river.Drilling data reveal thickness of deposition in the bottom of valley Yarlung Zangbo river is more than 700 m, which has a huge amount history and content than previous guess. In this paper we provide new evidence of chronology by test the dating of sediments from valley bottom using cosmogenic dating. Dating results show that since 2 to2.5Ma ago Nanjiabarwa region started its accelerated uplift and resulted in valley deposition in upstream and the strong erosion in the downstream as well.River blockage by glacier is another important factor for the stability of the knick point and the accelerated erosion of the river downstream. I had also did some measurement work of a series of terrace from Jiala to Jiacha using Trimble Geo XH differential GPS. After differential calculation, I got very accurate data of the terraces. Based on these datas, I divided the river to three part:Part 1 is from Jiacha to Langxian. In this part, terraces are all fluvial terraces.Part 2 is from Langxian to Daduka. In this part fluvial terraces and lacustrine terraces exist together. Part3 is from Daduka to the downstream. In this part, terraces appear very high from the river surface.It shows that the river strongly erode the rock.Combined analysis of lake sediment and result of measurement,I infered the highest lake’s range. It is from Daduka to Langxian. The advance of Long Lane glacier resulted the blockage of Yarlung Zangbo riverThe results show that tectonic and climatic factors effect the evolution of Yarlung Zangbo together..