東亞地函動力與板塊互動研究─雅魯藏布江流域及其鄰近地區構造地形分布、成因與年代之探討(II)

青藏高原是印度板塊與歐亞大陸板塊碰撞下的產物，此板塊碰撞發生於55 個 百萬年前，至今仍持續不斷的進行中。青藏高原的應變集中在喜馬拉雅山一線， 與幾個東西向分布的斷裂帶上，除了南北向有明顯的壓縮之外，部分地殼向東南 脫逃，在喜瑪拉雅山東側及東南側形成另外一序列南北向與東南向的斷層，本研 究為了解Namche Barwa Syntaxis (NBS) 西側與東側的新期構造活動，故選擇河 階發育良好的兩個區域，作為初步工作的目標，一為拉薩以東雅魯藏布江流域以 及其北側支流尼洋曲河，另一為雅魯藏布江向南大轉彎以後之另一支流--察隅 河。因河階之發育有(1)構造造成地殼抬升(2)海水面造成侵蝕基準下降(3)地震或 極端氣候造成大規模土石流，沈積物堆積後下切形成。本研究之目標即欲探討這 些階地形成的主因，若其與新構造活動相關，進一步的定年工作將可協助瞭解新 構造研究區的活動性。 本計畫配合CREATE 整合型研究計畫第二年工作項目，進行藏東一帶構造地 形的研究，再使用ASTER 衛星影像，並配合地理資訊系統工具軟體PCI ，進一 步判釋地形特徵及生產數值高程模型 (DEM)，雖然目前執行之計畫已有部分成 果，但部份衛星影像品質不佳，仍需增購衛星影像及影像處理軟體。將判釋結果 彙整後鎖定野外調查區域，進而再利用碳十四、熱螢光、光螢光等定年法測定地 形年代，以了解研究區域之地殼變動速率，對藏東之新構造運動有更深入的認識。Tibet is created by continent-continent collision between India and Eurasia, which occurred in 55 Ma. This event is still actively going on. The strain among Tibet concentrates in a few zones, including Himalaya and its northern major sutures. Except for the shortening, the escaping crusts toward east and south in the southeastern Himalaya give significant strike-slip movements. This project aims to the neotectonics in northern and eastern neighboring areas of the Namche Barwa Syntaxis (NBS). Therefore two areas with abundant river terraces are selected as the targets. One is located at middle reach of the Yalu-Zanbo river and its tributary, Ni-Yang-Chu in the eastern area of city Lahsa. The other area is located further downstream to over the big-turn, where another tributary, Cha-Yu river, flows into the Yalu-Zanbo river. There are three general origins to develop river terraces: 1) tectonically uplifting; 2) base-line drop caused by sea-level falling; 3) huge amount of sediments provided by earthquake or extremely high precipitation. This project is going to analyze the origins of the terraces developed in study area and to understand how neotectonics acts over there. This project will collaborate with the other principal investigators in CREATE to work on the tectono-geomorphic features of eastern Tibet. We use GIS software PCI to recognize the features and to produce the DEM by the Satellite ASTER imageries. Although recent work has made some achievements, we still need new and more Satellite imageries and relevant software because the quality of some imagery we have is poor. Field investigation will be conducted when the potential features are identified by the laboratory work. To further derive the rate of crustal movement, dating methods of radiocarbon, optical stimulated luminescence (OSL), and thermo-luminescence (TL) are applied