雅鲁藏布江下游地区地质构造特征

喜马拉雅山脉东西两端遥相对应的南迦巴瓦峰(7756米)和南迦帕尔巴特(Nanga-parbat 8125米)分别位于雅鲁藏布江和印度河大转弯的内侧,并分别组成“缅甸弧”和“结罗姆弧”的核心,但是二者实际上可能并不是真正相等的。至少就雅鲁藏布下游地区来说事实上并不存在一个真正的弧弯,而是一个比简单的弧弯要复杂得多的构造区。

A PRELIMINARY NOTE ON THE TECTONIC FEATURES OF THE LOWER YALU-TSANGPO RIVER REGION

Based on field observations in the years of 1973-1974 and other available data, the rocks exposed in the Lower Yalu-Tsangpo River region may be divided into two parts. The Lower, named the Miri group, consists mainly of Paleozoic metamorphosed sedimento-volcanic series; the Upper, named the Namche Bava group, comprises highly metamorphosed and strongly deformed basic volcanics, clastic rocks and a minor part of carbonatites. Faults trending northeast are well developed and intensely compressed. It is assumed that the metamorphism and deformation of the rocks in this region was caused by the northward drift and the subsequent tremendous collision of the Indian plate against the Eurasian plate.The eastern border of the area considered is discussed somewhat in detail. The "Yalu Tsangpo suture", well exposed further west, can be traced eastwards only to the west of the hair pin bend within a fracture zone. Then it reappears along the east side of the Yalu Tsangpo Valley and extends toward southeast down to the eastern slope of Mt. Arakan Yoma, Burma. Along the suture zone, the main rock type is ophiolite, but in the Pakistani Himalaya and on the eastern side of the Yalu Tsangpo Valley it is represented by the "hornblende complex." The relations that the Yalu Tsangpo River bears in its evolution with the geological structures of the region and that between their formation and the northward drifting of the Indian plate are also discussed.