伊洛瓦底江上游水系形成时代研究——以滇西龙川江为例

研究伊洛瓦底江水系的发育历史对理解青藏高原东南缘的生长具有重要意义,但是长期以来对其形成时代的研究一直比较薄弱。通过研究伊洛瓦底江上游支流的演化可为认识其水系的发育提供重要线索。龙川江是伊洛瓦底江的一级支流,发源于高黎贡山,流经腾冲芒棒盆地。研究表明在上新世时期芒棒盆地曾被一中型湖泊所占据,现代意义上的龙川江并不存在。龙川江在芒棒盆地内同时切割了上新世中晚期和早更新世的火山岩,腾冲地区早更新世火山岩的K-Ar年龄为0.84~1.4 Ma,说明现代龙川江的出现可能不会早于0.80 Ma,由此推测伊洛瓦底江上游水系可能也是0.80 Ma以来形成的。晚新生代以来东喜马拉雅构造结的强烈构造活动可能是其水系形成与演化的动力来源。

Time of the upper Irrawaddy streams: A case study of the Longchuan River, western Yunnan

Abstract: The formation of the Irrawaddy River system was closely associated with the growth of the Tibetan Plateau. Hindered by difficulties in approaching the steep and rugged terrain in field reconnaissance, researchers have failed to clearly understand the formation time of the Irrawaddy River. The formation history of the tributaries of its upper reach can provide important implications for understanding the formation of the modern Irrawaddy River watershed. The Longchuan River which flows through the Mangbang basin in Tengchong area is the first grade tributary of the Irrawaddy River. Studies show that a paleolake existed and the modern course Longchuan River was not formed in the Mangbang basin in Pliocene. The Longchuan River established its modern path after early Pleistocene. This interpretation is based on the channel morphology with which the Longchuan River carved its course through the middle and late Pliocene and Pleistocene volcanic rock coherently. The age of the Pleistocene volcanic rock is about 0.84-1.4 Ma in Tengchong. From the age of the Longchuan River, the authors infer that the modern Irrawaddy River system was built not earlier than 0.84 Ma. The northward propagation of the eastern Himalaya syntaxis might have supplied an important tectonic driver for the landscape evolution of Irrawaddy from late Cenozoic to the present.