雅鲁藏布江大拐弯地区末次冰期以来的冰川活动证据及其构造—环境意义

本文重点讨论雅鲁藏布江大拐弯入口地区末次冰期以来冰川活动的地貌学、14C和10Be定年结果及其构造—环境意义。在海拔3,200m的观景台发现距今24～18ka的冰砾阜,说明末次盛冰期时大拐弯入口地区有大规模的冰川下移现象,并阻塞了雅鲁藏布江主河道,形成堰塞湖,暗示雅鲁藏布江在末次盛冰期时已经下切到与目前接近的深度。在海拔3,150m的打林村阶地,其4级阶地上的砾石10Be暴露年龄显示该阶地形成于距今9.0～8.7ka的末次冰期与新冰期之间的间冰期,意味着这一期间则隆弄冰川再次下移导致阻江。近60年来则隆弄冰川3次跃动,两度阻江,是20世纪3次气候突变的表征。雅鲁藏布江大拐弯入口地区末次盛冰期以来的冰川进退历史对气候变化有良好的指示作用,该历史与大拐弯入口地区的构造地质背景有密切的联系。

Evidence for glacial movement since last glacial period in the Great Canyon, Yarlung Zangbo, SE Tibet and its tectono-environmental implications

Based on new evidence for movement of the Zelongnong glacier since last glacial period in area of the entrance of Great Canyon,Yarlung Zangbo,the paper reported recent results of study on geomorphology,cosmogenic chronology(14C and 10Be)and its implications on tectono-environmental evolution.A 14C age about 18-24 ka from the kame at Guanjingtai(asl.3,200 m)showed that there was a large-scale glacial moving down to the Yarlung Zangpo,blocked this river and formed a checked-up lake.The thick deposits in the lake suggested that the incision depth of the Yarlung Zangpo during that time might be closed to the present depth.The cosmogenic exposure data of boulders from the T4 terrace at Dalin village(asl.3 150 m)showed that T4 formed 8.7-9.0 ka ago,an interval period between the last glacier and the newer glacier,which meant the Zelongnong glacier migrated down again and redamed the Yarlung Zangpo.The glacial relics could be observed from outcrops along Yidian to Longbai villages.In the recent 60 years,the Zelongnong glacier moved forward for 3 times and blocked the Yarlung Zangpo for twice,which might be corrsponding to sudden changes in climate for three times during last century in the Qinghai-Tibetan plateau.To sum up,the history of the glacier development in entrance area of the Great Canyon,Yarlung Zangbo should have a good response to climate change and regional tectonic evolution in the Eastern Himalayan Syntaxis.