雅鲁藏布江大峡谷入口河段最近两期古堰塞湖事件的年龄  

AGES OF THE RECENT TWO EPISODES OF GLACIALLY DAMMED LAKES ALONG THE UPSTREAM OF THE YARLUNG ZANGBO GORGE

作　　者：李翠平[1] 王萍[1] 钱达[2,1] 唐茂云[1] 

机构地区：[1]中国地震局地质研究所地震动力学国家重点实验室,北京100029 [2]中国地质大学,北京100029

出　　处：《地震地质》2015年第4期1136-1146,共11页Seismology and Geology

基　　金：国家自然科学基金(41372211);地震动力学国家重点实验室自主研究课题(LED2013A07)共同资助

摘　　要：在雅鲁藏布江大峡谷人口河段，分布着多级含湖相沉积的阶地，在河床下还埋藏有巨厚的河湖相覆盖层。通过对阶地沉积和河床覆盖层浅部沉积物的光释光和14C测年，初步建立了河谷E部沉积的地层年代学框架，揭示出雅鲁藏布江大峡谷入口河段在末次盛冰期以来至少发育2期古堰塞湖（古堰塞湖Ⅰ，古堰塞湖Ⅱ），其沉积年龄分别为7～9ka、20～30ka，并形成2级连续的海拔高度分别为2906～2956m、3100～3060m的堆积阶地（T1，T2）。古堰塞湖的沉积时间与青藏高原地区末次冰期冰盛期和全新世早期低温事件相对应，推测是南迦巴瓦峰西坡的则隆弄冰川活动形成冰川堰塞坝堵塞河道的结果。古堰塞湖Ⅰ分布范围较小，在大渡卡-米瑞发育湖相沉积，湖尾大致在米林县城附近，沉积厚度5～8m。古堰塞湖Ⅱ发育范围较广，湖相沉积在大渡卡-卧龙均有出露，湖尾大致在朗县附近，最大沉积厚度超过100m。古堰塞湖Ⅱ被后期河流冲刷，可形成1～3级次级阶地。There are many episodes of multiple-level lacustrine terraces along the entrance of the Yarlung Zangbo Great Canyon. Besides, very thick fluvio-lacustrine sediments are buried beneath the cover of the riverbed. Optically stimulated luminescence and radiocarbon dating provide an approximate timeline of upper valley deposits and reveal at least two glacially dammed lake events （ Ⅰ and Ⅱ ） which have deposition ages of 7-9ka （ Ⅰ ） and 20-30ka（ Ⅱ ）, respectively. The recent two episodes of glacially dammed lakes produced two steps of lacustrine terraces （T1 , T2） correspondingly, which are of elevations 2906-2 956m and 3100-3 060m. The formation of paleo-dammed lakes reflects that the Zelunglung Glacier in the west slope of Mt. Namche Barwa had progressively advanced to block the Yarlung Tsangpo River during the early Holocene and the Last Glacial Maximum. The glacially dammed lake Ⅰ has a relatively smaller extent. Its lacustrine sediments are distributed mainly from Datuoka to Mirui with maximum thickness about 5- 8m. Its end is roughly at the south of Milin County. The glacially dammed lake Ⅱ occupies a large area with the end roughly nearby Lang County. Its sediments are exposed from Datuoka to Wolong with maximum thickness about 100m. After the later fluvial erosion, the lacustrine sediments of this lake formed 1 ~3 levels of secondary terraces.

关 键 词：雅鲁藏布江 阶地 光释光测年 古堰塞湖 冰川堵江 

分 类 号：P597.3[天文地球—地球化学]