雅鲁藏布江中游晚更新世古堰塞湖群的时空关系探讨

Discussion on spatio-temporal relationship of late Pleistocene dammed palaeo-lakes at the middle Yarlung Tsangpo River

雅鲁藏布江中游堵江事件多发,探索堵江事件之间的关系对理解河流地貌演化有着重要作用。在中游宽谷地区,众多河流堆积阶地中保存着古堰塞湖相沉积物。前人对林芝地区、泽当宽谷和日喀则宽谷的古湖相沉积进行了较为深入的研究,三个宽谷在晚更新世均发育过古堰塞湖,但三个地区古堰塞湖之间的时空关系仍未可知。在上述基础上,对雅鲁藏布江中游不同河段古堰塞湖的坝体位置、成因、海拔及发育年代等进行总结分析。归纳出在雅鲁藏布江中游宽谷河段分别发育着3个独立的古堰塞湖,成因多为冰川/冰碛物堵江。晚更新世不同河段降水和地貌条件差异,冰川规模变化速率不同,可能导致冰川前进壅塞河道时间不一致;但3个古堰塞湖的消亡时间较为接近,其溃决过程可能存在关联。

Yarlung Tsangpo River is easily dammed,and the relationship between damming events are important for understanding the evolution of the landform in the valley.Many lacustrine are exposed in the terraces in the middle Yarlung Tsangpo valley.Lacustrine terraces in the broad Mailing,Zetang,and Xigazêvalley are studied,which indicated dammed palaeo-lake occurred during late Pleistocene in all three broad valleys.However,the spatio-temporal relationship between three palaeo-lakes remain unknown.Based on previous studies,herein analysis the dam locations,genesis,elevations,and ages of the palaeo-lakes.During late Pleistocene,three independent separate dammed palaeo-lakes happened in the middle Yarlung Tsangpo River.They are Gega palaeo-lake(3180 m a.s.l.)in the broad Mailing valley,Jêdêxoi palaeo-lake(3585 m a.s.l.)in the broad Zetang valley,and Dazhuka palaeo-lake(3811 m a.s.l.)in the broad Xigazêvalley and the Dazhuka-Yueju gorge.It’s likely advance of glaciers have dammed the Yarlung Tsangpo River during late Pleistocene.The advance rates of the glaciers are different due to the geomorphological difference and the precipitation decrease from Nyingchi to Xigazê,and the time of dam formation were different.The Gega palaeo-lake was dammed by the Zelunglung Glacier at the entrance of the Yarlung Tsangpo Gorge.The Jêdêxoi palaeo-lake was probably dammed at the entrance of the Gyaca gorge.On the contrast,the Dazhuka palaeo-lake was likely dammed at the outlet of the Dazhuka-Yueju gorge.However,the extinction age of three dammed palaeo-lakes were similar(about 13 ka),indicate strong relationship between the failure events.