昆仑山垭口地区“望昆冰期”冰碛宇宙成因核素^(10)Be测年  

Terrestrial Cosmogenic Nuclide ^(10)Be Exposure Ages of the Samples from Wangkun Till in the Kunlun Pass

作　　者：陈艺鑫[1] 李英奎 张梅[1] 张敬春[1] 刘耕年[1] 

机构地区：[1]北京大学城市与环境学院,北京100871 [2]Department of Geography,University of Tennessee,Knoxville,TN 37996,USA

出　　处：《冰川冻土》2011年第1期101-109,共9页Journal of Glaciology and Geocryology

基　　金：国家自然科学基金项目(40971002);国家重点基础研究发展计划(973计划)项目(2005CB422001)资助

摘　　要：昆仑山垭口地区是东昆仑山现代冰川作用中心之一,在第四纪冰期间冰期旋回中保留了多套较为完整的冰川沉积.位于垭口盆地西侧山脊上的望昆冰碛,是本区已知最老的冰川沉积.应用宇宙成因核素10Be暴露年龄方法对望昆冰碛进行年代测定,5个样品中有4个介于(56.9±5.6)～(38.2±3.5)ka BP之间,相当于MIS3阶段,明显年轻于前人所测ESR和古地磁年代,且与地貌系列不符.这一结果不能代表望昆冰碛的实际年代,而应为所测漂砾后期暴露的年代,反映了MIS3阶段昆仑山垭口地区曾遭受过强烈地表剥蚀过程.望昆冰碛10Be暴露年龄显著地年轻,表明应用宇宙核素暴露年代测定冰碛物形成时代具有复杂性,应充分考虑后期剥蚀等地表过程,并应使用其他测年方法进行相互验证.Understanding the tectonic and climatic history of the Tibetan Plateau is crucial for studying the regional and global climate systems,particularly the initiation and chronology of paleo-glaciations.Terrestrial cosmogenic nuclide（TCN） exposure age technology provides a tool to re-examine the glacial chronology and landform evolution in the Tibetan Plateau. The Kunlun Pass is one of the great glaciated areas in the East Kunlun Mountains.A sequence of glacial tills is preserved in this area,and the Wangkun till is the oldest one among them.Four of the five 10Be exposure ages of the samples from the Wangkun till range from（56.9±5.6）ka BP to（38.2±3.5）ka BP,corresponding to the MIS 3.These dates are far younger than the ESR and paleomagnetism ages,and they are inconsistent with the geomorphic appearance and sequence.They do not reflect the deposition of the Wangkun till.They may indicate that the Kunlun Pass experienced intense degradation and denudation processes during the MIS 3. The feature that most of the 10Be exposure ages of the samples from the Wangkun till are within the MIS 3 is typical for cosmogenic nuclide exposure studies in Tibet.It is caused mainly by successive exhumation of the moraines during the MIS 3.The large temperature fluctuation and plenty precipitation during the MIS 3 accelerated exhumation and led to an accumulation of boulders of age from 38 to 57 ka.At the same time,the exhumed materials deposited in the lower catchments of the Golmud River and formed the extreme thick Sanchahe formation. The notably younger 10Be exposure ages of the samples from the Wangkun till not only suggest that the TCN exposure age is deeply influenced by the later denudation process,but also show the limitations of using single method for dating.As a result,detailed field investigation on landform and sediments,together with multi-dating-methods are necessary for establishing the Quaternary glacial sequences.

关 键 词：昆仑山垭口 望昆冰期 10Be暴露年代 MIS3阶段 地表剥蚀 

分 类 号：P597[天文地球—地球化学]