帕米尔高原东部塔合曼大型滑坡体的 10Be测年

塔合曼滑坡体是发育在新疆帕米尔高原东部1895年塔什库尔干7级地震区北端的一个大型滑坡体,总体呈"舌"形,由崩塌区、滑坡区和堆积区三部分组成,在滑坡区和堆积区分别形成了平行与垂直于滑坡体滑动方向的滑坡体台阶。本文介绍了该滑坡体的基本特征并采用宇宙成因核素测年技术对其形成年代进行了测定,简要论述了该测年技术的基本原理、野外采样原则及样品前处理过程。采自滑坡体不同部位的6个片麻岩巨砾样品的 10Be暴露年龄结果非常一致,表明该滑坡体发生在 6.8±0.2ka,同时也表明了 10Be暴露测年是研究大型滑坡的有效测年手段。结合该滑坡体被慕士塔格断层断错并形成断层陡坎、滑坡体内发育的冲沟规模以及巨砾表面较厚的岩石漆,我们认为该滑坡体并非1895年地震的产物。

10BE DATING OF TAHEMAN LARGE SCALE LANDSLIDE IN EASTERN PAMIR AND PALEOSEISMIC IMPLICATIONS

Large-scale landslides/rock avalanches are significant events that result in erosional degradation of mountains as well as the change of orogenic mass balance,and imperil human populations and their infrastructure.Determining the distribution of landslides through time is the key to assess hazards and for understanding triggering mechanisms,such as climatic change,phases of enhanced earthquake frequency,or post-glacial stress relaxation.However,few studies have been undertaken on large landslides in the high mountains of Central Asia because of the inaccessibility of the region and the associated problems of mapping and sampling for numerical dating.The Taheman landslide is located on the south side of Muztagh Ata(7546m above sea level)just to the north of the 1895 Tashkurgan earthquake(M7)surface rupture in the NE Chinese Pamir,a tectonically active orogen.This paper describes the characteristics of Taheman large scale landslide,with a debris area as 5.1km2 and its volume as 155×106m3(height and width are ca.150m and ca.2km respectively).The landslide is composed of sediment deposit zone,transport zone and detachment zone.Its deposit has a tongue-shaped toe which is marked by numerous sub-parallel,parabolic,and longitudinal ridges.The surface of the deposit is dominated by large,very angular block>1m in diameter.Some blocks almost exceed 20m in length and have jigsaw morphology.Blocks on the surface form an open framework with some sand and fine gravel which is the result of bedrock shattering during transport and emplacement.In order to confine the time of the landslide,six gneiss boulders(length,height and width are all more than 1m)on the surface of the landslides were collected for 10Be exposure dating.All these samples were processed in University of Cincinnati and then measured by accelerator mass spectrometry at PRIME Laboratory in Purdue University.Basic concepts of cosmogenic nuclide dating,sampling and pretreatment are showed in this paper.The six 10Be dating ages are very consistent and indicate their formation 6.8±0.2kaB.P.The consistence suggests TCN exposure dating is an effective method of dating landslides.In addition,gully scale,rock varnish thickness,offset scarp and dating results suggest that the Taheman landslide was not trigged by 1895 Tashkorgan earthquake.Moreover,the methods and parameters used for interpreting TCN data are not yet standardized.Therefore,we attempted to use our six 10Be dating data to set up data reporting standards needed in order to help other scientists to use our data to do more research.