Study On The Exposure Age Of ¹⁰Be And ²⁶Al Landslides In Wangbeicun, Southeastern Tibet

The terrestrial cosmogenic nuclides,dating technique(TCN)is a new dating method that developed since the 1980s.This dating method has lots of advantages,i.e.,the used mineral for dating is simple composition,widely distributed,easily chemically treated,and strong resistance to chemical weathering.In addition,the relative longer half-life of 10Be and 26Al enable the upper limit of dating can reach millions of years.As long as the rocks are exposed on surface ground due to landslides,the rocks will receive cosmic rays immediately,and the 10Be and 26Al will be accumulated in the outcrop rocks since then.By measuring the concentration of 10Be and 26Al in the exposed rock can help us to get the exposure age of the landslide.Recently,with the development of AMS technology,the dating method based on TCN(10Be and 26Al)has gradually become one of the effective measures for determination the age of landslides.However,there are still some controversial issues existing in present studies of landslide dating by using TCN method.To overcome these,it is advocated that the dating should be cross-validated by using two kinds of nuclides,and measuring the samples from different positions of the landslide,such as surface of landslide scarp,sliding planes and boulders..In addition,it should take into consideration that the possible effects of erosion rate on the chronology result.The large-scale ancient Wangbei Vallage Landslide,located at the Basu County,Changdu,Tibet,is close to the planned Yasuda Station of the Sichuan-Tibet Railway.The area of the landslide accumulation is the location of the planned Basu station for the planned Sichuan-Tibet Railway.Accurately determining the active years of Wangbei Village landslide will help deepen the scientific assessment of the route selection of Sichuan-Tibet Railway,and at the same time contribute to the risk assessment and management of local landslides and other mountain hazards.It also provides basic data for discussing the causes of landslides.However,so far no scholars have conducted chronological studies on the landslides in Wangbei Village.In this study,the radionuclide exposure dating method is used to determine the exposure age of Wangbei Landslide.Samples were collected from the surface of landslide scarp,sliding planes and boulders.By considering the possible effects of shielding factor and erosion rate,we get the calibrated exposure age of the Wangbei Landslide.The main conclusion are as follows:(1)Assuming that the concentration of the cosmogenic nuclear has reached equilibrium,We calculated the maximum erosion rate by using the 10Be concentration.By comparing the derived maximum erosion rate with those controlled by different factors(i.e.tectonics,lithology,climate,slope,sample in different exposure time scales),its maximumerosion rate is 2.93 mm/ka.And Through the existing rate of granite erosion on the glacier bedrock in the Daocheng area in the southeast of the Qinghai-Tibet Plateau,the erosion of the Wangbei Village landslide rocks may be 0.69 mm/ka.(2)In combination with the chronology result,we infer that the minimum age of Wangbei Vallage Landslide is between 165.12±15.98 ka-193.04±18.71 ka,which nay not less than 174.32±7.99 ka BP.In addition,there may have been another rock-fall event which occurred on less than 28.33±1.78 ka BP.