汉中大佛洞宇宙成因核素26Al/10Be埋藏年龄

Cosmogenic nuclides ^(26)Al/^(10)Be burial ages of Dafo Cave in Hanzhong, Shaanxi, China

汉中天坑群是在我国湿润热带-亚热带岩溶地貌区北界首次发现的岩溶地质景观,已查明区内发育岩溶洞穴160余处,对研究中国南北方乃至全球古地理环境及气候变化具有重要科学价值。目前该区域地貌演化、岩溶洞穴发育研究刚刚起步,尚没有该岩溶区年代学研究成果报道。本文尝试运用加速器质谱仪(AMS)宇宙成因核素^(26)Al/^(10)Be埋藏年龄测试技术,对汉中南郑岩溶洞穴大佛洞内次生沉积石英砾石进行年龄测定,获得^(26)Al/^(10)Be埋藏年龄为(1.07±0.71)Ma,初步限定了汉中岩溶洞穴大佛洞的发育时期;同时获得大佛洞石英砾石样品在埋藏前该流域侵蚀速率为(156.5±73.4)m?Ma-1。

Background,aim,and scope Hanzhongtiankeng is the karst geological landscape first discovered on the north margin of the moist tropical-subtropical karst landform area around north latitude 32°in China.There are more than 160 karst caves were surveyed and had important scientific value for Chinese and global paleoenvironment and paleoclimate research.But there have not any report on the chronology of the Hanzhong karst region until now.We purposed to determine the formation ages of karst caves in Hanzhong,China.Materials and methods The quartz gravel samples were collected from Dafo Cave in Hanzhong.Quartz purification and target preparation were carried out at Xi’an Accelerator Mass Spectrometry Center of the Institute of Earth Environment,Chinese Academy of Sciences.And then,the cosmogenic nuclides 26Al and 10Be concentrations were measured on 3 MV accelerator mass spectrometry.Results Totally 14.2257 g pure quartz was extracted from the quartz gravel samples from Dafo Cave.Finally,the cosmogenic nuclides 26Al and 10Be concentrations were measured on accelerator mass spectrometry(AMS).And then,the cosmogenic nuclides 26Al/10Be burial age of Dafo Cave and the erosion rate before the quartz gravel samples buried in Dafo Cave was calculated.Discussion The cosmogenic nuclides 26Al/10Be burial age of Dafo Cave reflected that the karst cave in Hanzhong developed in Early Pleistocene probably.The warm and humid paleoclimate in the middle of Early Pleistocene provided necessary condition for the development of karst caves in Hanzhong.Conclusions We first report that the cosmogenic nuclides 26Al/10Be burial age of quartz gravel in Dafo Cave in Hanzhong is(1.07±0.71)Ma.The erosion rate before the quartz gravel samples buried in Dafo Cave is(156.5±73.4)m.Ma-1.Recommendations and perspectives This is a new exploration of dating on Hanzhong karst cave and very important to the research of local landscape evolution,karst evolution,paleoenvironment and paleoclimate.It also shows a well foreground in the geomorphic evolution and karst development research by AMS cosmogenic nuclides dating technology and method.