汉中罗汉洞宇宙成因核素26Al/10Be埋藏年龄

摘要

汉中天坑群是在我国北纬32°N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300余处.洞穴中保留有丰富的古地下河冲积物、次生化学沉积物等,可能为研究岩溶地下河演化及中国南北方乃至全球古环境及气候变化提供宝贵素材.目前鲜有该区域相关年代学研究成果报道.本研究运用加速器质谱仪(AMS)宇宙成因核素26Al/10Be埋藏年龄测试技术,获得陕西汉中岩溶洞穴罗汉洞内次生沉积石英砾石的埋藏年龄为1.51+1.54/-0.88Ma,初步限定了该地区岩溶洞穴的发育年代,同时获得石英砾石样品埋藏前的流域侵蚀速率为138.9±76.5 m/Ma.中国早更新世中期是一个以温暖气候为主的时期,湿润的热带、亚热带气候和季风气候对中国南方喀斯特景观的形成起关键作用.早更新世中期较高的温度和降雨量可能是陕西汉中地区岩溶洞穴发育的主要原因.早更新世区域构造剥蚀事件为该地区岩溶洞穴发育提供了必要条件.%Hanzhong karst landscape was discovered on the north margin of the moist tropical-subtropical karst landform area of about 32°N in China for the first time.More than 160 karst caves have been surveyed.The findings of abundant ancient underground alluvial deposits and secondary chemical deposits in the caves may provide valuable material for the study of the evolution of the underground karst river,and global and local paleoenvironment and paleoclimate changes.However,no report on the chronology of the Hanzhong karst region has been published until now.In this research,we report acosmogenic nuclides 26Al/10Be burial ages of 1.51 + 1.54/-0.88Ma for the Luohan cave in Hanzhong.We also derived a catchment-scale erosion rate of 138.9-±76.5 m/Ma for quartz gravel samples before the burial.It was dominated by warm climate during middle of the Early Pleistocene in China.The humid tropical,subtropical and monsoon climate played a key role in the formation of karst landscape in Southern China.The higher temperature and rainfall in the middle of Early Pleistocene may be the main reason of karst caves development in Hanzhong,Shaanxi.The regional tectonic denudation event in the Early Pleistocene provided the necessary conditions for the development of karst caves in this area.