U-Th/He热年代学原理、测试及应用

U-Th/He年代学方法已经被广泛地应用于地质学研究。特别是由于磷灰石中氦的低封闭温度，该方法对于晚新生代构造、河流和冰川等地表过程非常敏感，具有其他同位素年代学方法无法比拟的优越性。本文回顾了U-Th/He法的发展历史，介绍了U-Th/He法的基本原理、测试方法、α-校正以及U-Th/He法面临的问题，总结了U-Th/He法在新生代构造变形、河流地貌演化、气候变迁和源区示踪4个方面的应用，最后探讨了U-Th/He法未来的研究方向。

Fundamentals,dating and application of U-Th/He thermochronology

U-Th/He method has been widely applied to geological study.Especially the apatite U-Th/He chronometry is sensitive to late Cenozoic structure deformation, and to the geomorphic evolution drove by river incision and glacial erosion because of the low closure temperature of Helium.Therefore the apatite U-Th/He is more suitable than other isotopic chronometry for near surface process of crust.Here we will firstly review the meandering evolution history of U-Th/He method, then introduce the principle, analysis method, α-correction and the facing problems of U-Th/He method, following summarize the four aspects of application of U-Th/He on Cenozoic deformation, on river geomorphic evolution, on climate change and on source tracing, finally look into the future of the method.The fundamentals of the U-Th/He dating are similar to U-Th/Pb dating method, and the difference between these two methods is the radioactive decay daughter.The decay daughter of U-Th/He method is helium, however the decay daughter of the U-Th/Pb is lead.Commonly the dilution method is used to analysize the uranium, Thorium and helium content and then calculate the age of mineral grain.The uncertainty of U-Th/He age by dilution method usually is 5~10 percent.The large uncertainty generally attribute to four factors, i.e. long α-stopping distance effect, unhomogeneous uranium and thorium distribution, helium implanting and helium closure temperature changing resulted from the radioactive damage.Therefore the boring grain-picking has been asked to make sure the mineral grain quality is good enough.In site helium dating by excimer laser is one potential mothed to overcome long α-stopping distance effect and reduce grain-picking work.However larger uncertainty(15 percent or more)of the in site dating method impede the widely application of the helium dating method.The helium has now been applied to a range of tectonic, geologic, geomorphologic, weathering, rive incision, erosion and source tracing problem.Four kinds of application of U-Th/He was presented to illustrate using U-Th/He age.The first one is dating the onset time of northern Qilian Shan exhumation drove by the Tibetan Plateau outgrowth; the second one is dating the evolution of Colorado River Big Canyon; the third one is dating the goethite and studying the climate of Axel Heiberg Island; the last one is tracing the sediment source by U-Th/He and U-Th/Pb double dating.The future of the U-Th/he method was looked forward.Three potential researching aspects were proposed.The three aspects include improving analysis precision, U-Th/He and U-Th/Pb double dating and modeling the geomorphic evolution by combining the U-Th/He age, digital elevation model(DEM) and deformation data.