Xe_s-Xe_n热年代学方法  

Xes-Xen Thermochronometry

作　　者：叶先仁[1] 孙明良[1] 

机构地区：[1]中国科学院兰州地质研究所,730000

出　　处：《地质论评》1999年第3期276-281,共6页Geological Review

摘　　要：^(238)U的自发裂变可以形成Xe的部分同位素,^(235)U的热中子照射也可以产生Xe的部分同位素,二者的结合可以用于地质年代学研究,即Xe_s-Xe_n热年代学方法。该方法用Xe同位素比值来表示地质样品的年代,避免了其他方法涉及到的母体和子体绝对含量的测定,使该方法比其他年代学方法更具优点。Xe_s-Xe_n热年代学方法还可以揭示地质体所经历的后期热扰动事件,有望成为造山带研究中的一个有力手段和工具。129Xe,131Xe,132Xe, 134Xe and 136Xe can be partly formed by 238U spontaneous fission. 235U thermal-neutron irradiation may also produce 129Xe and 131-136Xe. The combination of both, i.e. Xes-Xen thermochronometry, can be used for geochronological study. The experimental procedure is as follows. First, mineral preparation is made, which includes choice of 100-150 μm mineral separates, sample irradiation for 3-10 h, stepwise heating, separation of xenon from extracted gas, and determination of the xenon isotopic composition using highly sensitive noble gas mass spectrometer such as MM 5400 or VG 5400. Then, fission xenon ages will be calculated form the ratio of spontaneous fission xenon from 238U to neutron fission xenon from 235U. In this method, the age of the mineral sample is expressed by its Xe isotopic ratio, thus avoiding determining absolute contents of parental and daughter isotopes in other chronological methods. It is superior to other methods in some cases, for example, interference of other nuclei is less, xenon is more easily retained than argon, there is no elemental fractionation between xenon isotopes, five independent fission xenon ages can be obtained, there is no problem about excess xenon, and so on. Xes-Xen spectrum dating can also reveal late-stage thermal perturbation. It will become an effective means in the study of orogenic belts.

关 键 词：惰性气体 Xes-Xen 热年代学 同位素测年 

分 类 号：P597.3[天文地球—地球化学] P597.1[天文地球—地质学]