年轻火山岩氩同位素体系定年技术最新进展及问题  

ACHIEVEMENTS AND LIMITATIONS OF ^(40)Ar/^(39)Ar DATING ON YOUNG VOLCANIC ROCKS

作　　者：杨列坤[1,2] 王非[1] 贺怀宇[1] 桑海清[1] 王英兰[1] 

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [2]中国科学院研究生院,北京100049

出　　处：《地震地质》2009年第1期174-185,共12页Seismology and Geology

基　　金：国家自然科学基金(40221402,40673048,90714007)资助

摘　　要：对年轻(第四纪)火山岩K-Ar法、常规40Ar/39Ar法和激光40Ar/39Ar法定年的优缺点进行了评述,回顾了近10年40Ar/39Ar定年技术在该领域的进展,介绍了惰性气体质谱技术的进步及测量自动化对年轻火山岩定年的影响。讨论了快中子照射及40Ar/39Ar标样问题对高精度年轻火山岩定年的影响,分析了国内用于快中子照射的北京49-2反应堆中子通量梯度问题及对高精度定年的影响。结合年轻火山岩定年及数据处理的实际经验,介绍了年轻火山岩定年中的分析误差、主要影响因素及每个影响因子对总误差的贡献,指出36Ar测试精度、系统本底和质量歧视是影响年轻火山岩高精度定年3个主要内部因素,并给出定量化曲线及减小影响的处理方法。最后列举了年轻火山岩定年存在的问题及可能的探索方向。随着技术的发展,40Ar/39Ar法在晚更新世火山岩定年领域将会占有主导地位。As the requirement of study on paleontology,paleoclimate, magma process,volcanic disasters and paleomagnetism,scientists pay more attention to the young volcanic rocks dating in recent years. In this paper we review the achievements of the ^40Ar/^39Ar dating on young volcanic rocks during the last 10 years,and compare the limitations and strengths of K-Ar,conventional ^40Ar/^39Ar and laser ^40Ar/^39Ar dating methods. As the development of ^40Ar/^39Ar dating relies on the technique improvement,we discuss the influence of the new noble gas mass spectrometer and the full automation of the dating system on the young volcanic dating. Neutron irradiation and flux monitor standard sample are important to get accurate age,so we talk about the neutron flux gradient of Beijing 49-2 reactor which we usually use for sample irradiation and choose the suitable standard for young volcanic sample. We also discuss the analytical error and its sources in detail according to the experience in young volcanic rocks dat- ing. The analytical precision of 36Ar, system blank and mass discrimination are the 3 main internal factors influencing the precise dating of young volcanic rocks. We give two graphs to illustrate the fact and some suggestions to solve this problem. At last,we talk about the problems of ^40Ar/^39Ar dating on young volcanic rocks and what we should do to solve these problems in the future. The improvement of accuracy and precision of ^40Ar/^39Ar dating of young volcanic rocks will make it a more widely used technique and play a more important role in Quaternary geosciences.

关 键 词：第四纪火山岩 K-AR 40AR/39AR 高精度定年 误差分析 惰性气体质谱 自动化 

分 类 号：P597.3[天文地球—地球化学]