矿物中~4He同位素提取和含量测定研究

Study on 4He Isotope Extraction and Quantitative Measurements in Minerals

(U-Th)/He定年是一种有效的低温热年代学定年技术,现已被广泛应用于地质研究的各个领域,而矿物中4He同位素的有效提取和含量准确测定是该技术的关键。磷灰石和锆石是(U-Th)/He定年最常用的矿物,其4He提取条件及铀钍含量测定方法都较为成熟;而其他矿物(如磁铁矿、橄榄石、针铁矿、石榴子石等)的研究则相对较少。文章介绍了当前国内外(U-Th)/He研究中采用的4He同位素提取方法———真空炉加热法和激光加热法,激光加热法因具有低4He背景值和耗时短的优点而成为主要的提取方法。以磷灰石样品测试为例,介绍了成都地质矿产研究所建立的采用激光加热法和四极杆质谱提取4He同位素及其含量测量过程、含量计算和校正方法。指出未来(U-Th)/He测试技术除继续改进现有分析方法外,应加强对更多不同矿物的测试研究。

As an effective low-temperature thermochronometer method, the （U-Th）/He dating technique is currently widely applied in geological research. The efficient extraction and accurate content determination of 4 He in minerals are key for the （U-Th）/He dating technique. This paper introduces the laboratory extraction methods of 4 He in minerals and the 4 He content-determination method in Chengdu Institute of Geology and Mineral Resources. Apatite and zircon are the most common minerals for （U-Th）/He dating, while magnetite, olivine, goethite and garnet are used less for （U-Th）/He dating. There are some routine methods for 4He extraction and U, Th content determination. The resistance furnace heating method and laser heating method 4He extraction from minerals are introduced, and the latter method being more commonly applied because of the fast analysis and low He background. In Chengdu Institute of Geology and Mineral Resources, the laser heating method and the quadrupole mass spectrometer are used to extract and determine the 4He content in apatite. This paper describes the 4He content determination process, calculation and correction method adopted for apatite samples. Furthermore, the alternative minerals should be tested for （U-Th）/He dating to attempt to improve the routine analysis methods.