• 中文核心期刊
  • 中国科技核心期刊
  • CSCD来源期刊
  • DOAJ 收录
  • Scopus 收录

原位U-Th/He同位素定年技术研究进展及其低温矿床学应用前景

Progress of in situ U-Th/He Isotopic Dating Technique and Its Application to Low Temperature Deposits

  • 摘要: 应用传统单颗粒方法对目标矿物进行定年具有较高要求(如U、Th等母体同位素均匀分布),需要耗时的酸溶过程,同时还需进行α粒子射出效应校正。原位U-Th/He同位素定年技术是近年发展起来的一种定年技术,其主要原理是采用激光加热目标矿物,并通过与激光系统连接的稀有气体质谱(Alphachron)和电感耦合等离子体质谱(ICP-MS)分别完成4He和U、Th等母体同位素分析,将4He和U、Th分析结果代入年龄公式计算即可获得目标矿物的U-Th/He年龄。本文阐述了原位U-Th/He同位素定年技术的主要原理、实验测试流程、适用矿物等,重点对原位U-Th/He同位素定年的技术难点和低温矿床学应用前景进行了分析。相对于传统单颗粒方法,原位测试方法解决了两个关键问题:①无需进行α粒子射出效应的校正,提高了定年结果的可靠性和准确度;②能完成母体同位素分布不均匀样品的测试,扩展了U-Th/He同位素定年的应用范围。尽管原位U-Th/He同位素定年技术在侧向加热效应、剥蚀坑体积测定以及标准矿物等方面尚存在一些亟待解决的问题,但已在硅酸盐、磷酸盐、钛铁氧化物等矿物的年代学研究方面展示了良好的应用前景。随着原位U-Th/He同位素定年技术的发展和进步,尤其是硫化物的U-Th/He同位素定年的发展,将为解决低温矿床的年代学问题提供一种新的思路。

     

    Abstract: The traditional single-grain U-Th/He isotopic dating method a uses time-consuming acid dissolution, correction for α-ejection and more requirements on target minerals (euhedral, transparent, no cracks or inclusions). in situ U-Th/He isotopic dating is a newly developed dating technique, which uses extracted 4He from target mineral by laser ablation system and analyzes the 4He and U, Th and other parent isotopes via the Noble Gas Mass Spectrum (Alphachron) coupled with laser system and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The U-Th/He age of the deposits can be acquired by an age calculation formula using the analytical results of 4He, U, and Th isotopes. The principles, analytical processes, and minerals suitable for dating, technique difficulty and application prospect in low-temperature mineral deposits, are presented in this paper. In situ U-Th/He dating technique solved two key problems compared to traditional single-grain method: (1) Correction of α-ejection is unnecessary, improving the reliability and accuracy of dating results, and (2) Overcoming the bias from heterogeneous distribution of parent isotopes (U, Th), enlarging the range of U-Th/He isotopic dating. Although the in situ U-Th/He isotopic dating technique still needs to address issues such as collateral heating, precise measurement of pit volume and standard materials, it has shown itself to be a promising prospect for silicates, phosphates and Fe-Ti oxides. With the improvement of the in situ U-Th/He isotopic dating technique, particularly the U-Th/He isotopic dating of hydrothermal sulfides, this technique will provide a better way to date low-temperature mineralization.

     

/

返回文章
返回