地学前缘 ›› 2020, Vol. 27 ›› Issue (3): 123-132.DOI: 10.13745/j.esf.sf.2020.4.13

• “非传统稳定同位素:分析方法、示踪机理和主要应用”主题专辑 • 上一篇    下一篇

铷同位素分析方法及研究进展

张卓盈1,2(), 马金龙1,*(), 张乐1, 曾提3, 刘颖1, 韦刚健1   

  1. 1.中国科学院 广州地球化学研究所 同位素地球化学国家重点实验室, 广东 广州 510640
    2.中国科学院大学, 北京 100049
    3.中国科学院边缘海与大洋地质重点实验室, 广东 广州 510640
  • 收稿日期:2019-06-28 修回日期:2020-02-27 出版日期:2020-05-20 发布日期:2020-05-20
  • 通讯作者: 马金龙
  • 作者简介:张卓盈(1992—),女,博士研究生,地球化学专业。E-mail: zhangzhuoying@gig.ac.cn
  • 基金资助:
    国家自然科学基金项目(41573003);中国科学院广州地球化学研究所135项目(135PY201605);同位素地球化学国家重点实验室技术研发基金项目(SKLaBIG-JY-16-2)

Advances in rubidium isotope analysis method and applications in geological studies

ZHANG Zhuoying1,2(), MA Jinlong1,*(), ZHANG Le1, ZENG Ti3, LIU Ying1, WEI Gangjian1   

  1. 1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
    3. Key Laboratory of Ocean and Marginal Sea Geology, Chinese Academy of Sciences, Guangzhou 510640, China
  • Received:2019-06-28 Revised:2020-02-27 Online:2020-05-20 Published:2020-05-20
  • Contact: MA Jinlong

摘要:

Rb作为一个具有中度挥发性、流体活动性、在岩浆过程中呈不相容性的碱金属元素,能为各种地质过程和物质源区提供制约;同时,87Rb是放射性母体,Rb-Sr定年体系在确定长时间尺度的地质体年龄方面也有广泛的应用。传统研究认为特定地质年代下Rb同位素比值(87Rb/85Rb)是一个定值,但随着分离纯化方法的改进和质谱分析精度的提高,高精度Rb同位素组成得以测定,其结果显示,不同地质样品存在明显的Rb同位素组成的差异,意味着地质过程中存在Rb同位素的分馏。Rb同位素分馏能否为示踪Rb的地质过程提供更多有用信息,是否会对传统Rb-Sr定年体系产生影响,这些基础性的问题目前仍然没有答案。要回答这些问题,首先需要了解不同地质储库的Rb同位素组成,发现不同地质过程中的Rb同位素分馏,探讨其发生的控制机制。然而,这方面的研究目前还非常欠缺。文章回顾了近20年来国际上地球科学领域中的Rb同位素已有的研究,包括技术方法、分馏机理等各个方面,在此基础上对其研究前景进行展望,主要包括:(1)总结了Rb同位素组成测定的化学纯化及仪器测量方法,并对其优缺点进行点评,同时指出谨慎的化学前处理方法及质谱测定流程是获得高精度Rb同位素组成结果的基本前提;(2)收集了现有的地外样品Rb同位素组成数据,简述了Rb同位素在宇宙化学中的应用研究成果,指出Rb作为一个中度挥发性元素,对太阳系行星的吸积和演化过程具有重要的指示意义;(3)对Rb同位素在地质过程中潜在广阔的应用前景进行展望,例如完善经典的Rb-Sr定年体系,限定壳幔及地壳内部的分异过程,制约大陆硅酸盐岩风化,以及揭示超大型Rb矿的形成机制。

关键词: Rb稳定同位素, Rb化学分离, MC-ICP-MS, 宇宙化学过程, 潜在应用

Abstract:

Rubidium (Rb) is an alkali metal element with moderate volatility, fluid activity and high magmatic incompatibility, which is essential for tracing material provenance and providing valuable information on various geological processes. Meanwhile, 87Rb is a radioactive isotope which can decay to 87Sr with a long half-life (T1/2=4.976×1010 a). Therefore, Rb-Sr dating system has been widely used to determine geological age of long-time scale. Traditionally, Rb isotopic composition (87Rb/85Rb) of geological samples are considered constant for specific geological period. However, with advances in both Rb purification technique and Rb isotopic measurement by mass spectrometry, high-precision Rb isotopic compositions can be precisely determined. And the limited data show that geological samples can have different 87Rb/85Rb ratios due to isotopic fractionation during diverse geological processes. Questions still remain that whether Rb isotopic fractionation can provide additional clues for Rb tracing or affect precision of classical Rb-Sr dating method. To answer these questions, it is important to investigate δ 87Rb values of major geological reservoirs, discover Rb isotopic fractionation during various geological processes and explore the relevant mechanism of the fractionation systematically. Research in these areas, however, is extremely scarce to date. In this paper, we reviewed Rb isotope studies in the past 20 years, including analytical methods and fractionation mechanism, and provide our perspectives on relevant applications in the near future. The scope of our work and main findings are as follows: (1) We summarized previous studies regarding Rb chemical purification and instrumental measurement and compared the advantages and disadvantages of these techniques to show that careful chemical pretreatment and robust instrumental determination are the prerequisites for obtaining high-precision Rb isotopic ratios; (2) We compiled data on Rb isotopic compositions of extraterrestrial samples and briefly described Rb isotope application in cosmochemistry, e.g., as a moderate volatile element, Rb isotopes are promising in constraining accretion and evolution of the inner solar system; (3) Rb isotopes show potentials in solving many geological issues, such as improving classical Rb-Sr dating system, understanding differentiation process between crust and mantle, restricting continental chemical weathering processes, and advancing our understanding of Rb deposit formation.

Key words: Rb stable isotope, Rb chemical separation, MC-ICP-MS, cosmochemical process, promising application

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