微钻取样-TIMS/MC-ICPMS和LA-MC-ICPMS分析矿物岩石<sup>87</sup>Sr/<sup>86</sup>Sr比值的技术比较

张乐; 任钟元; 丁相礼; 吴亚东; 赖永旺

微钻取样-TIMS/MC-ICPMS和LA-MC-ICPMS分析矿物岩石⁸⁷Sr/⁸⁶Sr比值的技术比较

张乐^1,2,,
任钟元^1, ,,
丁相礼^1,2,
吴亚东^1,2,
赖永旺^1,2

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

基金项目:

国家自然科学基金重大研究计划项目（91214202）

详细信息

作者简介:
张乐，硕士研究生，同位素地球化学。E-mail: zhangle-001@qq.com

通讯作者:
任钟元，研究员，主要从事火成岩岩石学和同位素原位分析研究。E-mail: zyren@gig.ac.cn

中图分类号: O614.232;O657.63
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出版历程
- 收稿日期: 2014-04-08
- 修回日期: 2014-05-29
- 录用日期: 2014-05-29
- 发布日期: 2014-05-24

A Comparison of Microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS for Micro-sample Sr Isotope Measurement

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

摘要

摘要: 微区Sr同位素体系相对于传统全岩Sr同位素研究，可以揭示样品自身存在的不均一性，更好地反映样品经历的地质过程，已被广泛应用于各种地质研究领域，如研究壳幔相互作用、岩浆起源和演化，岩浆体系开放性研究，沉积盆地物源示踪及气候环境研究。准确测定Rb-Sr同位素比值是应用该同位素体系的前提。微钻取样-热电离质谱/多接收电感耦合等离子体质谱（TIMS/MC-ICPMS）和激光剥蚀多接收电感耦合等离子体质谱（LA-MC-ICPMS）作为分析地质样品微区Sr同位素组成的有效手段，已经得到了较为广泛的应用。两种技术在样品制备、干扰校正和质谱测试等方面各具优势和不足。微钻取样-TIMS/MC-ICPMS的最大优势是可获得高精度的Sr同位素数据（外精度优于100×10^-6，2SD）；但由于需要进行化学处理，流程繁琐耗时（约10天），实验周期较长，同时需要严格控制化学流程空白，且取样直径（200~2000 μm）和取样深度（100~2000 μm）较大，空间分辨率较低，但是该方法可以对高Rb样品（如钾长石）进行有效分析。LA-MC-ICPMS的最大优势是样品制备简单，数小时即可完成，且分析效率高，根据样品Sr含量的大小激光束斑直径多在60~300 μm之间变化，其空间分辨率较前一种方法高，可在短时间内对大量样品进行分析。但由于不能进行化学分离，分析过程中存在多种干扰（如Rb、Ca、Kr和REEs等），影响了测试的精度（约200×10^-6，2SD）和准确度（约150×10^-6）。该方法目前只能对高Sr低Rb的样品（如斜长石、磷灰石等）进行有效分析，而对于干扰元素含量较高的样品目前无法应用。本文认为，对于微钻取样法，应将改进化学流程作为重点研究方向，提高化学处理效率，同时改善微钻取样法的取样技术，减小取样直径和深度以提高空间分辨率；对于激光剥蚀法，重点突破Kr、Rb和二价REEs等干扰校正问题，提高干扰元素含量较高的样品的分析精度和准确度，同时需要提高仪器灵敏度以满足低Sr含量样品的分析要求。
- 锶同位素 /
- 微区分析 /
- 微钻 /
- 热电离质谱/多接收电感耦合等离子体质谱 /
- 激光剥蚀多接收电感耦合等离子体质谱
Abstract: Compared to the traditional strontium isotope analytical method, a micro-sample strontium isotope system study can reveal the heterogeneity of analyzed samples and is widely used in various fields of geology, such as crust-mantle interaction, genesis and evolution of magmas, open magma systems, tracing provenance of sedimentary basin and climate research. Accurate measurement of Rb-Sr isotopic ratios is the premise to apply Sr isotope in these research fields. Two detailed and widely used analysis methods for micro-sample Sr isotope measurement are microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS. These two methods have different advantages and disadvantages in sample preparation, interference correction and measurement in mass spectrometry. The greatest advantage of microdrilling-TIMS/MC-ICPMS is that this technique can acquire high quality data (external precision is better than 100×10^-6, 2SD). However the tedious chemical separation is very time-consuming (about 10 days) and the chemical procedure blank must be critical to low level. The large sampling depth (100-2000 μm) and diameter (200-2000 μm) reduce the spatial resolution. However, with chemical separation this method can effectively measure samples with high Rb content. Simple sample preparation and fast analysis are the most outstanding advantages of LA-MC-ICPMS which can analyze lots of samples in a much shorter time than that of microdrilling-TIMS/MC-ICPMS. The laser spot size is mainly from 60 to 300 μm. Based on Sr contents in samples, the method of LA-MC-ICPMS improved spatial resolution, compared to microdrilling-TIMS/MC-ICPMS technique. However, without chemical separation, many kinds of interferences (e.g. Rb, Ca, Kr and REEs) hinder this technique to obtain high quality data (external precision is about 200×10^-6, 2SD and accuracy is about 150×10^-6). LA-MC-ICPMS is only suitable for high Sr and low Rb samples, instead of samples with high content of interferences. Further studies are required for the microdrilling-TIMS/MC-ICPMS method to improve the efficiency of chemical separation, also microdrilling technology with increasing of spatial resolution by reducing spot diameter and depth. Meanwhile, a better solution for interferences of Kr, Rb and REEs is needed for LA-MC-ICPMS in order to improve precision and accuracy of high interference samples. Instrumental sensitivity improvement is also needed to satisfy Sr isotope measurement for samples with relative low Sr content.

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图 1 地幔和地壳中Sr同位素的演化(据Faure和Powell^[2])

Figure 1. The evolution of Sr isotope in mantle and crust (after Faure and Powell^[2])

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图 2 Sr同位素化学分离流程(据参考文献[26])

Figure 2. Sketch map of chemical separation for Sr isotope (after Reference [26])

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图 3 Rb和Sr淋洗曲线示意图(转自参考文献[26]，图 3)

Figure 3. Schematic diagram of elution of Rb and Sr (from Reference [26], Fig.3)

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图 4 钾长石Rb-Sr等时线(转自参考文献[7]的图 6)

Figure 4. Rb-Sr isochron diagram of a single K-feldspar crystal (from Reference [7], Fig.6)

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图 5 Columbia River玄武岩中的斜长石斑晶和基质的Sr同位素组成(修改自参考文献[50]的图 2)

Figure 5. The Sr isotopic composition of a plagioclase crystal and its host groundmass in Columbia River basalt (modified from Reference [50], Fig.2)

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表 1 两种微区⁸⁷Sr/⁸⁶Sr同位素分析方法对比

Table 1 A comparison of two methods for in-situ Sr isotope measurement

分析技术	化学处理	样品准备	质谱测试/样品 (单点)	采用直径 (μm)	采样深度 (μm)	Sr含量	Rb/Sr	精度 (2SD)	准确度	参考文献
微钻取样-TIMS /MC-ICPMS	是	约10天	1 h(TIMS)/ 10 min ^[18]	200~2000	100~ 2000	> 50×10 ^-6	不受限	< 50×10 ^-6 ~100×10 ^-6	< 50×10 ^-6	[5, 15, 26, 29]
LA-MC-ICPMS	否	几小时	3 min	60~300	50~200	> 300×10 ^-6	< 0.02	50×10 ^-6 ~250×10 ^-6	50×10 ^-6 ~250×10 ^-6	[16, 25, 38, 39, 40, 43]

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微钻取样-TIMS/MC-ICPMS和LA-MC-ICPMS分析矿物岩石87Sr/86Sr比值的技术比较

作者简介: 张乐，硕士研究生，同位素地球化学。E-mail: zhangle-001@qq.com

通讯作者: 任钟元，研究员，主要从事火成岩岩石学和同位素原位分析研究。E-mail: zyren@gig.ac.cn

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A Comparison of Microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS for Micro-sample Sr Isotope Measurement

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目录

微钻取样-TIMS/MC-ICPMS和LA-MC-ICPMS分析矿物岩石⁸⁷Sr/⁸⁶Sr比值的技术比较

作者简介:
张乐，硕士研究生，同位素地球化学。E-mail: zhangle-001@qq.com

通讯作者:
任钟元，研究员，主要从事火成岩岩石学和同位素原位分析研究。E-mail: zyren@gig.ac.cn