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单个熔体包裹体激光剥蚀电感耦合等离子体质谱分析及地质学应用

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometric Analysis Methods of Melt Inclusions and Its Geological Applications

  • 摘要: 熔体包裹体可以保留岩浆被捕获时的温度、压力及化学组成等信息,为研究岩浆结晶演化过程提供最直接有效的手段;然而由于取样方法、仪器分辨率和灵敏度等技术手段的限制,熔体包裹体研究(尤其是熔体包裹体成分研究方面)发展相对缓慢。本文在简述熔体包裹体特征与分类的基础上,总结了目前熔体包裹体成分研究的主要技术手段,包括技术特点、适用范围及样品制备等;详细介绍单个熔体包裹体激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)原位分析技术(原理、优缺点、定量方法等),并重点阐述分析过程中可能产生的元素分馏、基体效应及激光剥蚀技术要点等。单个熔体包裹体LA-ICP-MS原位分析技术的发展和完善,避免了传统熔体包裹体成分分析技术需加热均一化、样品制备繁琐等缺点,可直接对成分复杂矿物表面100 μm以下以多相形式存在的熔体包裹体进行整体分析,数据精确度可与电子探针分析和二次离子质谱相媲美,增加了样品中可分析熔体包裹体数量,更全面地反映岩浆演化信息,省时、高效、准确,极大地推动了熔体包裹体研究的发展。近年来,国内外单个熔体包裹体LA-ICP-MS原位分析技术应用于地质学和矿床学领域,在地球深部岩浆过程及岩浆热液矿床成矿理论等方面取得了重要成果。随着激光、质谱等设备的发展及定量方法完善,单个熔体包裹体LA-ICP-MS分析的准确性将进一步提高,同时单个熔体包裹体同位素原位分析技术的发展和应用将再次为熔体包裹体研究带来革命性进展。

     

    Abstract: Melt inclusions in phenocrysts play a very important role in petrological research for reserving the only direct information available on the temperature, pressure and chemical compositions of the magmatic system at the time that the host minerals crystallized. However, due to the limitation of techniques on sampling method, the resolution and sensitivity of the instrument, the study of melt inclusions (especially the chemical composition) is a relatively slow process. The melt inclusions properties and classifications generally are introduced in this paper, along with a summary of the analytical methods, applications and sample preparation, and an extensive description of the technique of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), especially the elemental fraction, matrix effects and principal points for laser ablation. The development of an in-situ micro-analytical technique by LA-ICP-MS, which can analyse the multi-phase inclusions up to 100 μm beneath the surface of the complex minerals, and avoids the prerequisite conditions of heating homogenization and sample preparation for the routine method is described. With the advantages of rapidity, efficiency and accuracy, the newly developed technique allows more analysis for melt inclusions in the same sample and comprehensively provides evolvement information for magma. Data accuracy can be comparable with Electron Microprobe Analysis and Secondary Ion Mass Spectrometry. Recently, this technique has been applied widely in research fields of geology and ore deposit geology. Furthermore, the significant achievements were obtained in the deep earth magmatic processes and magmatic hydrothermal metallogenic theory. The development of the equipment and quantitative methods will improve the accuracy of this technique. Meanwhile, the development and application of in-situ isotopic analysis of melt inclusions by LA-MC-ICP-MS will revolutionize melt inclusions research.

     

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