激光拉曼光谱仪定量测定硅酸盐熔体包裹体中水含量及其地质应用

Geological Application of Raman Spectroscopy to Quantify Trace Water Concentrations in Silicate Glasses

水作为深熔熔体中最常见的一种挥发分,是影响熔体的物理和化学性质的主要因素.由于现有的测试技术以及熔体包裹体自身的局限性,很难定量确定熔体包裹体中水的含量和种型,导致对俯冲带熔体产生机制和演化过程的认识也极为有限.共聚焦显微激光拉曼光谱仪具有高的空间分辨率、快速、无损分析、样品制备简单等优点,且可分析暴露于表面或包裹于内部的样品,因此对探测微小熔体包裹体具有极大的优势.该方法的原理是基于拉曼谱峰高度/强度与其对应基团含量具有良好的线性关系,以人工合成硅酸盐玻璃为标准样品,用于硅酸盐熔体包裹体中水的含量和种型的定量限定.作为新发展起来的技术和方法,越来越多地引起地质学家的关注,但是目前大量的研究还集中于该分析方法自身的推演和校正,对天然样品的研究还相对缺乏.目前有限的研究表明,该方法可被广泛应用于岩浆岩和高级变质岩体系中,不仅可定量限定岩浆岩基质或斑晶中硅酸盐熔体包裹体水含量,有效示踪岩浆侵入或喷发过程中岩浆的流变学行为;而且可定量限定俯冲带内经历过部分熔融的高级变质岩中代表初始熔体的多晶矿物包裹体中水的含量和种型,示踪俯冲带熔体组成和演化,进而为研究深俯冲地壳分异、板片-地幔楔界面的熔体交代作用等重要问题提供新的制约.

Water,the primary volatile constituent in anatectic melt and terrestrial magma,has a significant effect on the physical and chemical properties of the melt.Due to limitations in analytical techniques and the fugitive nature of anatectic melts,it is extremely difficult to quantitatively determine water concentration and water speciation,resulting in a very limited understanding of the formation mechanism and evolution process for partial melting in subduction zone.Confocal micro-Raman spectroscopy,which has the advantages of high spatial resolution,fast,nondestructive analysis and simple sample preparation,severs the purpose of detecting small melt inclusions.Additionally,based on the principle that there is a good linear relationship between the height/intensity of Raman spectrum peak and the content of corresponding groups,the internal calibration and external calibration are established for the quantitative analysis of water content and water speciation in silicate melt inclusions with synthesized silicate glass as the standard sample.As a newly developed technique and method,more and more geologists pay attention to it.However,a large number of researches are still focused on the deduction and correction of the analytical method itself,while the research on natural samples is relatively lacking.Limited research indicates that the method can be widely used in magmatites and high-grade metamorphic rocks.It achieves quantitatively determining the water content of matrix or melt inclusion in porphyry,thereby effectively tracing the rheological behavior of magma during magma intrusion or eruption.Water content and speciation of the anatectic melt in the continental subduction zone provides tight constraints for continental crust differentiation and melt metasomatites at the slab-wedge interface.