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王志海, 叶美芳, 董会, 赵慧博, 王轶. 流体包裹体盐度低温拉曼光谱测定方法研究[J]. 岩矿测试, 2014, 33(6): 813-821. DOI: 10.15898/j.cnki.11-2131/td.2014.06.009
引用本文: 王志海, 叶美芳, 董会, 赵慧博, 王轶. 流体包裹体盐度低温拉曼光谱测定方法研究[J]. 岩矿测试, 2014, 33(6): 813-821. DOI: 10.15898/j.cnki.11-2131/td.2014.06.009
Zhi-hai WANG, Mei-fang YE, Hui DONG, Hui-bo ZHAO, Yi WANG. Determining Salinity of Fluid Inclusions by Cryogenic Raman Spectroscopy[J]. Rock and Mineral Analysis, 2014, 33(6): 813-821. DOI: 10.15898/j.cnki.11-2131/td.2014.06.009
Citation: Zhi-hai WANG, Mei-fang YE, Hui DONG, Hui-bo ZHAO, Yi WANG. Determining Salinity of Fluid Inclusions by Cryogenic Raman Spectroscopy[J]. Rock and Mineral Analysis, 2014, 33(6): 813-821. DOI: 10.15898/j.cnki.11-2131/td.2014.06.009

流体包裹体盐度低温拉曼光谱测定方法研究

Determining Salinity of Fluid Inclusions by Cryogenic Raman Spectroscopy

  • 摘要: 氯盐溶液作为流体包裹体中最普遍和最重要的盐水化合物, 是测定包裹体盐水溶液含盐度的主要溶质, 但由于其强离子键化合物的分子特性在常温、常压下没有拉曼效应, 拉曼光谱测试无法获取氯盐的有效特征信息, 使得利用拉曼光谱研究流体包裹体分子组分及含盐度的方法存在严重缺陷。本文联合利用激光拉曼光谱探针和冷热台, 原位采集了不同盐度的NaCl-H2O和CaCl2-H2O标准盐水溶液在低温下(-185℃)形成的冰、NaCl水合物和CaCl2水合物的拉曼光谱, 分析了不同盐度标准盐水溶液形成的水合物拉曼特征峰的变化规律, 尝试建立流体包裹体盐度低温拉曼光谱测定方法。分析表明, NaCl水合物约3425 cm-1拉曼特征峰与冰约3120 cm-1拉曼特征峰峰面积比值和配制的NaCl-H2O标准溶液盐度呈良好的正相关(r2=0.9995), CaCl2水合物约3431 cm-1拉曼特征峰与冰约3120 cm-1拉曼特征峰峰面积比值也和配制的CaCl2-H2O标准溶液盐度呈较好的正相关(r2=0.9458)。利用愈合人工水晶法合成的NaCl-H2O和CaCl2-H2O包裹体标样检验了用上述方法低温测定流体包裹体盐度的可靠性, 结果表明该技术用于盐度大于0.5 mol/L的NaCl-H2O体系流体包裹体时, 数据精度好于20%;用于盐度大于0.5 mol/L的CaCl2-H2O体系流体包裹体时, 数据精度最高可达5%, 完全可达到半定量-定量测定的要求。研究还发现, 包裹体内压可能对低温拉曼光谱测定流体包裹体盐度影响不大, 分析中获得的冰拉曼特征峰的拉曼位移(约3120 cm-1)与前人略有差异, 可能与实验条件下获得的冰的多型不同有关。与国内外同行的研究结果比较, 本研究更加注重该项实验技术的实际应用, 通过对不同体系盐水溶液系列进行拉曼光谱实验分析, 对实验条件和方法进行不断优化, 在确定流体体系的同时实现了包裹体盐水溶液盐度半定量-定量测定, 准确度优于传统方法, 并且该方法具有很强的实用性。

     

    Abstract: Chlorides are the most common and important solutes in liquid phase of natural fluid inclusions, but they are difficult to study by Laser Raman Microscopy (LRM) at room temperature, due to their strong ionic bonds, which are not Raman active under experimental conditions. This problem seriously hinders the utilizing of LRM in a fluid inclusion study, neither for their specific components in both vapor and liquid phases, nor for their salinity. In combination with laser Raman Spectrometry and hot and cold operation boards, Raman spectra of ice, sodium chloride hydrate and calcium chloride hydrate, which were formed by frozen NaCl-H2O and CaCl2-H2O solutions with different concentrations at low temperature (-185℃) were acquired. According to systematic analysis and comparison of Raman spectra of sodium and calcium chloride hydrates with different concentrations, an attempt was made to establish a method for salinity determination by cryogenic laser Raman Spectroscopy. Results show that the area ratios of Raman bands at about 3425 cm-1 of sodium chloride hydrates to which at about 3120 cm-1 of ice were in good correlation with prepared concentrations of NaCl-H2O solutions (r2=0.9995). Similarly, area ratios of Raman bands at about 3431 cm-1 of calcium chloride hydrates to that at about 3120 cm-1 of ice were in good correlation with prepared concentrations of CaCl2-H2O solutions, too (r2=0.9458). Reliability of this method was examined by synthetic NaCl-H2O and CaCl2-H2O inclusions, which were prepared by healing microfracture of quartz crystals under high pressure and temperature conditions when the crystals were dipped in solution of specific concentration. Inspection results show that when this method is applied to > 0.5 mol/L NaCl-H2O fluid inclusions, the accuracy is better than 20%. Meanwhile, when applied to > 0.5 mol/L CaCl2-H2O fluid inclusions, the best accuracy might reach to 5%. The results meet semi-quantitative to quantitative analysis requirements for fluid inclusions. The interior pressure of fluid inclusions might be less important in salinity determination of fluid inclusions by cryogenic Raman Spectroscopy. The Raman bands of ice were somewhat different to those acquired by most other researchers (at about 3120 cm-1 in this study), which is most likely due to different polymorphs formed under the experimental condition. This method allows knowledge of the main fluid system to be attained as well as the salinity of fluid inclusions semi-quantitatively to quantitatively, with improved accuracy over traditional techniques.

     

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