名义上无水矿物(nominally anhydrous minerals,简称NAMs,如橄榄石、辉石、石榴石、长石等)中以缺陷形式存在的结构水的重要性已经被地球科学界广泛认同,并得到了越来越多的关注.由于对OH振动的高度敏感性,红外光谱方法被广泛用来测量NAMs中"水"的赋存状态、含量以及在晶体结构中的位置.随着傅立叶变换红外光谱仪的不断发展及分析技术的提高,以及红外附件的更新换代,出现了一些新的分析方法.原位变温红外光谱实验就是利用变温红外附件测量样品在不同温度下的红外光谱,通过研究不同温度下红外光谱图的峰形、峰位、峰数等参数的变化,了解温度改变过程中样品所发生的物理、化学变化,且具有实时监测的优点,因此广泛用于含水矿物和玻璃中OH和H2O的研究.主要包括含水矿物和玻璃的脱水机理及脱水动力学研究,OH和H2O的红外吸收系数的温度依赖性及不同温度下红外吸收系数的校正等方面.虽然原位变温红外光谱广泛应用于含水矿物和玻璃中水的研究,但是应用于名义上无水矿物还是刚刚起步.NAMs中的H是活动的,高温下H的赋存状态及其在晶体中的位置可能会不同于室温,而地质过程往往都在高温下进行,研究高温下NAMs中的水具有重要的地质学意义.因此,有必要利用原位变温红外光谱实时监测不同温度下NAMs中水的变化.有关NAMs中水的原位变温红外光谱实验早期工作只是观察不同温度下谱图参数的变化并给予一定的解释,以及用此法来确定NAMs中水的赋存状态.受含水矿物和玻璃的研究结果的启发,原位变温红外光谱实验目前也开始用来研究NAMs中水的脱水机理和扩散动力学.此外,利用原位变温红外光谱技术,通过研究不同温度下OH的积分吸收面积可探索NAMs中OH红外吸收系数温度依赖性;通过研究OH峰位随温度移动的幅度与某些化学成分的关系,可给出NAMs中OH的结合机理方面的有用信息.虽然近些年来已经开展了一些工作,取得了一些新的成果,但是总的说来还处在起步阶段,今后针对NAMs的研究重点应该集中在以下三个方面:(1)吸收系数温度依赖性的定量化,(2)脱水机理和动力学的扩展,(3)OH结合机理研究的深入.%The knowledge of OH incorporated in nominally anhydrous minerals (NAMs) is crucial for understanding the chemical and physical properties of the Earth's interior. Infrared Spectrometry (IR) is a powerful tool to detect trace amount of water in NAMs because of its high sensitivity, so it is widely used in investigating the species, concentration and site in crystals of water in NAMs. With the improvement of instruments and analytical techniques, more accessories attached with Fourier Transform Infrared spectroscopy (FTIR) are applied. In situ FTIR analysis at varying temperatures can be used to obtain the spectra under different temperatures timely, so it is widely utilized in studying behavior of OH and H2O in hydrous minerals and glasses. Examining the variation of such spectra parameters as band position, band shape and band number with temperature can be used to study the dehydration mechanisms and diffusivity of hydrous minerals and glasses. Moreover, temperature dependence of IR absorption coefficient OH and H2O in glasses found by this technique call upon the correction of temperature-dependent absorption coefficients. Although in situ varying temperature FTIR technique is widely used in investigating OH and H2O in hydrous minerals and glasses, the application for NAMs is still scarce. The hydrous components in minerals are active and mobile, the speciation and sites of hydrous components under temperatures of geologic interest may be not the same as those at room temperature. So it is indispensable to obtain the spectra of water in NAMs under different temperatures timely. The earlier work using this technique for NAMs simply examined the change of the spectra with temperature and identified H species. Now, inspired by the relevant work of hydrous minerals and glasses, in situ varying temperature FTIR technique is also utilized in investigating dehydration mechanisms and diffusivity of water in NAMs. Moreover, using in situ varying temperature FTIR technique, temperature dependence of integral absorption coefficients of OH in NAMs can be studied through observation of IR integral absorbances of OH at different temperatures. On the other hand, by analyzing the relationship between chemical composition and altitude of the change of band frequency with temperature, the information about OH incorporation mechanism in NAMs can be explored using in situ varying temperature FTIR technique. Although some work has been carried out in recent years and has obtained some new achievements, the research about OH in NAMs using in situ varying temperature FTIR technique is still in preliminary stage. Further studies in NAMs by this technique will be focused on the followings: (1) quantifying the temperature-dependence of OH IR absorption coefficient; (2) expanding the study of dehydration mechanism and kinetics; (3) exploring the OH incorporation mechanism.
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