【作者】 杨燕；

【导师】 夏群科；

【作者基本信息】 中国科学技术大学 ， 地球化学， 2011， 博士

【摘要】 名义上无水矿物（nominally anhydrous minerals,简为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学界广泛认同,并得到了越来越多的关注。NAMs中的H是活动的,H在高温下的赋存状态、物理化学性质以及在晶体结构中的位置都可能不同于室温,基于NAMs的重要性以及地质上更感兴趣的温度是高温,因此很有必要分析变温下NAMs中的H。由于红外对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,因而原位变温红外光谱技术是监测不同温度下NAMs中H的一种很好的方法。但是,目前仅有少数工作涉及到矿物和玻璃中“水”的红外吸收温度依赖性的研究,更没有人对天然的NAMs中OH变温红外光谱做系统的研究。本文以单斜辉石、斜方辉石、长石以及金红石等天然名义上无水矿物为例,常温下利用傅立叶变换红外光谱技术检测样品中结构水的存在与否及其赋存形式;对结构水含量相对较高的样品进行电子探针化学成分分析;利用配接在红外显微镜上的冷热台及温控装置进行原位变温红外光谱分析（从室温间隔100℃升高到500℃）;对典型样品进行不同角度的偏振分析。以研究OH的红外吸收温度依赖性和结合机理为出发点,详细观察矿物中同一分析区域在不同温度下谱图的变化,循序渐进地做了以下工作:（1）运用显微傅立叶变换红外光谱（Micro-FTIR）技术观察了单斜辉石（普通辉石）和斜方辉石（顽火辉石）中结构OH在原位连续加热、降温和阶段加热过程中的变化,从而更清楚地了解了缺陷氢在晶体结构中的位置及其结合机制。温度从室温升到500℃,间隔100℃。结果表明,单斜辉石和斜方辉石的红外谱图随温度变化的趋势相同,即:OH的伸缩振动峰位都是随温度升高而向低波数移动,而且这种变化是可逆的。峰位的移动主要受H所取代的阳离子位置或晶格空隙热膨胀的影响。（2）受辉石变温红外光谱的初步实验结果启发,以单斜辉石（包括普通辉石、透辉石和绿辉石）为研究对象,结合变温红外及偏振红外实验,依据晶体化学理论及键长与振动频率的关系,从一个新的角度--热膨胀速率,探讨了单斜辉石中缺陷OH的结合机理。结果表明:单斜辉石中OH的红外吸收峰主要有三组:（1） 3600-3620 cm^-1;（2） 3500-3540 cm^-1;（3） 3445-3465 cm^-1。第1组峰对应的OH结合方式是Si⁴⁺+O²-+1/2 H₂-Al³⁺+OH^-;而第3组峰对应的OH结合方式是H填充M2空位。第2组峰对应的OH结合方式复杂,可能和多个位置有关。第2和第3两组OH偶极的振动方向一致,都是M1和M2的共棱O2-O1,而第1组OH偶极的振动方向则是M2的O2-O3棱。（3）为了更详细地研究单斜辉石的3组吸收峰(3600-3620 cm^-1;3500-3540 cm^-1;3445-3465 cm^-1)对温度的依赖性,选择普通辉石和透辉石的主要吸收峰来研究第1组峰,选择绿辉石的主要吸收峰来研究第2和3组吸收峰。对这些样品进行原位变温红外光谱实验,分析这三组峰的峰位随温度变化的结果,发现第1组吸收峰的峰位随着温度升高向低波数移动,第2和3组吸收峰也向低波数移动,但是移动幅度相对很小。透辉石的第1组OH峰虽然都在3600-3620 cm^-1之间,但是不同样品的起始峰位不同,通过不同透辉石样品变温实验的对比发现:不同的起始峰位随温度变化的幅度不同,起始峰位越高,随温度变化的幅度越大。普通辉石和绿辉石结构OH的总积分吸收面积均随着温度的升高而减小。从500℃降到室温时它们的红外光谱变化可逆,说明实验过程中没有发生OH损失等不可逆过程,所以积分吸收面积的变化反映了OH吸收系数的变化,因此,在利用Beer-Lambert定律计算辉石OH含量时,一定要注意吸收系数的选择。（4）将变温红外实验的样品扩展到斜方辉石和长石,分析影响吸收系数变化的因素。结果显示,不仅峰位随温度移动的幅度与起始峰位有关,峰位随温度移动方向也与起始峰位有关。这些矿物中OH的吸收系数均随着温度的升高而减小,但是减小的幅度不同。结合单斜辉石和石榴石的实验结果发现,这些NAMs中的OH吸收系数随温度变化的幅度与峰位有关:OH平均峰位越低的矿物,OH吸收系数受温度影响越大,反之OH平均峰位越高的矿物,OH吸收系数受温度影响越小。（5）针对前人工作和本文前面章节所涉及到的工作的局限性,即:没有从晶体化学和晶体结构的角度对不同温度下光谱的变化做出解释,我们选择一种简单矿物――金红石,对其除了进行原位高温红外实验,还增加了原位低温红外和偏振红外实验,以及变温X射线衍射实验,从而深入探讨H在不同温度下的变化。结合这些实验结果,分析得出以下结论:金红石中的两组OH峰对应的H位在晶体结构中的（001）面,常温下,3297 cm^-1峰的H在（1/2,0,0）位,3279 cm^-1峰对应的H在（1/2,1/2,0）位,并且形成弯曲的氢键。温度变化时,两个峰的吸收面积变化方向相反,说明两种可能性:（1）H会发生位置迁移,以维持晶体结构的稳定性,高温时H主要位于（1/2,1/2,0）,低温时H主要位于（1/2,0,0）位;（2）两组峰的吸收系数有着相反的温度依赖性。更多还原

【Abstract】 The knowledge of OH incorporated in nominally anhydrous minerals （NAMs） is crucial for understanding the chemical and physical properties of the Earth’s interior. The H in NAMs is mobile and the speciation, physicochemical properties and sites in the crystal structures may vary with temperature. So it is indispensable to analyze H in NAMs at different temperatures. IR is a powerful tool to detect trace amount of OH in NAMs because of its high sensitivity, so, it is widely used to measure water content in NAMs and explore H incorporation mechanism. Thereby, in situ varying temperature FTIR technique is a very good method to detect H in NAMs at different temperatures. Although some researchers have investigated temperature dependence of OH and H2O absorption in some minerals and glasses, the study concerning possible behavior of OH absorption in natural NAMs at varying temperatures is still scarce. In this dissertation, we choose such common minerals as clinopyroxene, orthopyroxene, feldspar and rutile to identify H speciation using Micro-FTIR method at room temperature. Then chemical compositions are analyzed by use of EMPA for minerals with high water content. At last, in situ FTIR experiment is carried out to investigate the variation at varying temperatures （from RT to 500℃at 100℃increments） using heating/cooling stage attached to IR microscope. Moreover, polarized IR measurement is carried out for typical samples. In order to investigate the temperature dependence of IR absorption coefficient and incorporation mechanism of OH in NAMs, the followings are completed step by step:（1） The behavior of structural OH in clinopyroxene （cpx） and orthopyroxene （opx） during successive heating, cooling and stepped heating has been investigated by in situ Micro-FTIR measurements under temperatures ranging from 25℃to 500℃at 100℃increment. The results suggest that both Cpx and Opx exhibit a decrease in OH stretching vibration frequency with increasing temperature, and the change is reversible. Shift in absorption band frequency is controlled by thermal expansivity of the OH site or lattice interstice.（2） Based on the FTIR experiment results at varying temperatures for diopsides and omphacites, we discussed the incorporation mechanisms of OH defects in clinopyroxene mineral from a new point of view ---- thermal expansion. There are three groups of OH absorption bands in clinopyroxene: （1） 3600-3620 cm^-1; （2） 3500-3540 cm^-1; and （3） 3445-3465 cm^-1. The OH incorporation mode of group 1 band is Si⁴⁺+O²-+1/2 H₂-Al³⁺+OH^-, while the M2 vacancy is responsible for the OH incorporation mode of group 3 band. The OH incorporation mode of group 2 band is complex and probably relates to several different positions. The OH dipole vibration direction of group 2 band is the same with group 3 bands, along shared edge of M1 and M2 polyhedra O2-O1. And the OH dipole of group 1 band vibrates between O2 and O3 along edge of M2 polyhedron.（3） The behavior of structural OH in clinopyroxene （augite and omphacite） during successive heating has been investigated by in situ Micro-FTIR measurements under temperatures ranging from room temperature to 500℃at 100℃increment. The first group of OH band (3620-3640 cm^-1) exhibits a systematic decrease of peak position upon successive heating, while the other two groups (3520-3535 cm^-1, 3450-3465 cm^-1) show only little change. Both augite and omphacite display a decrease of integral absorbance of OH fundamental stretching vibration upon successive heating. The IR spectra of OH band are reversible when the temperature decreases from 500℃to room temperature, suggesting that changes in IR indicate changes in molecular state of OH and no loss of OH happens. The change of integral absorbance of OH bands indicates that OH absorption coefficient is temperature dependent, so it is necessary to apply different absorption coefficients when determining OH content from Beer-Lambert law at different temperatures and sample temperatures should be reported in quantitative IR studies.（4） Temperature dependence of IR absorption of OH in nominally anhydrous orthopyroxene and feldspar has been investigated by in situ Micro-FTIR measurements under varying temperatures ranging from 25℃to 500℃at 100℃increment. The results demonstrate that the shift direction of OH peak position is related with initial wavenumber. Integral absorbances of OH in orthopyroxene and feldspar decrease with increasing temperature. Although the trend is similar to that of clinopyroxene, the magnitude of temperature response of OH integral absorbances of these minerals is variable. The magnitude of temperature responses are correlated with wavenumbers: the lower wavenumber bands have stronger temperature dependence of integral absorbances. The changes of IR spectra of OH band are reversible, so the change of integral absorbance with temperature indicates temperature-dependent IR absorption coefficient of OH in nominally anhydrous minerals （NAMs）. （5） In view of the limitations of previous works and in order to deeply investigate the IR behavior of NAMs at different temperatures, we choose a very simple mineral-rutile, not only carry out in situ high temperature FTIR measurements, but also in situ low temperature FTIR, polarized FTIR and high temperature XRD. The combined results suggest that the H site of rutile is on the （001） plane. At room temperature, the H site of 3297 and 3279 cm^-1 band is on （1/2, 0, 0） and （1/2, 1/2, 0） respectively. In addition, the H bond of 3279 cm^-1 band is nonlinear. The change of areas for these bands shows opposite dependency on temperature, indicating two possibilities: （1） H site will transfer at varying temperatures and （1/2, 1/2, 0） site is stable at high temperature, while the other site （1/2, 0, 0） is stable at low temperature; or （2） the IR absorption coefficients of two bands display opposite temperature dependency.更多还原