Distributions and properties of grain boundary thin film water in the earth's interior

为了研究地球内部水的分布和性质，利用红外显微光谱方法对各种地壳和地幔物质中的水进行了测量。1)近场红外显微光谱结合近场显微光谱技术，提出了一种新的水的表征方法。这和红外近场红外（NFIR）显微光谱可以测量水的化学状态和含量，在约300nm的亚微米尺度下可测量约1%。该方法对微晶石英聚集体（玛瑙）的成像结果显示，水沿晶界的约束结构具有较短的氢键距离。2)地壳和地幔物质中水的分布对各种地壳和地幔岩石进行红外显微光谱分析，揭示了地球内部水的分布规律。a)近200 km深俯冲变质岩中的水分布在斜长岩和斜长岩的缺陷中，其中石榴石较多，平均含量为2000 ppm，表明水向地幔输送。b)地幔中的水可以储存在钙钛矿等地幔矿物的缺陷中，最高可达2000ppm左右。这相当于现在地幔中可储存的海水的5倍。c)利用我们研究确定的摩尔吸收系数，可以用红外显微光谱测量岩浆和喷发物质中的水分。该技术还可用于研究岩浆的原位脱水行为。d)变质岩剪切带中的流体由于其化学性质（NaCl vs. co2）而具有不同的润湿性质，并且在变质条件下，这种润湿性质的差异预计会大得多。e)发现低品位变质岩中的水主要分布在粒界内。3)合成晶界水和合成水溶液为了实验研究晶界水的结构和性质，采用红外显微光谱法对几种合成薄膜水进行了测量。薄膜水的OH拉伸吸收峰从3400 cm-1左右移动到3200cm-1左右，表明靠近冰的氢键距离较短。夹在矿物中的水似乎被限制在200纳米左右。这种结构改变取决于矿物种类和晶体取向。用ATR红外光谱对合成水溶液进行了研究，NaCl溶液表现出较松散的性质，氢键较长，碳酸盐溶液表现出较紧密的性质，氢键较短。这些水溶液在更高的温度下变得“更松散”。我们于2003年9月13日在东京工业大学组织了一次国际研讨会，与来自物理、化学和地球科学的国际专家讨论这些结果。研讨会的结果现在被编辑成一本论文集，将于2004年7 - 8月出版（Nakashima， S.Mercury）。L.Fenter， P.和Spiers， C.J.(2004)，“水的物理化学和材料与地球的动力学——薄膜水的结构和行为”，环球科学院出版社。东京，约200便士。)少

In order to study the distributions and properties of water in the earth's interior, infrared microspectroscopic methods have been used to measure water in various crustal and mantle materials1)Near-Field infrared MicrospectroscopyA new water characterization method has been developed by combining a near field microscopy spectroscopy. This and infrared Near-field infrared (NFIR) microspectroscopy can measure chemical states and contents of water down to about I wt% in submicron scale down to about 300nm. Mapping results by this NFIR method on microcrystalline quartz aggregates (agate) revealed constrained structures of water along grain boundaries with shorter hydrogen-bond distances.2)Distribution of water in the crust and mantle materialsinfrared microspectroscopy on various crustal and mantle rocks revealed the following distributions of water in the earth's interior.a)Water in deep subducted metamorphic rock to the depth of about 200 km is distributed in defects in clinopyroxnes ar … More id garnets with average contents of 2000 ppm, evidencing the water transport to the mantle.b)Water in mantle can be stored in defects of mantle minerals such as perovskites upto about 2000 ppm. This is corresponding to 5 times as much water as the present sea water can be stored in the mantle.c)Water in magma and erupted materials can be measured by infared microspectroscpy by using molar absorption coefficients determined by our studies. In-situ dehydration behaviors of magma can be studied also by this technique.d)Fluids in shear zones in metamorphic rocks have contrasted wetting properties due to their chemistries (NaCl vs. C02) and this difference in wetting properties is expected to be much larger at metamorphic conditions.e)Water in low grade metamorphic rocks is found to be distributed mainly ingrain boundaries.3)Synthetic grain boundary water and synthetic aqueous solutionsIn order to study experimentally the structures and properties of water in grain boundaries, several synthetic thin film water have been measured by infrared microspectroscopy. Thin film water showed a OH stretching absorption peak shift from 3400 to around 3200cm-1 indicating shorter hydrogen-bonding distance close to ice. Water sandwitched in minerals appeared to be constrained from about 200nm. This structural modification is dependent on mineral species and crystallographic orientations.Synthetic aqueous solutions were studied by Attenuated Total Reflection (ATR) infrared spectroscopy, and NaCl solutions showed more loose nature with longer H-bond, while carbonate solutions indicated more tight nature with shorter H-bond. These aqueous solutions become "looser"at higher temperatues.We organized an international symposium on September 13, 2003 in Tokyo Institute of Technology to discuss these results with international experts from physics, chemistry and earth sciences. The results of the symposium is now edited as a proceeding book which will be published in July-August 2004 (Nakashima, S.Mercury. L.Fenter, P. and Spiers, C.J.(2004)"Physicochemistry of Water and Dynamics_of Materials and the Earth-Structures and behaviors of the thin film water-"Universal Academy Press. Tokyo,〜200p.) Less