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，人们利用红外显微光谱方法对各种壳幔物质中的水进行了测量。1）近场红外显微光谱（Near-Field Infrared Microscopicology）结合近场显微光谱（Near-Field Microscopicology），发展了一种新的水表征方法。这种和红外近场红外（NFIR）显微光谱可以在低至约300 nm的亚微米尺度下测量低至约1重量%的水的化学状态和含量。利用该方法对微晶石英集合体（玛瑙）的成像结果揭示了水沿着晶界的束缚结构，氢键距离较短。2）水在地壳和地幔物质中的分布对各种地壳和地幔岩石的红外显微光谱分析揭示了以下水在地球内部的分布：a）深俯冲变质岩石中的水分布在单斜辉石中的缺陷中，深度约为200 km 关于我们 d石榴石，平均含量为2000 ppm，证明地幔中存在水的输送.B）地幔中的水可储存在地幔矿物如钙钛矿的缺陷中，含量可达2000 ppm左右.这相当于现今地幔中所能储存的海水的5倍。c）岩浆和喷发物中的水可以用红外显微光谱法测量，用我们的研究确定的摩尔吸收系数。该技术还可用于研究岩浆的原位脱水行为。d）变质岩石剪切带中的流体由于其化学性质而具有不同的润湿性（NaCl vs.C02），在变质条件下，这种润湿性的差异预计要大得多。e）发现浅变质岩石中的水主要分布在内部边界。3）合成晶界水和合成水溶液为了从实验上研究晶界水的结构和性质，我们用显微红外光谱法测量了几种合成薄膜水。薄膜水的OH伸缩吸收峰从3400 cm ~（-1）移动到3200 cm ~（-1）附近，表明在冰附近氢键距离较短。水在矿物中的夹层似乎被限制在200 nm左右。合成水溶液的衰减全反射（ATR）红外光谱研究表明，NaCl溶液中氢键较长，结构较松散，而碳酸盐溶液中氢键较短，结构较紧密。2003年9月13日，在东京工业大学举办了国际研讨会，与来自物理、化学、地球科学等领域的国际专家就这些结果进行了讨论。研讨会的结果现在被编辑成一本会议录，将于2004年7月至8月出版（Nakashima，S.Mercury. L.Fenter，P.和Spiers，C.J.（2004）“水的物理化学和动力学_材料和地球-薄膜水的结构和行为-”环球学院出版社。东京，200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