名义上无水矿物的水含量及其地质应用

发布时间：2018-05-31 15:03

本文选题：名义上无水矿物 + 傅里叶变换红外光谱　；参考：《中国科学:地球科学》2016年05期

【摘要】：名义上无水矿物(NAMs)中能够保存微量的与晶体缺陷相关的结构水.这些水可以使用傅里叶变换红外光谱(FTIR)和二次离子质谱(SIMS)等分析方法进行测定.到目前为止,已有相当多的研究系统地报道了不同岩相中NAMs的水含量,特别是地幔橄榄岩包体.在橄榄岩包体中,水在橄榄石中的分布经常呈核部浓度高,边部浓度低的扩散曲线,这显示橄榄石中的水在包体随岩浆上升过程中发生了扩散丢失,而辉石中水的分布通常是均一的,并且一般认为辉石保留了地幔值.利用水在硅酸盐矿物-熔体间的分配系数可以计算与这些矿物平衡的岩浆的水含量.此方法可以进一步被用于估算母岩浆以及源区的水含量,但方法受制于适合于研究体系的分配系数的选取.利用地幔NAMs的氢同位素组成以及H_2O/Ce比值可以示踪上地幔中水的源区和地幔中水含量的不均一性.水对克拉通岩石圈地幔的稳定性有重大影响,但是不同克拉通岩石圈的水含量和垂向分布存在显著差异,这是由于不同的地质活动所导致,而地幔柱和克拉通的相互作用可能并不会导致克拉通岩石圈水含量的显著变化.由于地幔NAMs含水量数据的局限性,目前上地幔水含量的估算仍建立于地球化学模型的基础之上.
[Abstract]:Nominally anhydrous minerals (NAMs) can preserve trace amounts of structural water related to crystal defects. The water can be determined by Fourier transform infrared spectroscopy (FTIR) and secondary ion mass spectrometry (SIMS). Up to now, quite a lot of studies have systematically reported the water content of NAMs in different lithofacies, especially the mantle peridotite inclusion. In peridotite inclusions, the distribution of water in olivine tends to be a diffusion curve with high nuclear concentration and low marginal concentration, which indicates that the water in olivine is lost in the process of magma rising. The distribution of water in pyroxene is generally uniform, and it is generally believed that pyroxene retains the mantle value. Using the water partition coefficient between silicate minerals and melts, the water content of magma in equilibrium with these minerals can be calculated. This method can be further used to estimate the water content of the parent magma and the source area, but the method is limited by the selection of distribution coefficients suitable for the study system. The hydrogen isotopic composition of mantle NAMs and the H_2O/Ce ratio can be used to trace the source region of water in the upper mantle and the heterogeneity of water content in the mantle. Water has great influence on the stability of craton lithospheric mantle, but there are significant differences in water content and vertical distribution among different cratonic lithosphere, which is caused by different geological activities. However, the interaction between mantle plume and craton may not result in significant change of water content in craton lithosphere. Because of the limitation of NAMs water content data, the estimation of upper mantle water content is still based on geochemical model.
【作者单位】：南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室;
【基金】：国家自然科学基金项目(批准号:41590623,41573055) 中央高校基本科研业务费中组部青年千人计划项目资助
【分类号】：P574

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