CCSD超高压榴辉岩中的水:红外光谱分析

超高压变质岩中名义上无水矿物(NAMs) 在板块俯冲过程中可以携带一部分地表水进入上地幔, 这些水储存于地球深部并对地幔动力学有着重要的影响.对中国大陆科学钻探主孔榴辉岩中的绿辉石和石榴石进行了详细的显微傅立叶变换红外光谱(Micro-FTIR) 分析, 结果显示所有绿辉石和石榴石颗粒都含有结构水, 其水含量范围分别在68~29μg/g和20~75μg/g.榴辉岩全岩的水含量为150~300μg/g.绿辉石和石榴石结构水含量的分布出现2种情况: (1) 颗粒内部的均一分布; (2) 不均匀分布, 表现为水含量从核部到幔部到边部随之增加或水含量核部、边部低而幔部高.电子探针结果表明水含量分布不均与矿物化学成分无直接关系.位错分布不均匀可能导致了颗粒内部结构水分布的不均匀. 

Water in UHP Eclogites at CCSD: FTIR Analysis

Along with the processes of continent crust subduction, the nominally anhydrous minerals (NAMs) in UHP rocks can transport some surface water into the deep upper mantle. Such water stored in the deep upper mantle plays an important role in the dynamics of the earth's interior. Omphacite and garnet in UHP eclogites from the Chinese Continental Scientific Drilling (CCSD) main hole have been investigated by Fourier transform infrared spectroscopy (FTIR) in this work. The result demonstrates that all omphacite and garnet grains contain structural water from 68μg/g to 529μg/g and from 20μg/g to 875μg/g respectively; the contents of structural water in the whole rock of eclogite range from 150μg/g to 300μg/g. There are two types of water distribution characteristics within single garnet and omphacite grains, one is homogeneous and the other is inhomogeneous. The inhomogeneous phenomena show that the water contents increase from the core, the middle to the rim within the grains, and both the core and the rim contents are low but the middle is high. Electron probe microanalysis shows that the inhomogeneous distribution of water content has no direct relation with the chemical composition of the mineral. Inhomogeneous dislocation is likely to result in the inhomogeneous distribution of structural water in single grain NAMs.