大别山超高压硬玉石英岩中的水:来自红外光谱的证据

为了探讨大别山“名义上无水矿物”(NAMs)中结构水的分布特征, 研究相关的流体活动、矿物变形以及板块俯冲和折返动力学过程提供重要的微观信息.对大别山双河和碧溪岭地区超高压硬玉石英岩中的石英、硬玉、石榴石和金红石进行了傅立叶变换红外光谱(FTIR)分析, 研究结果显示这些矿物都含有以OH-或者H₂O形式存在的氢, 硬玉中结构水平均含量在1000×10-6左右; 石榴石结构水含量在(900~1600)×10-6之间, 各样品颗粒结构水的分布不均匀; 副矿物金红石结构水含量在2000×10-6以上, 而石英结构中基本不含或仅含微量水(< 4×10-6).双河和碧溪岭地区的硬玉石英岩全岩含水量分别为(490~600)×10-6和545×10-6, 不同地区同一种NAMs中结构水含量基本相同.表明在高压-超高压变质岩的形成过程中, 地壳或原岩中的水可以通过这些超高压变质岩中的NAMs携带到地球深部. 

Water in UHP Jadeite-Quartzites of Dabie Mountains: Evidence from Micro-FTIR

The distribution characteristics of structural water in nominally anhydrous minerals (NAMs) from Dabie mountains can provide important microscopic information on some aspects of the related fluid activities, mineral deformation, dynamical process of blocks subduction and exhumation. The NAMs such as jadeites, garnets, rutiles and quarts in ultra-high pressure (UHP) jadeite-quartzites of Shuanghe and Bixiling areas from Dabie mountains were investigated by Fourier transform infrared spectroscopy (FTIR), the result of which indicates that NAMs contain hydrogen occurring as hydroxyl (OH-) or molecule H₂O. It is found that the average structural water contents of the jadeites from the two areas are both close to 1 000×10-6; the rutilezs' are both above 2 000×10-6; the quarts' are both < 4×10-6. The structural water contents of garnets from different grains in the same area aren't uniform, while the water contents of UHP jadeite-quartzites from the two areas both range from 900×10-6 to 1 600×10-6. The results reveal that the water in crust or protolith can be transported into the earth's depth through NAMs in the UHP metamorphic rocks during the formation of the HP-UHP metamorphic rocks.