大别山金河桥超高压榴辉岩石榴石中的水

名义上无水矿物的水含量研究对于认识俯冲带流体活动和地球动力学具有重要意义.对大别山金河桥榴辉岩中石榴石进行了傅里叶变换红外光谱分析和主微量元素分析，结果表明石榴石含有分子水和结构羟基，分别为 < 1×10-6~1 946×10-6和< 1×10-6~1 347×10-6.石榴石羟基含量与Ca、Na、Ti、Zr和Pr正相关，而与Si负相关，表明羟基结合机制以水榴石替代为主并伴有其他机制.分子水主要为初始水或折返过程中羟基转化形成.石榴石总水含量为 < 1×10-6~3 293×10-6，最大值对应于峰期超高压石榴石水储存能力.水在峰期石榴石中可达到饱和.石榴石变化的水含量受原岩性质、流体可获得性、压力和温度等多种因素控制，但主要由折返过程中降压脱水导致.石榴石平均总水含量为749×10-6~1 164×10-6，是俯冲板片向地幔水传输的重要介质. 

Water of Garnet in Eclogite from Jinheqiao Area in the Dabie Orogen

Nominally anhydrous minerals (NAMs) are major components of the subducted continental slab and thus regarded as important water reservoir in continental subduction zone. The water contents of NAMs are critical for understanding of fluid action and geodynamics of subduction zones. In this study,Fourier Transform Infrared Spectroscopy (FTIR) as well as major and trace element analyses were carried out on garnets in Jinheqiao eclogites from the Dabie orogen. The results demonstrate that garnet grains contain molecular water and hydroxyl (OH) with the contents of < 1×10-6 to 1 946×10-6 and < 1×10-6 to 1 347×10-6,respectively. Contents of hydroxyl are positively correlated with Ca,Na,Ti,Zr and Pr,but negatively correlated with Si for garnets in most samples,indicating that the incorporation of OH in garnet is dominated by hydrogarnet substitution. Molecular water is primary or transformed from hydroxyl during exhumation,implying molecular water an internal origin in eclogite. Garnet has total water contents varying from < 1×10-6 to 3 293×10-6,with the highest water content corresponding to the garnet's capacity for water storage under peak UHP metamorphism. Water can be saturated in peak metamorphic garnet. The variable water contents in garnet have been controlled by several factors including protolith nature,fluid availability,pressure and temperature,which however,have been dominated by decompression dehydration during exhumation. Garnets in the Jinheqiao eclogites have average total water contents ranging from 749×10-6 to 1 164×10-6,suggesting that they have similar capacity for water storage as omphacite and thus are important media for subducted slab to transport water into deep mantle.