Submicron-sized fluid inclusions and distribution of hydrous components in jadeite, quartz and symplectite-forming minerals from UHP jadeite–quartzite in the Dabie Mountains, China: TEM and FTIR investigation

Submicron-sized fluid inclusions and distribution of hydrous components in jadeite, quartz and symplectite-forming minerals from UHP jadeite–quartzite in the Dabie Mountains, China: TEM and FTIR investigation Original Research Article Pages 517-526 Dawei Meng, Xiuling Wu, Xiaoyu Fan, Xin Meng, Jianping Zheng, Roger Mason Close Close preview | Purchase PDF (1178 K) | Related articles | Related reference work articles AbstractAbstract | Figures/TablesFigures/Tables | ReferencesReferences Abstract Fluid inclusions and clusters of water molecules at nanometer-to submicron-scale in size have been investigated using transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) in jadeite, quartz and symplectite aegirine–augite, albite, taramite and magnetite corona minerals from ultrahigh-pressure (UHP) jadeite–quartzite at Shuanghe, the Dabie Mountains, China. Fluid inclusions from 0.003 μm to 0.78 μm in size occur in jadeite and quartz crystals, and a small number of fluid inclusions from 0.001 μm to 0.25 μm have also been detected in symplectite-forming minerals. Most of the fluid inclusions have round or negative crystal morphology and contain aqueous fluids, but some contain CO2-rich fluids. They are usually connected to dislocations undetectable at an optical scale. The dislocations represent favorable paths for fluid leakage, accounting for non-decrepitation of most fluid inclusions when external pressure decreased at later stages, although there was partial decrepitation of some fluid inclusions unconnected to defect microstructures resulting from internal overpressure. Non-decrepitation and partial decrepitation of fluid inclusions resulted in changes of original composition and/or density. It is clear that identification of hidden re-equilibration features has significant implications for the petrological interpretation of post-peak metamorphic processes. Micro-FTIR results show that all jadeite and quartz samples contain structural water occurring as hydroxyl ions (OH−) and free water (H2O) in the form of clusters of water molecules. The H2O transformed from OH− during exhumation and could have triggered and enhanced early retrograde metamorphism of the host rocks and facilitated plastic deformation of jadeite and quartz grains by dislocation movement, and thus the H2O released during decompression might represent early-stage retrograde metamorphic fluid. The nominally anhydrous mineral (NAM) jadeite is able to transport aqueous fluids in concentrations of at least several hundred ppm water along a subduction zone to mantle depths in the form of clusters of water molecules and hydroxyl ions within crystals. Article Outline 1. Introduction 2. Samples and analytical methods 3. Results 3.1. Fluid inclusions in quartz and jadeite 3.2. Fluid inclusions in symplectite-forming minerals 3.3. IR spectroscopy analyses of the jadeite and quartz 3.4. Clusters of water molecules in the minerals 4. Discussion 4.1. Submicron-sized fluid inclusions in quartz, jadeite and symplectite-forming minerals 4.2. Water in UHP metamorphism and retrograde metamorphic processes 4.3. Role of the OH/H2O in the natural deformation of minerals 5. Conclusions Acknowledgements References