Characteristics of fine fluid inclusions in quartz and symplectitic minerals from UHP jadeite quartzite, Dabieshan China: A TEM investigation

摘要

Fluid inclusions at a nano-scale to submicron-scale in quartz and symplectitic corona minerals (albite, taramite and magnetite) from jadeite quartzite at Shuanghe, Dabieshan, China, have been investigated using Transmission Electron Microscopy (TEM). TEM studies indicate that the relationship between coesite and the host quartz is syntaxy and provides strong evidence of the occurrence of high-salty fluids at peak metamorphic conditions, the fluid inclusions less than 350 nm (10 nm-350 nm) in diameter in quartz have negative crystal morphology, irregular or oval. Fluid inclusions in sympletitic albite and magnetite are anhedral, generally less than 200 nm (1 nm-200 nm). Negative crystals in quartz and symplectitic minerals connected to dislocations have also been observed. The above microstructures are undetected at the scale of the optical microscope, representing a possible path for leakage of the fluid phase. The energy-dispersive X-ray spectrometer and TEM analyses confirm that the fluid inclusions in quartz contain CO2, H2O and NaCl, whereas fluid inclusions in symplectitic minerals have CO2, H2O, Al-, and Si-oxide. Therefore, the nano-structures may modify the original composition and density of the fluid inclusions, with significant implications for the correct petrological interpretation.