Fluid inclusions in ultrahigh pressure metamorphic rocks from Shuanghe and Bixiling in Dabie Shan.

Fluid inclusions in coesite-bearing eclogites and jadeite quartzite from Shuanghe and Bixiling in Dabie Shan have been studied in details. At least five types of fluid inclusions can be identified by microthermometry and Raman analysis: (1) pure N-2; (2) highly brine; (3) CO2(+/-N-2+/-CH4); (4) mixed CO2-H2O; (5) low-salinity aqueous. Pure N-2 inclusions have been observed only in fresh coesite-bearing eclogites, whereas highly brine inclusions exist almost throughout the ultrahigh pressure (UHP) metamorphic rocks. Carbonic inclusions occur mainly along and/or near micro-shear zones, or in strongly deformed jadeite quartzite. Low-salinity aqueous inclusions are limited within retrograded UHP rocks, The N-2 and highly brines, first equilibrated at eclogite conditions, are far remnants of pre-UHP metamorphic volatiles, re-equilibrated with peak metamorphic minerals at a local scale, corresponding to size of crystal (s). The carbonic fluids are externally derived, possibly being infiltrated from neighbouring marble or carbonate metasediments. The low-salinity aqueous fluids may be locally derived from the breakdown of hydrous UHP minerals and exsolution of hydroxyls from nominally anhydrous minerals, or directly introduced into the rocks from the country rocks.