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

Fluid inclusions in coesite-bearing eclogites and jadeite quartzite from Sh uanghe and Bixiling in Dabie Shan have been studied in details. At least fi ve types of fluid inclusions can be identified by microthermometry and Rama n analysis: (1) pure N-2; (2) highly brine; (3) CO2(+/-N-2+/-CH4); (4) mixe d CO2-H2O; (5) low-salinity aqueous. Pure N-2 inclusions have been observed only in fresh coesite-bearing eclogites, whereas highly brine inclusions e xist almost throughout the ultrahigh pressure (UHP) metamorphic rocks. Carb onic inclusions occur mainly along and/or near micro-shear zones, or in str ongly deformed jadeite quartzite. Low-salinity aqueous inclusions are limit ed within retrograded UHP rocks, The N-2 and highly brines, first equilibrated at eclogite conditions, are f ar remnants of pre-UHP metamorphic volatiles, re-equilibrated with peak met amorphic minerals at a local scale, corresponding to size of crystal (s). T he carbonic fluids are externally derived, possibly being infiltrated from neighbouring marble or carbonate metasediments. The low-salinity aqueous fl uids may be locally derived from the breakdown of hydrous UHP minerals and exsolution of hydroxyls from nominally anhydrous minerals, or directly intr oduced into the rocks from the country rocks.