Fluid inclusions in coesite-bearing eclogites and jadeite quartzite at Shuanghe, Dabie Shan (China)

Fluid inclusions in coesite-bearing eclogites and jadeite quartzite at Shua nghe in Dabie Shan, East-central China, have preserved remnants of early, p rograde and/or peak metamorphic fluids, reset during post-UHP (ultrahigh-pr essure) metamorphic uplift. Inclusions occur in several minerals (e.g. omph acite & epidote), notably as isolated. primary inclusions in quartz include d in various host minerals. Two major fluid types have been identified: non -polar fluid species (N-2 or CO2) and aqueous, the latter is by far the mos t predominant. Aqueous fluids cover a wide range of salinity, from halite-b earing brines to low salinity fluids. For non-polar fluids, few N-2 inclusi ons occur in undeformed eclogite, whereas a number Of CO2-rich inclusions h ave been found in microshear zones of eclogite or jadeite quartzite in clos e proximity to marble occurrences. The primary character of N-2 and high-salinity aqueous inclusions indicates that they are remnants from UHP metamorphic fluids and for some there is t he distinct possibility that they are ultimately derived from pre-metamorph ic fluids. This conclusion is supported by the preservation. in some sample s, of microdomains containing synchronous inclusions of variable salinities , which tend to relate to the chemical composition of the host crystal. Car bonic fluids may be derived from neighbouring rocks, notably marble and car bonate-bearing metasediments, during post-metamorphic uplift. During post-U HP exhumation, a limited decrease of the fluid density has occurred, with f ormation of new sets of fluid inclusions. Fluid movements, however, remaine d exceedingly limited, at the scale of the enclosing crystal.