Unusual high-density and saline aqueous inclusions in ultrahigh pressure metamorphic rocks from Sulu terrane in eastern China

Primary high-density fluid inclusions were identified in garnet from ultrahigh pressure eclogite in the southern part of the Sulu terrane. They occur isolatedly or in cluster together with relatively low-density two-phase inclusions. The eutectic temperature of the inclusions is as low as less than or equal to-52degreesC. A bubble was nucleated in a liquid inclusion during the specific stage of cyclic cooling-heating runs, and the liquid-gas homogenization temperature was measured to be less than or equal to-12.5degreesC. The composition of the inclusions modeled by the system CaCl2-NaCl-H2O, yields the fluid density of 1.27 g/cm(3) that corresponds to a pressure of ca. 2.4 GPa at the temperature of peak eclogite-facies metamorphism, close to the ultrahigh pressure metamorphic conditions. During the exhumation of the eclogite the inclusions reacted with the host mineral, forming hydrous silicate minerals that resulted in lowering of the fluid density and its transformation to multi-phase inclusions.