Fluid Inclusions of Qinglongshan ultrahigh pressure metamorphic eclogite and fluid evolution, north Jiangsu province, China
苏北青龙山超高压变质榴辉岩流体包裹体特征与流体演化

Based on its chemical composition and distribution textural characteristics, five types of fluid inclusions have been distinguished in Qinglongshan Ultrahigh Pressure (UHP) metamorphic eclogites, they are N2-riched fluid inclusions, high-salinity (22.4 to slitely more than23.2wt%NaCl) , moderate-high-salinity(12.6-16.0wt% NaCl) , medium-salinity(6.4-10. 5wt% NaCl) and low-salinity(3. 3-0. 2wt% NaCl) aqueous inclusions. The N2-riched fluid inclusions were trapped during the peak of UHP metamorphism, the high-salinity aqueous inclusions formed during the early stage of exhumation with solid mineral exsolutions, the moderate to high-salinity during high-pressure metamorphic recrystallization, the medium salinity during amphibolite-face retrograde stage, and the low-salinity aqueous inclusions during greenschist-facies metamorphism of the latest stage of uplift. The N2 -riched fluid inclusions present in the peak of UHP metamorhpism and those with high-salinity and moderate to high-salinity during the early stage of exhumation were inherited from the fluids in protoliths by decomposition of NH4 -bearing minerals (or organics) and exsolution of struturally-bound water ( hydroxyl) in nominally anhydrous minerals. The medium-salinity fluids during the late-stage amphibolite-facies meatmorphism were externally-derived in addition to the exsolution of hydroxyl in nominally anhydrous minerals, the low salinity fluids during greenschist facies metamorphism were mainly derived from external source.