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

根据青龙山超高压变质榴辉岩中流体包裹体的化学成分、矿物中的分布特征将岩石中的流体包裹体分为五类,即富N2包裹体、高盐度(22.4-略大于23.2wt%NaCl)的NaCl CaCl2 H2O体系流体包裹体、中高盐度(12.6-16.0wt%NaCl)的含Mg2 或Fe2 的NaCl H2O体系流体包裹体、中等盐度(6.4-10.5wt%NaCl)水溶液包裹体和低盐度(3.3-0.2wt%NaCl)的水溶液包裹体。富N2包裹体形成于超高压变质峰期阶段,高盐度的流体包裹体形成于超高压变质岩折返早期固体出溶体出溶阶段,中高盐度的流体包裹体形成于高压变质重结晶作用阶段,中等盐度的流体包裹体形成于角闪岩相变质重结晶作用阶段,低盐度的流体包裹体形成于折返晚期的绿片岩退变质作用阶段。超高压变质峰期阶段和折返早期的高盐度流体和中高盐度的流体主要来自继承原岩中的流体(如含NH4 矿物分解或片麻岩原岩中的有机质分解,名义上无水矿物中羧基水的出溶),晚期角闪岩相退变质阶段的中等盐度的流体除名义上无水矿物中羟基水的出溶外还有外来流体的加入,绿片岩相退变质作用阶段的流体主要为外来流体。

Fluid Inclusions of Qinglongshan ultrahigh pressure metamorphic eclogite and fluid evolution, north Jiangsu province, China

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.