山东沂水麻粒岩杂岩中的变质流体及地质意义

Metamorphic Fluids in the Yishui Granulite Complex and Their Geological significance,Shandong

山东沂水麻粒岩杂岩中含有大量高密度富ＣＯ＿２流体包裹体，伴随有ＣＯ＿２－Ｈ２Ｏ，ＣＯ＿２±Ｎ＿２±ｃＨ＿４的包裹体。对这些包裹体的产状、分布和组成等特征进行了详细的岩相学研究，并选择有代表性样品进行了显微测温和激光拉曼探针分析。结合本区地质和岩石学研究成果确定沂水麻粒岩杂岩峰期变质温度为８００℃，压力为０．７５ＧＰａ。对变质流体组成、演化及其成岩意义也进行了讨论。

The Yishui granulite complex of middle to late Archaean (with isotopic ages ranging be-tween 3000 Ma and 2500 Ma)consists of the supracrustal rocks of Yishui Group and its in-truded charnockites-granitoids. The petrography,microthermometry and Raman microprobe analysis of fluid inclusions have shown that the granulite complex contains inclusions of CO_2-rich(Ⅰ), N_2±CH_4±CO_2(Ⅱ),CO_2-H_2O( Ⅲ )and H_2O(Ⅳ).Most inclusions occur in trails(healed fractures),quartz,garnet and plagioclaes except some dense CO_2-rich inclusions(Ⅰa)and minor type Ⅱ inclu-sions which occur as isolated ones or in clusters. In biotite-two pyroxene gneiss and garnetcharnockite of the highest metamorphic grade,the type Ia inclusions are more abundant,containing near pure CO_2 fluid(Twco_2 are close to-56.6℃,the triple point of CO_2) and hav-ing the highest density(Thco_2 can be as low as -34℃,corresponding to 1. 095g/cm￣3);whereas in charnockite, monzogranite and tonalitic granite, the type Ia inclusions are de-creased in abundance,containing significant amount of N_2(Tmco_2=-58.8～-56.8℃) andhaving lower density(Thco_2=-30～+17℃,corresponding to dco_2=1.07～0. 8g/cm￣3),while the quantities of type Ⅱ, Ⅲ and Ⅳ inclusions are increased gradually. This reflects aregular variation of fluid compositions at different levels of the middle-lower crust in the re-glon.The mineral thermometry and fluid inclusion studies have shown that the peak metamor-phic conditions of granulite facies in the region are T = 800±50℃ and p=0.75GPa,Mean-while the charnockite,monzogranite and tonalitic granite have experienced metamorphic con-ditions of 700℃,0.6GPa;500℃,0.4 GPa and 450℃,0.2～0.3 GPa respectively, thus sug-gesting a clockwise p-T path convex to the temperature axis. The ubiquitous presence of the CO_2-rich inclusions in the granulite complex regardless ofrock types indicates that CO_2 fluid may not be coritrolled by local mineral equilibria and mayhave an external source,whereas N_2 and aqueous fluids may be controlled by lithology andcome from the middle to upper crust by metamorphic dehydration-devolatilization reactionsas well sa by addition of near-surface water.