江苏东海预先导孔(CCSD-PP1)超高压岩石变质流体及其演化  

Metamorphic Fluids and Its Evolution in the UHP Rocks from the Pre-pilot Hole of Jiangsu Province, China

作　　者：沈昆 张泽明[2] A.M.vandenKerkhof 肖益林 J.Hoefs 

机构地区：[1]山东省地质科学实验研究院,济南250013 [2]中国地质科学院地质研究所,北京100037 [3]哥廷根大学地学中心,德国哥廷根37077

出　　处：《地质学报》2003年第4期522-532,共11页Acta Geologica Sinica

基　　金：中国大陆科学钻探工程的部分研究成果;得到了科技部重大基础研究前期研究专项(编号 2001CCB00900);国土资源部科技项目(编号 2002207);中国地质调查局地调项目(编号 150C002004);德国国家科学基金(DFG;Ho 375/22);中国地质科学院地质研究所大陆动力学实验室资助

摘　　要：中国大陆科学钻探工程预先导1孔(CCSD-PPH1)位于大别—苏鲁超高压变质带东段的江苏东海县,孔深为432 m,其岩心为一套变质表壳岩、花岗质片麻岩和镁铁-超镁铁质侵入岩。它们经历了超高压变质作用和随后的角闪岩相退变质作用。这些岩石中存在四类流体包裹体:①中高盐度CaCl_2-NaCl-H_2O包裹体(Ⅰ型),宿主为榴辉岩中的石榴子石、绿辉石和蓝晶石石英岩中的蓝晶石,可能代表了峰期变质流体;②H2O-CO_2(±N_2)-NaCl±固体的包裹体(Ⅱ型),宿主为榴辉岩中的石英和蓝晶石石英岩中的蓝晶石,可能为超高压岩石折返和退变质期间带入岩石的流体;③中—低盐度水溶液包裹体(Ⅲ型),产于蓝晶石石英岩、榴辉岩和片麻岩中。蓝晶石石英岩中的包裹体是部分继承了俯冲阶段变沉积岩脱水-脱挥发分流体;榴辉岩和片麻岩中的中-低盐度水溶液包裹体主要是角闪岩相退变质期间或更晚期捕获的;④中-低密度的富CO_2包裹体(Ⅳ型),沿蓝晶石石英岩石英中的(切)穿颗粒裂隙分布。根据包裹体显微测温数据,从Ⅰ型包裹体的等容线得到的压力值大大低于根据矿物温压计获得的压力。这表明大多数Ⅰ型包裹体的组成和密度在捕获后均发生了不同程度改变。这些变化包括渗漏、部分爆裂和流体-岩石相互作用等。流体包裹体研究也表明本区超高压变质作用峰期流?Drill cores from the first pre-pilot hole of the Chinese Continental Scientific Drilling Project (CCSD-PPH1) located in the eastern part of the Dabie-Sulu UHP metamorphic belt consist of a rock association of metamorphic supracrustal rocks, granitic gneiss, and mafic and ultramafic intrusives. These rocks, except the garnet peridotite, have been subjected to an eclogite-facies UHP metamorphic event followed by a later amphibolite-facies retrometamorphism. The metamorphic p-t conditions for the coesite-bearing eclogite and eclogitic gneiss were 785~820℃ and >2. 7 GPa. Four types of fluid inclusions have been distinguished: (1) High-salinity CaCl2-NaCl-H2O inclusions (type Ⅰ) in garnet and omphacite from eclogite, and in kyanite from kyanite quartzite, probably representing the peak metamorphic fluids. (2) Inclusions containing mixed H2O-CO2(±N2) -NaC1(other solids (typeⅡ) , which occur in quartz from eclogite and in kyanite. They may reflect the fluids which were introduced during the exhumation and retrometamorphism. (3) Inclusions containing aqueous solutions of low salinity in the kyanite quartzite (type Ⅲ) have partly inherited the fluids released from dehydration-devolatiliztion of metasediments during the subduction, whereas those containing aqueous solutions of medium-low salinity (type Ⅳ) in eclogites and gneisses have been trapped during the amphibolite-facies retrometamorphism or a later stage. (4) CO2-rich inclusions (type Ⅴ) are distributed along the transgranular fractures of quartz in kyanite quartzite and may have formed by retrapping of leaked H2O-CO2 fluids. The pressure derived from the isochores of type Ⅰ inclusions is much lower than that obtained from the mineral thermobarometer. This implies that most of type Ⅰ inclusions have undergone changes in density after the trapping. In a rare case, high-density type Ⅰ inclusions may produce isochores that correspond to the eclogite-facies metamorphism. Fluid inclusion data also suggest that the fluid system was more or less closed

关 键 词：超高压岩石 变质 流体 演化 苏鲁造山带 

分 类 号：P588.3[天文地球—岩石学]