大别山榴辉岩（牌楼）P－T－t轨迹

P-T-T PATHS OF ECLOGITES FROM PAILOU,DABIE SHAN.

本文重点研究了大别山潜山，牌楼地区榴辉岩Ｐ－Ｔ－ｔ轨迹，探讨了大别山地区榴辉岩成因，认为榴辉岩原岩主要是碱性玄武岩，少部分洋脊拉斑玄武岩岩浆早期结晶分异堆晶岩及部分钙质沉积岩。它们在华北与杨子板块碰撞时（２６０±３０Ｍａ），地壳向下俯冲到４０－６０ｋｍ处，温度５５０°－８３０°Ｃ，压力１．１－２．１ＧＰａ的条件下形成的。在构造抬升过程中，榴辉岩产生了角闪岩相、绿片岩相退变质作用，角闪岩相温压条件：４６０°－５７０℃，０．４－０．７ＧＰａ。流体包裹体研究表明：流体包体成分主要为ＮａＣｌ－Ｈ＿２Ｏ，Ｈ＿２Ｏ，ＮａＣｌ－ＣＯ＿２－Ｈ＿２Ｏ体系，变质作用过程从早至晚由氧化向还原环境转化。熔融包体的发现表明：榴辉岩形成具有局部深熔作用。从榴辉岩产状、岩石化学、地球化学特征表明本地区榴辉岩不是一种成因，同时具有Ｂ类、Ｃ类榴辉岩特征。

P-T-t paths of eclogites from Pailou,Dabie Shan has been researched and their origin discussedin this paper.The original eclogites mainly derived from cumulate formed by early fractional crystallization ofalkaline basaltic magma and a little oceanic ridge tholeiites,and a part of calsic sedimentary rocks.They maybeformed at temperature 550-830℃,pressurel.1-2.1Gp,when the crust subducted down 40-60Km,related to collision between two continental plates,the North China plate and the Yangtze plate.Eclogites hadexperienced retrograde metamorphism of amphibolite and greenschist facies during processes of tectonic up-lift.The P-T conditions for amphibolite facies are as follows:460-570℃,0.4-0.7Gp.Fluid inclusions mainly are NaCl-H_2O,H_2O,NaCl-CO_2-H_2O system.Composition evolution of fluidinclusions changed from oxidation into reduction in metamorphic processes.Dlscovery of melt inclusionsshows that forming of eclogites has local analexis.According to eclogite occurrence,rock chemistry and geo-chemical characteristics,origin of eclogites in this area is not unique,but of both B and C type.