Metamorphic Characteristics Of Mengtong Metamorphic Rocks,Western Yunnan

Mengtong Metamorphic Rocks is in the south section of Changning-Menglian suture zone have always been the focus of research.The strata han been divided into Yungou Formation and Wangyayan Formation.There are some difference in this rocks,but it's stratum is sequential,and it's metamorphism and deform ation is sequential too.so this rocks are called Mengtong Metamorphic Rocks in the this paper,used for restore the evolution of Baoshan Blcok and Changning-Menglian suture zone.Varies metamorphism and deformation are finded in this rocks that conposed biotite schist and biotite quartz schist,and tectonic biotite schist and mylonitiz ation biotite quartz schis in deformation.The first metamorphism mineral parage nesis is garnet-garnet-biotite-feldspar-quartz in the epidote amphibolite facies.The second is kyanite-garnet-biotite-quartz-feldspar.Kyanite appeared also kyanite and staurolite coexisted in amphibolite facies.The third is Garnet-biotite-quartz in greenschist facies.There are also three deformations,New foliation(S1)is formed in the first concurret metamophic deformation(M1-S1),S1 and metacrystal has been deformed in the second time(M2-S2).Main schistosity(S3)is crenulation cleavage recrystallization in the third time(M3-S3).mylonites are formed by ductile deformation in differential uplift period.Those mineral paragenesis is sericite-quartz.Mengtong Metamorphic Rocks's metamorphism is fortified downward,it's deformation is intensive later.These characteristics are the same as the orogenic metamorphism.The protolithes,clastic rocks in passive continental margin,are formed in Neoproterozoic at later.The first metamorphism is determinded regional thermal-dynamic metamorphism in Jinning Period(Neoproterozoic,isotopic age(U-Pb)951�7Ma),The second,regional dynamic-thermal metamorphism in Caledonian Period(Middle Ordovician,(U-Pb)463�2Ma).And regional low temperature dynamic metamorphism occurred in Indosinian Period(late Triassic).Regional differential uplift has resulted in ductile deformation and weak metamorphic crystallization in some rocks since the Yanshan period in this paper.