The Metamorphism And Deformation Of "Lancang Group" In FengQing County,Western Yunnan

Evolutionary history of Changning-Menglian Suture Zone is always the geological research hot spots in home and aboard. There are still many doubts about the stratigraphic subdivision, Characteristics of metamorphic rocks and others of "Lancang Group" in the eastern edge of the southern zone, in Fengqing region of western Yunnan..There were suggest that,based on the field geological profile and survey route, and rock slices research and data of components analysis with comprehensive comparison in this paper:"Lancang Group" The main lithology includes garnet biotite schist, biotite schist, biotite quartz schist, muscovite schist, phyllite, there is a small amount of Granitic mylonite and tectonic schist inside,which experienced the late metamorphism and deformation transformation. There is the invasion of Variscan- Indosinian Permian quartz diorite granite vein. Petrochemical characteristics suggest that its original rocks are felsic rocks and aluminum-rich argillaceous rocks of sedimentary rock."Lancang Group" has a long and complex history of the evolution of metamorphism and deformation. There are three period deformations and three period metamorphism:The first period of metamorphism- deformation(D1M1) is mainly on bedding compression effect, forming sharp edge- thick top- tight folds, regional foliation S1 is formed; metamorphic grade is strong. It belongs to low-amphibolite facies and regional dynamic thermal metamorphism. The curtain is main metamorphism of the schists in "Lancang Group". The main metamorphic mineral paragenetic association is:(Schists): Garnet(Gar) + plagioclase(Pl) + biotite(Bi) + quartz(Q);(phyllite class): sericite 1(Ser) + albite(Act) + quartz(Q).The second period of metamorphism- deformation(D2M2) is mainly on the level of contraction effect, forming regional fold axial plane cleavage and slip cleavage S2, metamorphic grade is weak. It belongs to low-amphibolite facies toward low greenschist facies regional dynamic thermal refund metamorphism. The main metamorphic mineral paragenetic association is:(Schists): albite(Act) + muscovite(Mus) + chlorite(Chl) + quartz(Q);(phyllite class): sericite 2(Ser) + chlorite(Chl) + quartz(Q).The third period is deformation before metamorphism(D3M3): it is mainly on the base slip ductile deformation effect, deformation has a Shallow- table structure level features. The small superimposed folds and crenulation lineations developed well,shear foliation S3 has a non-penetrative characteristics. Metamorphic grade is uneven, fault zone is mainly on brittle- ductile dynamic metamorphism, it belongs to low greenschist facies, The main metamorphic mineral paragenetic association is: sericite 3(Ser) + quartz(Q).According to the regional geological background and Tectonic characteristics speculate that the first period of metamorphism-deformation of "Lancang Group" occurred in the Variscan- Indosinian,with Oceanic crust of Changning- Menglian ocean subduction stage; the second period of the evolution occurred in Variscan- Indosinian, after Changning- Menglian ocean crust subduction, Gondwana land and Yangtze blocks continent- continent collision stage; the third period occurred in the Himalayan,uplift of the Lancang River fault zone, which occurred Brittle- ductile shear orogeny.