The DCS Metamorphic Complex Western Yunnan:the Spatial-temporal Framework Of Granitic Rocks And Cenozoic Metamorphism-deformation

As the boundary between the Yangtze block and the Lanping-Simao-indosinia block,the Ailao Shan-Red River(ASRR)tectonic belt is a zone of tectonic weakness during its tectonic history.The ASRR belt suffered multi-phase of tecotono-thermo events,which has been a topic of intensive study in the last decades.The Diancang Shan metamorphic complex is one of the four metamorphic complexes of the ASRR tectonic belt,which provides a typical example for a deep understanding of the tectonic evolution of the belt.This thesis finished U-Pb dating of magmatic(LA-ICP-MS)and metamorphic(SHRIMP)zircons from different parts of complex.Neoproterozoic magmatic ages(765.612.7Ma.766.1±2.OMa)and early to middle Triassic(240-250Ma)were obtained from the magmatic rocks intruding the eastern part of the complex.Through regional comparison and analysis it is shown that the eastern part of the Diancang Shan metamorphic complex is a part of Yangtze block.Mylonitized granitic rocks from the south-western granitic mylonite zone of Diancang Shan metamorphic complex have early to middle Triassic magmatic ages.The magmatism was probably resulted from the Paleo-Tethys oceanic plate subduction below the Lanping-Simao-Indosinian blocks.With the Cenozoic deformation-metamorphic evolution as another major topic of study,this thesis also focuses on the high grade metamorphic aluminous rocks,i.e.the sillimanite-garnet-biotite gneiss.Through microscopic structural analysis and paragenetic association study,an upper amphibolite facies assemblages of garnet+sillimanite + K-feldspar + biotite + plagioclase±quartz and a lower pressure amphibolite facies assemblage of sillimanite + muscovite + biotite + quartz were recognized in the high grade metamorphic aluminous rocks.SHRIMP U-Pb dating of metamorphic zircons from the high grade gneiss reveals Cenozoic growth of the zircons during three stages of metamorphism,i.e.at ca.54.2±1.7Ma,31.5±1.5Ma and 27.5 ± 1.2Ma.Structural analysis on early to middle Triassic granitic rock and Cenozoic granitic mylonite hosted in Diancang Shan metamorphic complex suggests that solid state plastic deformation and strain localization is the main feature of middle crust flow along the ASRR tectonic belt.LA-ICP-MS magma zircon U-Pb chronology experiment was carried out for fine grained granitic mylonite intruding the granitic mylonite zone of the southwestern part of the complex and granitic mylonite intruding the eastern part of the complex and fine granitic mylonite dyke located in the aluminous metamorphic rocks zone in the middle part of the complex.Early,middle and late Oligocene(30.171±0.28Ma.27.37±0.2Ma?24.410.89Ma)of magmatic emplacement is shown from the study.From the multi-stage apparent age populations of metamorphic zircons 2150Ma-27Ma from a sillimanite-garnet-biotite gneiss,it is shown that the metamorphic rocks from the ASRR tectonic zone has a complex tectonic evolution.Combined regional research and three stages of metamorphic age populations of metamorphic zircons from the sillimanite-garnet-biotite gneiss and three stages magma intruding age populations of magma zircons of granitic rocks which hosted in the three parts of Diancang Shan metamorphic complex.it is shown that the multi-stage and multi-phase of Cenozoic thermal-tectonic evolution of the Red River Ailao Shan tectonic zone which is attributed to the Indian-Eurasian plate convergence and plate collision(ca.54 Ma),post-collisional extension(ca.40 Ma to 30 Ma)and large scale left-lateral shearing along the Ailao Shan-Red River shear zone(ca.27-21Ma).