The Study of Microstructure Characters and the Condition of Metamorphism and Deformation of Garnets from Garnet-Mica Schist in the Tongbai Moutain, East Section of Shangnan-Danfeng Fault Belt

To study the metamorphic—deformation condition of rocks in ductile of shear zone is an important step to investigate the orogenic process and mechanism.Microstructure and ultrastructure characters of minerals in rocks are true indications of deformation condition of the orogenic belt,and are the basis of the research on the deformation of orogenic belt.Based on the study of characteristics of dislocations and the types of dynamic recrystallization of garnets in garnet—mica schists in Tongbai Moutain,east section of Shangdan fault(Shangnan—Danfeng fault) belt,the types of the plastic deformation,the deformation mechanism and the condition of deformation of garnets are identified.Dislocations of garnets are mainly free dislocations and dislocation walls,and dislocation movement are mainly slips,slip planes are 1 /2 111 {110} and 100 {001}.The dynamic recrystallization of garnets is due to the subgrain growth and boundary migration.Formation condition of garnet mica schist is estimated:the temperature is 562~617℃,and the pressure is 0.77~1.02 GPa.Free dislocation density is 6.14×108/cm2,the differential stress is 0.511GPa and strain rate is 4.97536× 10-10 m/s.After systematic analysis we can draw a conclusion that there are some relationships between dislocation characters and the formation and evolution of the tectonic belt.The garnets had been subjected to early medium-grade regional metamorphism,then formed dislocations with high density and subgrains under the strong stress in the formation of shear zone,finally occurred plastic deformation and the bulging recrystallization which formed in the period of heat relaxation which had a relatively low stress.