Cenozoic Deformation Of Yaoshan Group In The West Of Yunnan Province And Day Nui Con Voi In The Northwest Of Vietnam And Their Geological Implication

Much attension has been paid to the Ailao Shan-Red River shear zone as an important structural accommodation zone during the subsequent India-Asian collision, but the Yaoshan Group in the northeast of the Red River shear zone is not so well researched. With comparison of Yaoshan Group and Day Nui Con Voi Group in the Manhao-Hekou-Lao Cai-Viet Triv, the Cenozoic deformation history of Yaoshan Group is studied in this dissertation, which gives evidence for the Ailao Shan-Red River shear zone evolvement in Cenozoic.Yaoshan Group in the west of Yunnan Province and Day Nui Con Voi Group in the northwest of Vietnam locates between Song Hong fault zone and Song Chay fault zone, extending in NW-SE direction. Yaoshan Group and Day Nui Con Voi Group, as a large-scale anticline, are metamorphic complexes at amphibolite facies. In the groups the most intensity deformation reserved is the strike-slip shear deformation during the Cenozoic, and the structural character of lines and plans is consistent with that of Ailao Shan-Red River shear zone. At aspects of mineral combination, mineral growth sequences, character of metamorphism and deformation in rocks, temperature and pressure of metamorphism and deformation, Yaoshan Group can be well compared with Day Nui Con Voi Group, indicating that they experienced same structural evolvement during Cenozoic.Based on previous work, two geological sections, and four measured sections and combined with microtectonic analysis and temperature and pressure tests of metamorphism and deformation, this dissertation argures that Yaoshan Group and Day Nui Con Voi Group experienced two periods of left-lateral strike-slip shearing and a period of right-lateral strike-slip normal faulting.Compared deformation of Yaoshan Group and Day Nui Con Voi Group and combined with tectonic features of Ailao Shan-Red River shear zone, this dissertation argues that Ailao Shan-Red River shear zone started left-lateral strike-slip shearing during 39Ma~34Ma. Based on previous work and temperature and pressure testing results and deformation characters, this dissertation argues that Yaoshan Group and Day Nui Con Voi Group started to be cooled and denudated during 39Ma~34Ma with the peak metamorphic condition of ~720℃and 0.7±0.1 GPa, forming various kinds of inner layer A-type folds and boudins. During 28Ma~17Ma the relevant deep metamorphic plutons were further lifted by the activity of Ailao Shan-Red River shear zone, which can be divided into two steps: primary slow lifting and later fast lifting. As to Yaoshan Group and Day Nui Con Voi Group, they were slowly cooled and lifted during 28~25Ma; during 25~21Ma the rate of cooling and lifting were speeded and the metamorphic facies was changed from low amphibolite to green schist facies, temperature from 500℃to 300℃, pressure from 0.5 GPa to 0.3 GPa, mylonizing the groups. From ca 5Ma, the Red River shear zone started right-lateral strike-slip normal faulting, which forms small scale right-lateral shear zones, granitic plutons in the shear zones in Yaoshan Group and kinking in local regions at low green schist facies.