The Analysis Of Sedimentation And Structural Characteristics Of Early Haixi Devonian System In Mengtong Area Of West Yunnan Province

The region of Meng Tong,in western Yunnan,straddles Gondwana land and Laurasia land.And it locates in the bending of east side of Tethys tectonic region.This region,which is a comprehensive scientific research center into geology,not only maintains the primary record of sediments in oceanic basin but also displays clearly the geological tectonic characteristics in both sides.Devonian periods is the starting phrase for Paleo-Tethys Ocean.The blocks of Baoshan-Zhenkang and Shangyangzi became independent blocks in succession,during which they were divided by the Changning-Menglian oceanic basin,the principal branch of Paleo-Tethys Ocean.In the early Hercynian period,the east of west sides of Meng Tong region was divided into Baoshan-Zhenkang and Shangyangzi blocks respectively with the Changning-Menglian oceanic basin as its enter.The thesis chooses Meng Tong region as its research subject,and it is armed with the the influence of structural feature on depositional environment reginal tectonic revolution as its principle guideline,integrating the sedimentary-tectonic-reginal revolution closely.Based on the comprehensive investigation into surface geology,combining lithofacies paleogeography and structural features materials,this thesis detailedly analyzes the petrological types,sedimentary facies and sedimentary patterns in each group,and the tectonic features,deformation characteristics and metamorphism in each tectonic unit of the Devonian in the early Hercynian period of Meng Tong region.It is concluded that the tectonic activity in the study area is relatively stable during the Devonian period,and the Baoshan-Zhenkang block and the upper Yangtze plate exhibit different sedimentary tectonic environments.In the early Devonian period,Group Xiangyang Temple in Baoshan-Zhenkang block developed a formation of a set of shallow sea-semi deep clasolite-carbonate rocks-silicolite;in the mid-to-late Devonian period,it developed a formation of a set of shallow sea-platforms carbonate rocks.Group Hot Spring in Changning-Menglian oceanic basin developed a formation of shallow sea-semi deep clasolite-silicolite,with upper coal-bearing formation.The uplift of the Shangyangzi is resulted by the expansion of Changning-Menglian current,at the same time,Shangyangzi developed a formation of littoral-shallow sea and clasolite in Group South Phrase.Besides,this paper also discusses both the transverse and longitudinal sedimentary problem of Group Xiangyang Temple and the connection between the late deformation and metamorphism of Group Hot Spring and Group South Phrase in Baoshan-Zhenkang block;and the tectonic evolution of the study area in the early Hercynian period was discussed too.On the basis of research above,in the early Hercynian period of Meng Tong region,the influence of the tectonic characteristics of Devonian on the sedimentation was clarified.