The Evolution Of Xinzhai Basin In Jianshui County, Southeast Yunnan And Its Response To Quaternary Tectonic Movement

Since the late Pliocene,Yunnan area has had complex tectonic movements,frequent crustal squeezing and uneven ascending and descending activities,and at the same time caused inherited deep faults.It is one of the hot spots in the study of regional tectonic evolution in my country.The south section of the Xiaojiang fault zone in Jianshui region in southeastern Yunnan is the southeast boundary fault of the SichuanYunnan block,and plays an important role in regulating regional tectonic movements.It has had strong and distinct activities since the Neotectonic period,and has produced many beaded basins and tectonic landforms along the line,which is an ideal place to study the Quaternary tectonic activities in the southern section of the Xiaojiang fault zone.In this paper,through detailed field geological mapping of the Xinzhai Basin in the southern section of the Xiaojiang fault zone,the main lines are the distribution,lithology and geomorphic characteristics of the stratum inside and near the basin,as well as the distribution,nature and activity time of boundary faults,supplemented by LiDAR Scanning,Sfm,and particle size analysis are used to discuss the genesis of the basin and the characteristics of the period of the neotectonic movement of its response.The main findings are:(1)The boundary faults in the Xinzhai Basin were roughly formed in two time periods: late Early Pleistocene and Holocene.Among them,the faults in the late Early Pleistocene controlled the development of the basin.(2)Linear distribution along the Holocene faults near the Shenxian Cave in the Xinzhai Basin.Combined with the geomorphological characteristics,the “S”-shaped distortion and deformation characteristics are obvious,reflecting the movement characteristics of the left-handed distortion of the Holocene active faults.(3)The Lower Pleistocene is generally missing in the basin,and the Quaternary is mainly distributed in the middle Pleistocene alluvial deposits,residual deposits and residual slope deposits;the Upper Pleistocene slope deposits,residual slope deposits and flood deposits;the Holocene alluvial deposits Objects,lake deposits.A large area of basalt bedrock is exposed in the basin,and the Quaternary sediments are generally thin.It can be considered that the Xinzhai Basin is not the pull apart Basin previously thought.Rather,under the influence of multiple faults and rifts developed by the Yuanmou Movement,the Lujiang River,a tributary of the Nanpan River in the north,and the Red River in the south,converge here,and the wider river valley formed by cutting and erosion was finally formed in the late Pleistocene.Of a water-passing mountain basin.(4)The study area has experienced four stages of tectonic movement since Neogene,which are Neogene,Early Pleistocene,Middle-Late Pleistocene and Holocene.The Neogene was dominated by south-south-east thrusting in the north of the Sichuan-Yunnan block;the crust was uplifted during the Early Pleistocene,the erosion datum level decreased,and the whole was dominated by erosion and leveling.The activity is not obvious;the middle-late Pleistocene period is the intermittent period of fault activity,the fault activity weakens,and the development of the beaded basin along the fault line is completed;the southern section of the Xiaojiang fault zone during the Holocene period is active again,and the activity is penetrated to a certain extent,belonging to a Newly formed fault structure.