Study On Petrological Characteristics And Engineering Problems Of Luang Prabang Suture Zone Of China Laos Railway

The China-Laos railway project,as a key project of the "Belt and Road",is a link project for enhancing political and economic exchanges between my country and Laos.The Luang Prabang suture zone of the China-Laos Railway is one of the most difficult sections.As a newly identified tectonic belt,the Luang Prabang suture zone is located between the Simao plate and the Indosinian plate.Rock formations of different ages,different sequences,and different origins are mixed together.Whether it is a plate suture zone,tectonic evolution and strike connection are still controversial.In addition,Laos’ poor economic foundation and lack of basic geological data pose a great threat to the construction and operation of railway projects.Relying on the research project of the China-Laos Railway Project and combining the existing data in this area,this paper conducts zircon U-Pb chronological tests and geochemical tests on the exposed volcanic rocks in the belt,and analyzes the controversial geological problems in the Luang Prabang suture zone.Analyze and demonstrate.The main reasons for the engineering geological problems of the Luang Prabang suture zone of the China-Laos Railway are analyzed from the perspective of lithology and tectonic deformation.The following main conclusions were reached:(1)The age of acid volcanic lava dacite is 229.3±0.78 Ma,and the formation age of intermediate-basic volcanic rock is about 240Ma-260 Ma.The chronology and geochemical characteristics indicate that the volcanic rocks in the Luang Prabang suture zone formed a threephase formation pattern of oceanic crust-island arc-continental arc.The subduction and closure of the Luang Prabang back-arc basin continued until the Late Triassic,which improved the Luang Prabang back-arc basin.The tectonic evolution model of the Prabang suture provides new evidence for the properties of the Luang Prabang suture.(2)The lithology of the Luang Prabang suture zone of the China-Laos Railway is dominated by sandstone,slate and basalt,and limestone is developed in local sections.The engineering problems mainly focus on the boundary fault of the Luang Prabang suture zone.The lithology revealed by the construction excavation is different from the survey and design stage,but there is a similar lithological combination with the interior of the suture zone.It is believed that the northern boundary is more likely to be Pubadaoshan fault.(3)The characteristics of tectonic deformation indicate that the strain of the Luang Prabang suture should be concentrated on the boundary faults of the suture,and the faults inside the suture hardly bear the strain distribution,which leads to engineering problems focusing on boundary faults under the condition of similar lithology.It is proposed that the future construction of linear projects passing through the Luang Prabang suture should focus on the prevention of geological hazards at the north-south boundary fault.