Characteristics And Dynamic Mechanisms Of Mesozoic Structural Deformation In The Qinzhou-Lingshan Structural Zone

The Qinzhou-Lingshan structural zone,formed in the southern part of South China plate,is a Mesozoic intraplate tectonic-magmatic activity zone in Guangxi.All kinds of evidences show that Qinzhou-Lingshan structural zone has a complex tectonic background,not only serves as the tectonic boundary on the northwest side of Qinlian-Luoding aulacogen,but also the South China intraplate largest magnitude earthquake recorded in the Lingshan segment of the Qinzhou-Lingshan structrural zone-the 1936 Ms6³/₄ Lingshan earthquake and its seismic surface rupture zone.Therefore,structural analysis research on the Qinzhou-Lingshan structrural zone can not only provide structural evidence for the extension and structure of the southern segment of the Qinzhou-Hangzhou junction belt,but also put forward new perspectives and understandings on the converging process of the Yangtze block and Cathaysian block in southern of South China plate and the Mesozoic intraplate orogenic pattern in the southern section of the Qinzhou-Hangzhou junction belt.This article selects the Lingshan segment of the Qinzhou-Lingshan structrural zone as the key analysis area,and combines the interpretation of regional tectonic mapping and geophysical data.The specific analysis results are as follows:（1）The Lingshan segment of Qinzhou-Lingshan structural zone is mainly composed of three groups of structures with different stages and different properties,including Lingshan strike-slip structure,Luoyangshan thrust nappe structure and Lemin-Zhaixu extension structure.The Lingshan strike-slip structure has thrust-translate characteristics,showing a group of parallel or branch composite strike slip fault on the plane,and a positive flower structure converging to the deep on the profile.The Luoyang Mountain thrust nappe structure overthrust the Liuwandashan granite body onto the autochthonous Paleozoic strata,showing an northwestward arc-shaped composite fault on the plane,and a dual thrust nappe structure composed of the front and back margin nappe type ductile shear zone and Lenticular granite fault block on the profile.The Lemin-Zhaixu extensional structure is composed of the extensional ductile shear zone at the top of granite core,the tensional dike swarms and the large tensional fault.（2）Under the geological background of the closure of the Qinlian-Luding aulacogen in the late Paleozoic,the Yangtze block and the Cathaysian block underwent oblique amalgamation-intraplate orogeny along the Lingshan segment of the Qinzhou-Lingshan structural zone in the Mesozoic.In the early Mesozoic,the Yangtze block and the Cathaysian block underwent oblique amalgamation-intraplate orogeny,resulting in the formation of a thrust-translate Lingshan flower strike-slip structure.In the middle term,due to the continuation of oblique amalgamation-intraplate orogeny,the Liuwandashan granite body on the southeast side of Qinzhou-Lingshan structural zone was thrust over the Paleozoic strata,forming the Luoyang Mountain double thrust nappe structure.In the late stage,the whole Qinzhou-Lingshan structural zone changed from the compression-thrust stage to the post-orogenic extension stage,forming the Lemin-Zhaiwei post-orogenic extension structure.（3）The Qinzhou-Lingshan structural zone,as the main location of the southern part of the Qinzhou-Hangzhou junction belt,together with the adjacent Shiwandashan foreland basin,Liuwandashan granite fault uplift,the Bobai-Cenxi structural zone,the Yunkai uplift,and the northern extension of the Luoding-Guangning structural zone（Yuexi thrust nappe structure）,the Yuexi fault uplift,and the Luoding basin,constitute the main body of the southeastern Guangxi Indosinian intraplate（orogenic）tectonic belt in southwestern South China block,while the eastern extension part of Yangtze block can reach the west of Daming Mountain-Dayao Mountains uplift,the western extension of the Cathaysian plate can reach the southeast of Yunkai uplift and the east of Luoding basin.（4）The coupling mechanism of the deep and the shallow structure in Lingshan segment of Qinzhou-Lingshan structural zone reveals that:The vertical-intersection coupling mechanism of deep shallow structure in Lingshan segment of Qinzhou-Lingshan structural zone is a direct reflection of the Mesozoic oblique amalgamation-intraplate orogeny of the structural zone.