Research On The Sibao Ductile Shear Zone, Northernguangxi

The sibao area of northern Guangxi, is located beween the Yangtze and Cathaysian blocks, which is an important window to reveal the tectonic history of South China. Previous studies concentrate on sedimentology, geochronology and isotope geochemistry of the Neoproterzoic strata or magamatite. However, The study on the Caledonian ducticle deformation has not been given enough attention. Therefore, based on the previous research, this thesis aims to investigate its formation mechanism and significance of the Sibao ductile shear zone by integrating field observation, microstruture, magnetic fabric,X-ray petrofabric and geochronlogical analyses. The main research contents and results are summarized as follows:1. Discovery and determination of the Sibao ductile zone, northern GuangxiThe Sibao area has typical macroscopical characteristics involving intensive penetrative foliation, stretching lineation, A type folds and fine-grained dynamic metamorphic rocks. Based on the magnetic fabric of tectonites, a Sinistral transpression ducticle shear zone trending in NE30°(inclination SE120°,dip 40°) in the Sibao area of northern Guangxi is recognized. Anisotropy of magnetic susceptibility(AMS) indicates that the Sibao ductile shear belt is 10 km wide and more than 30 km long, which consists of a strong strain zone about 4 km and weak strain zones. The hanging wall napped to 356°N with a low angle of 20~30°.2. Deformation age of the sibao ductile zone, northern GuangxiThe new dynamic metamorphic mineral illite has 40Ar-39 Ar and Rb-Sr isotope ages of 393.2~419.4Ma. This age represents the tectonic deformation time of the sibao ductile shear zone.3. The formation and obique collision of the sibao ductile zone, northern GuangxiThe rift between the Yangtze block and Cathaysia block was gradually closed in the late Caledonian. The sinistral transpression ductile shear zone was formed due to the force at the margin of the Yangtze blok when the Cathaysia block obliqe subducted from SSE176° to the Yangtze block. The obique thrust direction and angle of the Cathaysia block was estimated.In conclusion, this thesis systematically investigated the ductile deformation of the sibao area, northern Guangxi. Field observation, microstuctual observation, magnetic fabric and X-ray test and analysis were conducted to identify the scale, attitude, movement mode, mechanical properties and strain evolution of the sibao ductile zone. The geochronological analyses determined the time of the tectonic deformation of the sibao ductile zone.The mechanism and direction of the movement between Yangtze block and Cathaysia block during the Guangxi movement. The results provide reliable data and information for exploring the evolution and dynamics of intraplate orogenic process.