A Study On The Metamorphism And Deformation Of Sibao Group In The Yuanbaosban Area Of Guangxi

The NE-SW striking Jiangnan Orogen is located between Yangtze and Cathaysia blocks,while Yunbaoshan area belongs to its southwest exposure.The oldest exposed strata is Sibao group(>835 Ma)in Yuanbaoshan area,after experienced ~835-815 Ma intensive orogeny event,the Sibao group was intruded by 815 Ma Yuanbaoshan pluton.The Yuanbaoshan pluton and associated country rocks was uplifted to earth surface and unconformably overlain by Danzhou group(<800 Ma).All these old units were reconstructed by the Paleozoic intracontinental orogen and formed similar gneiss dome structure which cored by old strata and mantled by younger units.This dome records several phase deformations,hence it is important to research on tectonics evolution and intracontinental orogen of the south China block.In this study,we try to decipherer the Sibao group's sedimentary features,structural phase and metamorphism.Our works devoted to resolve the tectonic evolution from the Neoproterozoic to the Early Paleozoic,and as well the metamorphic process in the Yuanbaoshan region.After detailed field work,microscope analysis and detrital zircons analysis,we concluded that 1)the Sibao group deposited before 835 Ma,and 2)intruded by S-type Yuanbaoshan granite,and 3)then both Sibao group and Yuanbaoshan granite was unconformably overlain by Danzhou group during intracontinental extension.The finally intracontinental orogen uplifted all buried units and exposed them to earth surface by positive flower structures.Based on primaryThermocalc modeling results,the peak metamorphism of Paleozoic bury is about~700-750 ? and ~7-8Kbar.Combined our observation and regional studies,anintegrated intracontinental extension to intracontinental geological process was illustrated to us.