Paleozoic Structural Deformation And Evolution Of The Qinling Group

The Qinling orogenic belt,as a tectonic amalgamation belt of South and North China paltes,has been concerned by geologists for a long time.The Qinling Group is located in the core of Qinling orogenic belt,adjacent to the main suture zone of two plates-Shangdan suture zone,which is one of the oldest and most deformed geological units in the Qinling orogenic belt.Its strong tectonic deformation records abundant geological information in the convergence process of the two plates,which is of great significance for inversion of the convergence process of the two plates.In this paper,the structural geology,geochronology and geochemistry of the basement and granites of the Qinling Group are studied,and the Paleozoic evolution process and dynamic background of the Qinling Group are discussed.?1?Field investigation,combined with microstructure deformation analysis of the basement the Qinling Group revealed that the structural deformation of the Qinling Group is characterized by the obliquely upward extrusion from east to west.The tectonic deformation temperature is 480?560?,the corresponding metamorphic facies is high greenschist facies to low amphibolite facies,the differential stress is20.19?56.54MPa,the strain rate is 1.82281*10^-13?5.62102*10^-13s^-1,the Fulin parameter is 0.29?0.47,and the vorticity value is 0.57?0.75.?2?The structural deformation,chronology and geochemistry were used to study the Piaochi granites in the north,the Jiedaogou granites in the core and the Shangnan granites in the south of the Qinling Group.The Piaochi granite was formed in506±18Ma by the partial melting of ultra-high metamorphic rocks exhumation into the lower and middle crust.It was influenced by the Zhuxia fault zone with characterized of a high angle of foliation and low angle of lineation.The Jiedaogou granite has a similar structural deformation with the basement of the Qinling Group,with the characteristics of obliquely upward extrusion from east to west.The Jiedaogou granites was formed in the 426±5.8Ma by partial melting of a thickened lower crust caused by the collision between the South and North Qinling terrane.The vein cutting through the Jiadaogou granite yield 395.7±7.4Ma constrained the upper limit of deformation age.The Shangnan granite was formed at 422.1±5.9 Ma by partial melting of a thickened lower crust of the Qinling Group.Due to it is close to the Shangdan suture zone,its structural deformation mainly shows the characteristics of sinistral shear movement of the Shangdan suture zone.Based on the analysis of the regional geological background,the Paleo-Qinling ocean began to subduct from 514Ma.Under the background of the collision between Yangtze and North China plate,the Qinling Group thickens and experienced obliquely upward extrusion from east to west during 426±5.8Ma?395.7±7.4Ma.At about320Ma,the continuous compression after the closure of the two plates led to the left strike-slip movement of the Shangdan fault belt,and the southern part of the Qinling Group was involved in this shear activity.