The Mesozoic Structural Deformation And Evolution Around The Yangtze Block

There are some Paleo-Tethys sutures around the Yangtze block, such as the Jinshajiang-Ailaoshan suture, Changning-Menglian suture and Ganzi-Litang suture at its southwest margin, and the Animaqin-Mianlue suture at its north margin. We have known the evolution of the progress of open-expand-subduction-close for Paleo-tethys. This paper mainly studied the deformation, sedimentary structure and related tectonic chorology at the northern and western Yangtze block and neighbouring area, and discussed the particular progress from continental collision to intra-continental deformation in the Tectonic belt around Yangtze block.We have known that the margin of Yangtze block has experienced the compression shortening deformation in early-Mesozoic, this deformation is related to the subduction and collision of the Paleo-Tethys ocean in this time. The collision at the northern Yangtze block is in early-mid Triassic, the Mianlue suture has experienced intense obduction-nappe structure from north to south in the early collision period, and formed imbricate thrust structural framework related. After the dominated collisional deformation, the northern Yangtze block and neighbouring orogen superimposed intense ductile and brittle slip deformation. The Ar-Ar age of the muscovite is 223 Ma in the mylonitzed green-schist experienced sinistral ductile deformation in Mianlue suture. This age consistents with the age of the granite changed to the extending environment in late-Triassic in south Qinling orogen, and indicate that the northern Yangtze block has turn into the intra-continental deformation in late-Triassic, and the deformation changing mode is lateral slip displacement along the orogenic belt. At late-Mesozoic, there are two important ductile and ductile-brittle slip shear deformation belts in south Qinling tectonic belt, named the Ningshan sinistral slip fault and Ankang dextral slip fault. The 40Ar-39Ar dating (160-173 Ma) of the syn-deformation mineral and ziron dating (186 Ma) of the granite intruded in the deformationed rock indicate the deformation time is early-mid Jurassic. The different kinematics direction indicate the tectonic effect of the south Qinling belt in early-mid Jurassic is lateral extrusion to east along the orogenic belt.he Cenozoic sinistral slip structure obviously destroyed the Mesozoic deformation framework of western Yangtze block and neighbouring area along the Longmenshan, Anninghe and Jinshajiang, so the collisional related deformation before Cenozoic around the Yangtze block is difficult to recognize. In the complex Cenozoic deformation framework, this paper discovery the development of the Mesozoic basins is related to the forming of the NW-NNW strick slip faults depend on the sedimentary character and paleo-current direction. This left-lateral slip tectonic belt must be the tectonic response for the collision in Qinling belt and Ganzi-Litang belt in western Yangtze block, and the deformation time is late-Triassic. Meanwhile, the thrust and fold thicking structure from west to east in the Songpa-Ganzi terrain is also in late-Triassic. The scrapes on the slip faults indicate that exist thrust deformation from SW to NE before the slip deformation, and the time is difficult to limit because there are no mata-deformation mineral and magma. Depended on the relationship between the faults and the basins and the tectonic sstting, we consider the thrust deformation should develope in late-Mesozoic to early-Jurassic. The sinistral shear deformation time must begin in late-Triassic and continued to Jurassic basing the strata character study of the Ganluo and Jiuxiang basins. And the displacement of slip at western Yangtze block reaches to 27 km at least by preliminary estimate.The Paleo-Geomagnetism research has evident that the Yangtze block has clockwise rotated about 30°, and there are a serious sinistral slip faults around the Yangtze block may related to the rotation, such as Longmenshan fault, Anninghe fault, Ziluo fault, Huayinshan fault, and etc. The north margin of Yangtze block is complex because of relating to collision-accretion of the Chinese continents. After the tethys ocean closed, the collision phase is dominated by the high-angle thrust vertical to orogen firstly, and formed the imbricate stow thrust-nappe framework. Then the collision quickly switches to intra-continental deformation with slip displacement or lateral extrusion along the orogen, and superimposing the sinitral slip deformation caused by the clockwise rotation of the Yangtze block at the same time. So the Mesozoic deformation around the Yangtze block shows a special continental collision process in the Paleo-Tethys field, which is the Yangtze block south of the collisional belt rotated clockwise with north direction subduction-collision.