Jurassic Structural Deformation Features Of Zhamunian-Gesang,Tibet And Its Significance

Located in the northern part of the Tibet Plateau,Qiangtang is located at the collision and binding site between Gondwana and Eurasia.It is sandwiched between the Bangong-Nujiang Suture Zone and the Jinshajiang Suture Zone.It is a key areas about geoscientific field study with the ancient Tethys Ocean subduction and The two continent collides.The study of the geological evolution history of Tethys has been a hot topic in geosciences.Foreign scholars have conducted in-depth studies on Tethys tectonic evolution based on the classical theory and model of plate tectonics and collisional orogeny theory,but some phenomena are difficult to explain with the perspective of petrology.For example,island arc magmatic belts are found on both sides of the suture zone.This paper,based on the perspective of structural analysis theory,relying on the 1:50000 regional geological survey project,by carrying out large-scale mapping in the field,and constructing measured profiles of important strata,the tectonic patterns and deformation periods of the Jurassic strata in the study area are studied.Preliminary research shows:A three-stage compound fold of the Sewa Formation in the south of the Rongma Tibet,followed by a period of gentle-open folds.The direction of the early fold is mostly east-west direction,and the trend of the cleavage that development between the fold wing and the center of the hinge is similar to the east-west direction.It is formed by the north-south compression.In the region of Renacuo,the Early Cretaceous Meiriqiecuo group and the underlying strata of the Jurassic Sewa Formation are angular unconformity contact relationships,and the Sewa group‘s closed folds.superimposed folds,and other structures appear in remote sensing images.The style is not reflected in the Volcanic Rocks of Meiriqiecuo,and it can be inferred that the age of the deformation of the Sewa Formation was at least before the Early Cretaceous.In combination with the tectonic setting of the South Qiangtang Basin,it was inferred that the three-stage compound folds of the Sewa Formation in the study area are the products of the subduction of the Bangong-Nujiang Ocean to the north,and the superimposed flat-open folds may be related to the southern Qiangtang block with the Lhasa block collision.In addition,the deformation sequence of the Jurassic Shaqiaomu Formation in the study area was studied by measuring the lithologic structural section.Comprehensive studies have shown that the Jurassic shaqiaomu formation has developed two stages of structural deformation in the study area,and the Nansha Qiaomu Formation and Rongwow Formation in Rongma Township have similar deformation characteristics.The first-stage tectonic stress is mainly the north-south compressional stress and is accompanied by a certain amount of left-hand shear.The second phase of the coaxial progressive deformation,the formation of E-W upright folds.By studying the ductile shear zone,the differential stress of the ductile shear zone is between 63.02MPa and 84.15MPa,and the strain rate is between5.62×10^-13s^-1-2.76×10^-12s^-1.