Geological Characteristics And Tectonic Significance Of Kangur-Kushui Tectonic Mixed Belt In Eastern Tianshan,Xinjiang

The East Tianshan Orogenic Belt in Xinjiang is located between the southern margin of the Eastern Junggar Orogenic System and the northern margin of the North Tianshan Orogenic System.It is a key area for the convergence of ancient plates and the accumulation of crustal collages.In recent years,domestic and foreign scholars have been Geological issues such as the closure time limit of the Tianshan Ocean are controversial.The Kanggur-Kushui structural mixed rock zone,as a product of the subduction and proliferation of the ancient Tianshan Ocean to the mainland,retains extremely important structural tracks,which provides an important basis for inferring the ancient Tianshan Ocean tectonic evolution and environment.This thesis takes the middle and basic rock assemblages in the Kanggur-Kushui structural mixed rock belt in East Tianshan as the research object.Through detailed field geological work and indoor petrography,zircon chronology and geochemistry,as well as A large number of predecessors,such as chronology,geochemistry,and petrography,have collated and summarized the data to reveal the origin of the Kangguer-Kushui structural mixed rock belt and its tectonic evolution process and tectonic environment.The conclusions and understandings obtained are as follows.(1)The matrix of the Kanggur-Kushui structural mixed rock zone is mainly a set of marine fine clastic rocks in the Upper Carboniferous Wutongwozi Formation;the rock blocks mainly include radiolarian-bearing siliceous rocks,altered basalt and weak erosion Combination of fine-grained angle diorite and strongly altered diabase.Among them,the radiolarian-bearing siliceous rocks are products of oceanic sediments;diabase and basalt are lower-upper oceanic crust fragments,reflecting a set of rock assemblage characteristics alternately between the deep-sea plain-submarine fan depositional environment and submarine volcanic eruptions.(2)The LA-ICP-MS zircon U-Pb method was used to determine the isotope age of the gabbro blocks in the Kanggur-Kushui structural mixed rock belt in the Yamansu area is 336.3 ± 2.3Ma;In the basalt series,the large ion philophile elements are depleted,and the high field strength elements are enriched.The rare earth distribution pattern shows micro-enrichment characteristics of light rare earths.The rocks are formed in the island arc environment,which is the direction of the Kanggur Ocean during the Early Carboniferous.The product of two-way subduction of the Junggar-Kazakhstan plate in the north and the Zhongtianshan block in the south.The isotopic age of the diorite porphyry rocks obtained in this work is 295.1 ± 5.4 Ma,and the neutral rock assemblages are mainly calcium-alkaline series,showing a consistent right-inclined light rare earth enrichment in the rare earth distribution pattern diagram,indicating that this type of rock Formed in the environment inside the plate,it is the product of the collision and extension phase in the plate after the Kanggur ocean basin is closed.(3)The diagenetic age and tectonic environment of basic and neutral rocks during the Early Carboniferous-Early Permian in the comprehensive comparison study area.In the Early Carboniferous(336.3 ± 2.3Ma),most of the basic rocks in this area have the characteristics of an island arc environment,indicating that the Kanggur Ocean was still in the subduction stage during this period,and was neutral in the Early Permian(295.1± 5.4Ma)study area.The rock has the characteristics of the internal environment of the plate,indicating that the Kanggur Ocean has been completely closed and has transformed from the subduction stage to the intraplate evolution stage.