Geochronology,Geochemistry And Tectonic Significance Of Late Paleozoic Intrusive Rocks In Jingxia Area,Hami,Xinjiang

The study area is situated at the junction of the eastern Junggar orogenic belt and the northeastern Tianshan orogenic belt,showing a variety of complex structural features.It is adjacent to the multi-stage composite continental margin magmatic arc in the South and the Kanggur-Kushui suture zone in the north.In recent years,there has been much controversy about the collision time of the Zhongtianshan Mountains.The narrow Zhongtianshan Mountains is held between the two oceans and accepts the subduction of the two oceans at the same time.The dynamic conditions are complex,changeable and strong,the products of magmatic activity in the study area with continental margin arc background may represent the activity records of the Middle Tianshan Block,so it is important to take the intrusive rocks in Jingxia area as the research object to solve the problem of collision orogenic evolution and transformation of the Zhongtianshan Mountains.Based on the research results of predecessors in the eastern Tianshan Mountains,the magmatic evolution,genesis and tectonic environment of the intrusive rocks in Jingxia area are discussed through the analysis and study of lithofacies,chronology and geochemical characteristics.The late Paleozoic tectonic evolution history of Jingxia area in the Middle Tianshan Mountains is mainly discussed,which provides the time basis for the collision activities of the Middle Tianshan Mountains and is of great significance for the correct understanding of the tectonic evolution process in the East Tianshan Mountains.Late Paleozoic intrusive rocks in Jingxia area include Late Carboniferous intrusive rocks and Early Permian intrusive rocks.Late Carboniferous intrusive rocks mainly occur in the south of the Achikkuduk fault,mainly composed of granodiorite,monzogranite,granite porphyry,quartz diorite and diorite.Based on LA-ICP-MS zircon U-Pb dating,the diagenetic age of Carboniferous biotite monzonitic granite is(309.4 +2.2 Ma),which was formed in the Late Carboniferous.Early Permian intrusive rocks are mainly composed of diorite,quartz diorite,granodiorite,diorite porphyry,granite,monzogranite,potassium feldspar granite and granite porphyry.They are exposed in the form of small-scale bedrock and rock series,and their surrounding rocks are Lower Carboniferous Yamansu Formation and Upper Carboniferous Tugutubulak Formation,The diagenetic age of the weakly altered granite porphyry(295.1±5.4 Ma)and the granite porphyry(293.6±1.5 Ma)in the Permian are identified,which were formed in the Early Permian.Late Carboniferous granites and diorites show the geochemical characteristics of subduction type I granites,which were formed in the continental margin island arc environment.Early Permian diorites show the geochemical characteristics of crust-mantle mixed source I-type granites.Early Permian granite porphyries show the geochemical characteristics of crust-derived remelted S-type granites,which were formed in island arc-collision environment.The reaction of island arc to collision orogeny lags behind.The contact collision between the two edge systems may begin at the end of Late Carboniferous,and the early Permian is its collision orogeny stage.The Middle Permian collision orogeny ends and enters the period of debris and subsidence.