Magmatic Activity And Tectonic Setting Of Basin Formation From Late Carboniferous To Permian In Santanghu Area,NE Xinjiang

The Santanghu area,NE Xinjiang are located in East Junggar.Volcanic rocks of Late Carboniferous-Permian are well exposed in the Santanghu basin and its adjacent area,which offers an excellent opportunity to understand the tectonic evolution of East Junggar during the Late Paleozoic.Based on a combination of the outcrop,seismic profile and drilling-core data,this paper made an detailed analysis of Late Carboniferous-Permian stratigraphic framework,distribution and rock assemblage,tectonic evolution and the Basin nature in Santanghu Basin and adjacent area by means of isotope chronology,petrology,mineralogy geochemistry and isotope geochemistry.?1?Harjiawu Fm.and Kalangang Fm.in the Upper Carboniferous are contemporaneous heterotopic facies,which covered on the Batamayineishan Fm.with angular unconformity.The four stratum of Wulabo Fm.,Jingjingzigou Fm.,the Lucaogou Fm.,and Tiaohu Fm.in Middle Permian are integrated contacts.?2?Volcanic rocks of Late Carboniferous well develop in Santanghu Basin and adjacent area,which contain basic-intermediate volcanic lavas and pyroclastic rocks.Volcanic rocks of Late Carboniferous are sodium calcium alkaline.They are enriched in LILE?Ba,U,Sr?and LREEs,with depletion of Nb,Ta and Ti.The samples have lower the initial ratio of Sr isotope and positive?_Nd?t?,which indicate the depleted mantle sources.High Nb/Th and Nb/U ratios show the sources metasomatized by subduction plate melt.Combined with regional geological background,Volcanic rocks of Late Carboniferous in Santanghu area was the product of partial melting of lithospheric mantle material and slab breakoff as an important geodynamic process accounts for the post-collisional magmatism.?3?Geochemical characteristics of Basalt and mafic dikes in Permian from Santanghu Basin and its adjacent area are with high Total-alkai?Na₂O+K₂O?,TiO₂ and Al₂O₃,low MgO and FeO,while olivine diabase and diabase are sodium calcium alkaline.They are enriched in LILE?Ba,Pb,Sr?and LREEs,with depletion of Nb,Ta and Ti.High TiO₂?Nb?Zr/Y show the intercontinental Basalt.In addition,they are plot in the area of intracontinental Basalt on the discrimination diagram.In association with regional deformation investigation,we suggest the Permian of Santanghu area is an intracontinental extensional background.Based on the timing of opening and closing of ocean and stratigraphic filling characteristics of basins,It is believed that the Santanghu Basin has undergone four evolutionary stages and corresponding basins as follows:?1?Ordovician-early devonian:Santanghu area is passive continental edge;?2?Middle-Devonian to Early Carboniferous:Santanghu area is the active continental margin of the Siberian craton;?3?late Carboniferous-early period of Early Permian?320Ma²90Ma?:Santanghu area is post-collisional extension rift?4?Late period of early Permian-Middle Permian?280Ma²60Ma?:Santanghu area is intraplate extension rift.