Kalaqin Complex Batholiths Geochronology,Geochemistry And Tectonic Evolution

Inner Mongolia Kalaqing complex batholiths located at northern margin of the North China Craton,north of Xingmeng orogenic belt,south of Yanshan orogenic belt.With Kalaqin complex batholith as the research object in this paper,based on a detailed geological survey and high-precision geochronology,divided different stages of magmatic activities during Late Paleozoic to Mesozoic,and established magmatite chronological framework of Kalaqin complex batholiths.Combined with petrography,geochemistry,systematic research of isotope data of Kalaqin complex batholiths,discussed property of source region magmatite and tectonic evolution during Late Paleozoic to Mesozoic.During late Paleozoic to the batholiths experience for at least six period magmatism:Late Carboniferous-Early Permian,Middle-Late Permian,Early-middle Triassic,Late Triassic,Jurassic and Early Cretaceous.Rock in late Carboniferous-early Permian without negative Eu-anomaly,high Sr and low Yb,Nb,Ta negative anomalies,Show Features of magmatic rocks in subduction zone,middle-late Permian rock in the presence of moderate negative Eu-anomaly,low Sr low Yb,Crustal thickening began early in the Triassic,and positive Eu-anomaly are present in rocks,early-middle Triassic rock are present positive Eu-anomaly,from early to late granite display changes from high Sr and low Yb to low Sr and low Yb,crustal reached to the thickest level and began to Thinning,late Triassic rock show strong negative Eu-anomaly,low Sr and high Yb,show the situation of continuous thinning of the crust.Jurassic rock exist moderate negative Eu-anomaly,low Sr and high Yb in early stage,low Sr and low Yb in late stage,early Cretaceous rock without negative Eu anomaly,high Sr and low Yb,the crust began to thicken again.Late Carboniferous-Early Permian stage,the area turn into continental margin arc environment;magmatite that characterized by collision orogenic environment in 270Ma,which represent the end of continental margin arc environment and the begin of collision orogenic environment,overthrust structure found in sourthern of Kalaqin in 270-260Ma,proves this time Kalaqin complex batholith located in collisional environment,and in 260-250Ma,magmatic activity shows the characteristics of post-collsional tectonic setting,Early-middle Triassic the environment turn to post-orogenic type,A-type granites outcropping in Late Triassic further evidence that in about 220Ma,this area turn into post-orogenic extensional environment,in Jurassic(192-150Ma)period,the formation of continental collision-type granites and a series of overthrust tectonic south of Yanshan orogenic belt indicated that this time the area turn into extrusion environment,in early Cretaceous(141-122Ma)period,the tectonic line shift from the NE to NW,and still in the extrusion environment.