Geochronology And Geochemistry Of Jurassic Granitoids In Sijiazi-jinchanggou Region,aohan Banner,Inner Mongolia

The research area is located in Aohanqi,Chifeng City,Inner Mongolia-Chaoyang City,Liaoning Province,which is tectonically situated within the northern margin of the North China Craton,belonging to the binding site of the Xingmeng orogenic belt and the North China Craton.The Mesozoic intrusive rocks of the study region consist part of the western Liaoning magma zone,which also belong to the central part of the circle-Pacific large volcanic belt and east part of the Great Xing'an Range-Yanshan volcanic belt.We undertook zircon U–Pb dating and geochemical analyses?major and trace elements?of the Jurassic granitoids from Sijiazi-Jinchanggou region,Aohan Banner,Inner Mongolia,with an aim to determine their age,petrogenesis and sources,which is important for understanding the Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt.Through the field geological survey,it is found that five Jurassic granitic plutons exist in the study area,i.e.,the Laoniuwo,Loushang,Yujiayingzi,Beiniuxihe,and Jiangshangou plutons,respectively.The rock association is mainly composed of monzogranite,granodiorite and alkali feldspar granite.The zircons from two granitoid samples are euhedral–subhedral in shape,display fine-scale oscillatory growth zoning and have high Th/U ratios,indicating a magmatic origin.The results of LA–ICP–MS zircon U–Pb dating indicate that the granitoids from Sijiazi-Jinchanggou region,Aohan Banner,Inner Mongolia formed during the Jurassic time,with the ages of192±2 Ma and 150±1 Ma,respectively.Geochemical data show that these Jurassic granitoids belong to high–K calc–alkaline series,and are characterized by high SiO₂,high Na₂O+K₂O,low MgO,low total Fe₂O₃,and low CaO.Moreover,they are enriched in large ion lithophile elements and light rare earth elements,and depleted in high field strength elements and heavy rare earth elements.Petrological and geochemical characteristics of these Jurassic granitoids suggest that they are all I-type granitoids,and their parental magmas were likely derived from the partial melting of lower crustal materials.These data,combined with previous studies on the contemporaneous magma-tectonic activities in NE China,suggest that the generation of the Jurassic granitoids from Sijiazi-Jinchanggou region,Aohan Banner,Inner Mongolia was related to the subduction of Paleo-Pacific plate.