Formation Age,Geochemical Characteristics And Tectonic Environment Of Granodiorite Porphyry Of Mesozoic From Baishan Areas,Jilin Province

The geographical location of Baishan,Jilin Province is 3km south of Baishan City,Jilin Province?Hunjiang District?,and the northern boundary is Banshi Town,9km north of Baishan City.The geotectonic location is located in the northeastern North China Craton.The Mesozoic crustal tectonic deformation in the study area is very strong and there is strong magmatic activity.The Mesozoic intrusions are stock,dike and dyke intrusion along the NE-trending major fault in the area.In this paper,the Xinlu and Tuodaogou granodiorite porphyry are studied,and petrography,chronology and petrochemistry are studied to determine the formation age and analyze the relationship between rock genesis and crustal tectonic deformation.To dicuss geotectionic evolution background based on the known data.The weighted average age of LA-ICP-MS zircon U-Pb in Xinlu and Tuodaogou granodiorite porphyry is 163.3±0.77Ma and 162.3±1.6Ma,which is the product of the magmatism in the same period.The formation time is late Jurassic.The geochemical analysis results show that the Xinlu and Tuodaogou granodiorite porphyry has high SiO₂?64.44%-67.29%?,Al₂O₃?16.29%-16.54%?,K₂O=?2.42%-2.87%?,and Na₂O?2.39%-4.83%?contents,low MgO?1.22%-1.78%?content,and A/CNK value of0.98-1.09.Enrichment of large ion lithophile elements such as Ba,Cs,K,etc.,loss of high field strength elements such as Nb,Ti,P.It is high Sr low Y,Sr/Y ratio of 47.9-57.0,La _N/Yb_N ratio of 9.99-19.18.The distribution pattern of rare earth elements is right-dip type,and the fractionation of light and heavy rare earth elements is obvious.The?Eu value is 0.93-1.18,which has a weak positive anomaly.It belongs to the quasi-aluminum-weak aluminous calcium-alkaline-high potassium calc-alkaline series Adak type I granite.The pluton formation caused the thickening of the continental crust due to the subduction of the Paleo-Pacific Plate to the North China Craton.According to the regional geological background and previous research results,this paper divides the tectonic evolution of the Mesozoic period into four stages in the Baishan area.During the Early Triassic to the Middle Triassic,the Yangtze Plate subducted into the North China Plate and caused the lower crust to thicken.After the Late Triassic to Early Jurassic,the ultrahigh-pressure metamorphic rocks formed after the collision between the Yangtze and North China Plates In the early stage of the Middle Jurassic-Early Cretaceous,the study area was in the subduction stage of the Paleo-Pacific Plate to the North China Plate.After entering the middle of the Early Cretaceous,the northeastern rocks of the North China Plate were demolition and thinning,and the study area was transformed into a stretching stage.