Characteristics And Geological Significance Of The Mid-triassic Granite Of Fudong Area In Jilin Province

The Fudong area,which is located in the eastern section of the northern margin of north China plate.During the period of Mesozoic is mainly influenced by the Paleo-Asian Ocean tectonic system and the Paleo-Pacific system.This article selects the two Triassic granitic intrusive mass as the research object,we carried on the detailed field geological investigation,through to the intrusion of zircon sample U-Pb chronology research,determine the formation of intrusion.Based on the study of the geochemical characteristics of the samples and the results of previous studies and regional geological history,this paper analyzes the genesis and tectonic background of rock formation in this period,and provides new geological data for the magma activity and tectonic evolution of the Triassic intrusive rocks in Yanbian Fudong area.In this paper,the lithological research objects of the Triassic intrusive rocks in the fudong area are mainly granite diorite and monzonitic granite.Among them,the U-Pb isotope age of zircon of granodiorite was 243.9±2.0Ma,indicating that it was formed in the middle Triassic.The U-Pb isotope age of the monzonitic granite is236.9±1.1Ma,which is also formed in the middle Triassic.The geochemical characteristics of the two intrusive rocks in the Fudong area are similar.They are characterized by high Si?66.68%⁷4.58%?,high alkali?K₂O+Na₂O=6.66%⁸.56%?,low magnesium?MgO=0.13%¹.64%?,low calcium?CaO=0.81%³.17%?,high aluminum?13.15%¹5.73%?,with A/CNK value of 0.98-1.10.The REE pattern curves are right-dipping with negative Eu anomalies and well LEE fractionation.Trace elements are characterized by loss Ba,Nb,Ta,while Th,Zr,Hf and Pb concentration are the characteristics.It was found that,in Harker diagram,the content of MgO,TiO₂,CaO,P₂O₅,FeOt,Al₂O₃ in the sample had a linear negative correlation with the content of Si O₂.The common occurrence of amphibolite in the sample,not including bauxite?white mica,garnet,etc.?,shows the characteristics of type I granite.The geochemical characteristics of the rocks combined with the related structural discrimination diagram indicate that the Triassic granite in the fucave area is formed by the partial melting of the crust material.Its formation may be related to the subduction collision of the Paleo-Asian ocean.