Geochronology And Geochemistry Of Mesozoic Magmatic Rocks In Xibencha Area Of Dunhua Jilin Province

This paper takes mesozoic magmatic rock in Xibeicha Area Dunhua Jilin as object of study,through geochemistry study for LA-ICP-MS U-Pb chronology of zircon in magmatic rock and bulk element and microelement in magmatic rock,determines the formation age of magmatic rock in research area,and discuss the rock association of magmatic rock with different age in research area and its structural setting for formation.In the end,combining with regional geological data,discuss the Mesozoic regional structure evolution history in the research area.Xibeicha area is located in Emu town Dunhua Jilin,the geotectonic classification belongs to Siberian plate?I?,Xingmeng Paleozoic orogenic belt??-8?,compound orogenic subzone in southern margin of Song Jiaxing combined block??-8₄?,and the southern margin of Taton-Huangsong Neoproterozoic vestigital tectonic slice??-8₄¹?.The magmatic rocks are developed in the area,the outcropped area accounts for above70%of total area,the main rock type is granite.In the research area,the zircon in Mesozoic magmatic rock is automorphic-hypautomorphic,and has typical features of magma oscillatory growth zone.Datable results show that in the research area,Mesozoic magmatism can be further divided into two periods,late Triassic epoch?218²13Ma?and early Jurassic?188¹85 Ma?.According to total analysis results for rock,two intrusive units are located in the crossed line of granite?Gr?,Granodiorite?Gd?and trondhjemite?Tr?respectively,and the chemical feature of rock has obvious difference.According to rock identification results,observe the structure and tectonics of the rock combining with naked eye and microscope,and name the rock further.The base types of the rock in rock unit of late Triassic epoch granitic pluton are:syenogranite and monzonitic granite,and the representative rocks are biotite adamellite,biotite syenogranite etc.The base types of the rock in rock unit of early Jurassic granitic pluton are granodiorite,and the representative rocks are biotite granodiorite.In late Triassic epoch?218²13Ma?,the magmatism mainly consists of high potassium calcium alkali magmatic rock combination,the corresponding tectonic evolution history events:last phase of neopaleozoic–early Mesozoic,tectonic events of collision and suturing between Erguna-Xing'an-Songnen-Kiamusze blocks and North China Blocks,in the later period of geotectonics evolution,the transformation phase of structural constitution from extruded environment to stretched environment;In early Jurassic?188¹85 Ma?,the granodiorite was formed in plate subducting environment,island arc granite occurred before the collision,which was a part of plate tectonics.The corresponding tectonic evolution history events:early-middle Jurassic pacific plate dived into Eurasia,the subduction and extrusion in early Jurassic made the lithosphere thicken,magma underplating,and formed calcium alkali granite zone at leading edge of the plate.