Geochronology,Geochemistry And Tectonic Setting Of Intermediate-basic Intrusive Rock(Vein) In Keyouzhongqi Area Of Great Xing'an Range

The research area is located in the typical tin-tungsten-copper-lead-zinc-silver polymetallic metallogenic belt in the middle and southern part of the Great Xing'an Range,in which there are widely distributed intermediate-basic intrusive rocks,especially diorite porphyrite(containing fine crystal diorite)dikes and veins,These vein rocks are mostly along the NE,NNE-trending fault and penetrate,a few are NW and nearly NS-trending distribution,the scale is not large,generally only a few meters wide,about tens of meters to hundreds of meters long.Most of them cut through the Late Jurassic to Early Cretaceous volcanic strata,indicating that their age should belong to the Early Cretaceous and later,and is the product of the late Yanshanmovement.On the basis of regional geological survey,it is ascertains the spatial occurrence state of intrusive rocks in the study area and the contact relationship between intrusive rocks and surrounding rocks,determines the rock types of intrusive rocks.Through the analysis and study of the chronology and geochemistry of the intermediate basic intrusive rocks,the origin and tectonic setting of the intrusive rocks are discussed.The understanding not only complements the tectono-magmatic evolution of the Xingmeng-Mongolia orogenic belt,but also has certain significance for the exploration of copper and other metallic deposits related to theintermediate-basic rocks.(1)The lithology of the Early Cretaceous intermediate-basic intrusive rocks in the research area is mainly diabase,diabase porphyrite,diorite,diorite porphyrite and quartz diorite,most of them are produced in the form of dikes and veins,in which the veins are controlled by NE,NNE-trending and NW-trending faults and extend in type of?z?in space,it is shows the characteristics of tension fault control.(2)LA-ICP-MSZircon U-Pb and K-Ar dating results indicate that the intermediate-basic intrusive rocks in the research area were formed in the Early Cretaceous.It has the characteristics of multi-phase activities,and shows that the rocks change with the time and become more basic.(3)The intermediate basic intrusive rocks in the research area is characterized bylow Si O₂,high Al₂O₃ and Na₂O/K₂O,and weak or no negative Eu,it is enrichment of LREE and depletion of HREE.These geochemical characteristics may inherit the characteristics of the magma source area and indicate the properties of arc magmatic rocks.The whole rock geochemistry and zircon Hf isotopic characteristics reveal that the source area is mainly derived from the remelting of basic lower crustal materials,and has the characteristics of mantle-derived and crust-mantle magmatic mixing.(4)The intermediate-basic intrusive rocks in the research area were formed in the extensional tectonic setting of the Early Cretaceous,which is related to the closed collision of the Mongolian Okhotsk Ocean,it is the result of the bottom invasion of the Delaminationmantle-derived magma of the thickened continental crust after the closed collision of the Mongolian Okhotsk Ocean.