Genesis And Formation Mechanism Of Neoarchean Potassic Granites In Benxi Area,Liaodong

The study area is located in the northeastern part of the eastern North China Craton,which is an important Archean evolution area in the study area.Neoarchean potassic granites are widely developed in this area,potassic granites play an important role in exploring the formation and evolution of the early continental crust of the North China Craton.In this paper,the petrology,geochemistry and SHRIMP zircon U-Pb isotope chronology of Liujiapuzi pluton and Majiagou pluton in Benxi area are studied,the formation age,genetic type,provenance properties and tectonic environment of the potassic granites in this period are revealed.The Liujiapuzi pluton is porphyritic fine medium-grained biotite monzogranite,it belonged to the potassium rock series of quasi-aluminum-weak peraluminous and high potassium calc-alkaline;it mainly enriched high field strength elements La,Th and large ion lithophile elements Sr;deficit P element,high field strength element Nb;REE curve is right inclined with negative Eu anomaly,belong to type I granite.Dating data show that the ziron U-Pb age of the rock mass is 2518±21Ma,which was formed in the late Neoarchean;magma mainly comes from the crust,is the product of the mixing of crust-derived and mantle-derived magma,the pluton was formed in an active continental margin island arc environment associated with subduction.The Majiagou pluton is gneissic medium-fine biotite monzogranite,it is a potassic rock of weak peraluminous and high potassic calc-alkaline series;mainly enriched in high field strength elements La,Zr,Th and large ion lithophile elements K,Nd,deficit P element,high field strength elements Nb,Ti and large ion lithophile elements Sr;REE curve is right inclined,negative Eu anomaly,it belongs to S-type granite.Zircon U-Pb dating show that the ²⁰⁷Pb/²⁰⁶Pb weighted average age is 2490±21Ma,formed in the late Neoarchean.Magma comes mainly from the earth’s crust,it is the product of partial melting of metamorphic mudstone,formed in extensional environment after collision and orogeny.Combined with the structural evolution of Benxi area in eastern Liaodong and the analysis of previous research data,in the late Neoarchean period（2518±21Ma）,the Longgang and Wollin landmasses of the eastern block of the North China Craton were not yet integrated,the Liujiapuzi pluton is the product of oceanic subduction to the continent,the magmatic evolution process of the first subduction collage of the North China Craton microcontinent was formed together with the Majiagou rock mass（2490±21Ma）formed in the extensional environment after collision orogeny in the study area,It represents the last magmatic activity before the formation of the consolidated basement of the Archean craton in North China.Indicating that microlandmasses in Benxi area had been collaged in the late Neoarchean period,together with other regions to formed the stable Archean Craton of North China.The paper has 28 figures,9 tables and 119 references.