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Petrogenesis of the Gaofengshan granite in Gejiu area,Yunnan Province:Zircon U-Pb dating and geochemical constraints

The Gaofengshan granite is located in the eastern part of the Gejiu ore district,Yunnan Province.The lithology of the granitoid is mainly medium grained biotite monzonitic granite.In this paper,zircon U-Pb dating and geochemistry of the Gaofengshan granite is studied to constrain its geochronology and petrogenesis.Zircon LA-ICP-MS dating yields an emplacement age of 85.76±0.58Ma,which suggests that this granite formed in the Late Cretaceous.Geochemically,this granite is silica riched in composition, with high content of alkali(Na 2 O+K2 O).It’s a metaluminous to peraluminous granite and belongs to the high-K calc-alkaline series, and characterized by enrichment of Rb,U,Ta,Pb,Nd and depletion of Ba,Nb,Sr,P,Zr,Eu,Ti.The abundance of∑REE varies in the range of 146.7×10 -6 to 236.1×10 -6 ,and it has intensely negative Eu abnormality(δEu=0.03～0.11).What’s more,it reflects a tetrad-like effect with a shape of"M".These features are coincident with A2 granite.Geochemical characteristics show that the parental magma of the Gaofengshan granite was derived from the partial melting of crust,and experienced a strong crystal fractionation process.New data of this study indicate that the Gaofengshan granite was one component of the large scale Late Cretaceous magmatism in western Cathaysia block,which viewed as under a regional lithospheric extension tectonic setting.