Geochronology and geochemical characteristics of the Bozhushan granite in the southeastern Yunnan and its geological significances
The W-Sn-Pb-Zn polymetallic deposits in the Bozhushan area of Southeastern Yunnan are closely and genetically related to the large Bozhushan granite complex.Whole-rock geochemistry,zircon U-Pb dating and Hf isotope analysis have been carried out to investigate the emplacement age,petrogenesis and formation background of the granite complex.Two stages of granites have been identified in the granite complex.The LA-ICP-MS zircon U-Pb ages of the late granite range from(87.08±0.55)Ma to(87.29±0.69)Ma.All granites are characterized with high contents of SiO2(63.37％～72.07％)and K2O(4.96％～6.19％),low contents of Fe and Mg,A/CNK values ranging from 1.03 to 2.42,obviously differentiated light and heavy rare earth elements(LREE/HREE=14.0～26.5),obviously negative Eu anomalies(δEu=0.38～0.62),enriched large ion lithophile elements including Rb,Th and U and rare earth elements including La,Ce,and Nd,and depleted Ba,Ta,Nb,Sr,Y and Yb.Their zircons haveεHf(t)values ranging from-9.31 to-5.14.They have geochemical and isotopic characteristics of the high potassium-calcium alkaline peraluminous S-type granite.Their second-stage granite model ages(tDM2)are ranged from 1476 Ma to 1737 Ma,indicating that their magmas could be derived from the partial melting of Early and Middle Proterozoic lower crust materials.The comprehensive research suggests that the Bozhushan granite complex was formed by magmas derived from the partial melting of the Early and Middle Proterozoic lower crustal materials due to the upwelling of the asthenospheric mantle under the extensional setting in the Cretaceous.
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