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LA-ICP-MS Zircon U-Pb Dating for K-feldspar Granites in Lianghe Region,Western Yunnan and Its Geological Significance

XIE Tao1,LIN Shiliang1,CONG Feng1,LI Zaihui1,ZOU Guangfu1,LI Junmin1 and LIANG Ting2(1.Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China;2.State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,Hubei,China)  
CL imaging,LA-ICP-MS U-Pb dating and trace element analysis were carried out for the zircons from two representative K-feldspar granites in the Lianghe region,western Yunnan.The results show that the zircons display oscillatory zoning which suggests a magmatic origin.Zircons from two samples show similar REE patterns,which are high in Th,U,and REE,relative enrichment of HREE,and significant Ce positive anomalies and Eu negative anomalies.These are the characteristics of magmatic zircon of crustal origin.The weighted average 206Pb/238U ages for zircons from two samples are(60.7±0.6)Ma and(115.8±1.0)Ma,respectively,which show that the granites were formed in Paleocene and Early Cretaceous.Combined with regional geology,the multi-phases of magmatism in the Tengchong block took place in the late Mesozoic-early Cenozoic,which may be considered as magmatism response to the Tethys evolution in the Sanjiang region,western Yunnan.This offers constraints on the geological evolution in the eastern edge of Qinghai-Tibet plateau.
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