Qinghu zircon:A working reference for microbeam analysis of U-Pb age and Hf and O isotopes  

作　　者：LI XianHua TANG GuoQiang GONG Bing YANG YueHeng HOU KeJun HU ZhaoChu LI QiuLi LIU Yu LI WuXian 

机构地区：[1]State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences [2]CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China [3]Institute of Mineral Resources, Chinese Academy of Geological Sciences [4]State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences [5]State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences

出　　处：《Chinese Science Bulletin》2013年第36期4647-4654,共8页

基　　金：supported by the State Key Laboratory of Lithospheric Evolution and the Ministry of Science and Technology of China(2007AA06Z126)

摘　　要：Zircon is the most useful mineral for studies in U-Pb geochronology and Hf and O isotope geochemistry.Matrix effect is a major problem of the microbeam techniques such as SIMS and LA-(MC)-ICPMS.Therefore,external standardization using well-characterized natural zircon standards is fundamental for accurate microbeam measurements.While the isotopic geochronology and geochemistry laboratories equipped with microbeam analytical facilities have been increasingly established in China during the past decade,applications of the isotopic microanalysis are still limited due to shortage of available standards.We report here the Qinghu zircon as a potential new working reference for microbeam analysis of zircon U-Pb age and O-Hf isotopes.This zircon was separated from the Qinghu quartz monzonite from the western Nanling Range,Southeast China.It is fairly homogeneous in U-Pb age and Hf and O isotopes in terms of large amounts of mircobeam measurements by LA-MC-ICPMS and SIMS at the scales of 20–60 m.SIMS measurements yield consistent206Pb/238U age within analytical uncertainties with that obtained by ID-TIMS.Precise determinations of O isotopes by IRMS and Hf isotopes by solution MC-ICPMS are in good agreement with the statistical mean of microbeam measurements.We recommend U-Pb age of=159.5±0.2 Ma(2SE),18O=5.4‰±0.2‰(2SD)and176Hf/177Hf=0.283002±0.000004(2SD)as the best reference values for the Qinghu zircon.Zircon is the most useful mineral for studies in U-Pb geochronology and Hf and O isotope geochemistry. Matrix effect is a major problem of the microbeam techniques such as SIMS and LA-（MC）-ICPMS. Therefore, external standardization using well-characterized natural zircon standards is fundamental for accurate microbeam measurements. While the isotopic geochro- nology and geochemistry laboratories equipped with microbeam analytical facilities have been increasingly established in China during the past decade, applications of the isotopic microanalysis are still limited due to shortage of available standards. We report here the Qinghu zircon as a potential new working reference for microbeam analysis of zircon U-Pb age and O-Hf isotopes. This zircon was separated from the Qinghu quartz monzonite from the western Nanling Range, Southeast China. It is fairly homoge- neous in U-Pb age and Hf and O isotopes in terms of large amounts of mircobeam measurements by LA-MC-ICPMS and SIMS at the scales of 20-60 ~tm. SIMS measurements yield consistent 2~6pb/238U age within analytical uncertainties with that obtained by ID-TIMS. Precise determinations of O isotopes by IRMS and Hf isotopes by solution MC-ICPMS are in good agreement with the statistical mean of microbeam measurements. We recommend U-Pb age of = 159.5 ± 0.2 Ma （2SE）, δ^18O = 5.4‰ ± 0.2%0 （2SD） and 176Hf/177Hf = 0.283002 ± 0.000004 （2SD） as the best reference values for the Qinghu zircon.

关 键 词：锆石U-Pb年龄 Hf同位素 微束分析 天然锆石 O同位素 MC-ICPMS U-PB年代学 中国东南部 

分 类 号：P597.3[天文地球—地球化学]