Qinghu zircon: A working reference for microbeam analysis of U-Pb age and Hf and O isotopes |
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Authors: | XianHua Li GuoQiang Tang Bing Gong YueHeng Yang KeJun Hou ZhaoChu Hu QiuLi Li Yu Liu WuXian Li |
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Institution: | 1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China 2. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China 3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China 4. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China 5. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
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Abstract: | 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 μm. SIMS measurements yield consistent 206Pb/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‰ (2SD) and 176Hf/177Hf = 0.283002 ± 0.000004 (2SD) as the best reference values for the Qinghu zircon. |
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Keywords: | Qinghu zircon standard U-Pb age O and Hf isotopes SIMS LA-MC-ICPMS |
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