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| Intercalibration of the ZBH-15 Biotite Reference Material Utilized for K-Ar and 40Ar-39Ar Isotopic Dating in China |
| SANG Hai-qing, WANG Fei, HE Huai-yu, WANG Ying-lan |
| State Key Laboratory of Lithsphere Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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Abstract ZBH-15 biotite has been successfully studied for K-Ar and 40Ar-39Ar dating purpose by argon isotope chronologist of Chinese.The biotite,as fist K-Ar age standard material of China,were separated from Fangshan granodiorite complex in the southwest of Beijing,which occupies an area of 47 km2.About 2070 g of pure ZBH-15 biotite was obtained at the 0.15-0.25 mm fraction.The purity is about 99.8%.Following mixing,the ZBH-15 biotite was divided into 15 jars about 138 g each.Each jar sample was further subdivided into 15 aliquots about 9.2 g each(total 225 aliquots).40Ar-39Ar age spectrum of ZBH15 biotite indicates that the biotite has remained undisturbed since its crystallization.The plateau age(3-13 steps) and total gases age(1-13 steps) are 132.2±0.2Ma and 131.3±0.5 Ma.The argon extraction occurs mainly between 750-1400℃,and about 98.3% radiogenic 40Ar can be released at that temperature rang.From the data of 3-14 steps heating the isochron age and the initial 40Ar/36Ar ration of the biotite are 132.3±0.8 Ma and 293.9±1.4 Ma, respectively.The correlation coefficient and MSWD in the isochron diagram are 0.99999 and 0.3,respectively.The homogeneity tests were performed in Ar isotopic laboratory of Institute of Geology and Geophysics,Chinese Academy of Science.The sample weights are 15 mg for 40Ar* and 60 mg for K.Statistical estimate of analytical data show that F values of K and 40Ar* are less than their critical F values.The test results indicate that the uncertainty caused by homogeneity of the sample is 0.11% for radiogenic 40Ar* and 0.15% for K,respecitively.Seven laboratories,accepted the invitation to participate in calibrations of 40Ar* and K of ZBH-15 biotite.K-calibrations have been done with flame photometry and atomic absorption.The calibrations of 40Ar* were performed by isotopic dilution method,38Ar spike and 40Ar-39Ar techniques.The Grubbs and Dixon tests indicate that there is no outlier in all data from 8 laboratories.The calculations of skewness and kurtosis coefficients,and the Cochran isoprecision indicate that all data of K and 40Ar*,obey a normal distribution.The certificate values for 40Ar* and K of ZBH-15 biotite are calculated as follows(with 95%confidence level): 40Ar*=1.814±0.014(10-9 mol/g),K=7.59±0.02(%).The K-Ar age,from λe=0.581×10-10/a,λβ=4.962×10-10/a and 40K/K=1.167×10-4(atom/atom),was calculated to be 132.8±1.3Ma(2σ).
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Received: 07 April 2006
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XU Jing-chi, GU Xue-xiang, WANG Jia-lin, ZHANG Yong-mei, HE Ge, ZHOU Chao, LIU Rui-ping. Zircon U-Pb Geochronology, Geochemistry and Geological Significance of Granites from the Sanfengshan Cu-Au Deposit in Southern Beishan Orogenic Belt, Xinjiang[J]. Acta Metallurgica Sinica, 2018, 37(2): 294-306. |
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