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地质科学  2007, Vol. Issue (3): 532-557    DOI:
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K-Ar法地质年龄标准物质ZBJ角闪石的定值结果
桑海清, 王非, 贺怀宇, 王英兰
中国科学院地质与地球物理研究所岩石圈演化国家重点实验室, 北京, 100029
CERTIFIED RESULTS OF THE ZBJ HORNBLENDE REFERENCE MATERIALS FOR K-Ar AND 40Ar-39Ar DATINGS
Sang Haiqing, Wang Fei, He Huaiyu, Wang Yinglan
State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029
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摘要 为了满足K-Ar定年中K和40Ar*分析的质量监控及Ar-Ar法样品在反应堆照射时中子通量监测的需要,我国氩同位素年代学工作者研制了一个K-Ar法年龄标准物质ZBJ角闪石,它采自北京房山花岗闪长岩体。它的40Ar-39Ar阶段加热分析结果表明:40Ar*在矿物晶格中保存均匀稳定,年龄谱平坦,39Ar析出量高达97%。这些证据充分表明该黑云母结晶以后未受过热扰动,40K-40Ar*同位素计时体系封闭良好。坪年龄为133.3±0.6Ma,总气体年龄为134.4±1.4Ma,36Ar/40Ar-39Ar/40Ar反等时线年龄为133.2±0.8Ma,40Ar/36Ar初始值为297.6±4.8,此值与(40Ar/36Ar)a大气氩丰度比(295.5±0.5)处于同一范围,表明样品不含过剩氩。这几个年龄值的一致性,说明该样品具有良好的均匀性和稳定性,它作为K-Ar和Ar-Ar法地质年龄标准物质是适合的。ZBJ角闪石均匀性检验结果表明:在0.05显著性水平下经统计学方法检验,证明K和40Ar*的F分布值小于F临界值,说明该样品是均匀的。国内8个实验室参加了ZBJ角闪石K含量和40Ar*含量的定值分析,经统计学方法检验,结果显示全部定值数据都服从正态分布并具等精度。在置信概率为0.95时,40Ar*和K含量的相对标准偏差都小于1%。两个特性量值定值分析结果的一致值(认定值)和不确定度分别为:40Ar*=(2.464±0.018)×10-10mol/g,K=(1.027±0.008)%,K-Ar年龄(标准值)=133.3±1.5Ma(2σ)。此标准物质纯度为98.1%,粒度为0.15~0.30mm,总重量为740g,缩分成最小样品单元共100瓶,每瓶7.4g,可供我国K-Ar和Ar-Ar法同位素年代学实验室使用37年。
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桑海清
王非
贺怀宇
王英兰
关键词ZBJ角闪石   标准物质   均匀性检验   K和40Ar*的定值分析   统计学检验   K-Ar和Ar-Ar定年     
Abstract: The ZBJ hornblende,as K-Ar age geostandard of China,was sampled from the Fangshan granodiorite in southwestern Beijing.The granodiorite consisted of biotite,hornblende,feldspar,quartz and minor epidote,zircon,sphere,etc.About 740 g of pure ZBJ hornblende was obtained at the 0.15~0.30 mm fraction.The purity was about 98.1%.The ZBJ hornblende belonged to the kind of normal biotite mineral according to the chemical composition,X-fluorescence spectrum and X-ray diffraction.Following mixing,the ZBJ hornblende was divided into 10 jars,each one being about 74 g.Each jar sample was further subdivided into 15 aliquots about 7.4 g each(total 100 aliquots).One aliquot(prefixed C) was retained for control analysis of K and 40Ar*,the other 9 aliquots of the same jar remained to be used for interlabortory work.40Ar-39Ar age spectrum of the ZBJ hornblende indicated that the hornblende had remained undisturbed since its crystallization and cooling.The plateau age(5~16 steps) and total gases age(1~16 steps) were 133.3±0.6 Ma and 134.4±1.4 Ma respectively.The argon extraction occurred mainly between 940~1500 ℃,and about 96.9% radiogenic 40Ar could be released at that temperature range.From the data of 5~16 steps heating the isochron age and the initial 40Ar/36Ar ratio of the hornblende was 133.2±0.8 Ma and 297.6±4.8 Ma respectively.The MSWD in the 36Ar/40Ar-39Ar/40Ar inverse isochron diagram was 0.36.The homogeneity tests and the certification analyses of 40Ar* and K in ZBJ hornblende were performed according to the rules from the “International Standard Organization(ISO) Guid 35(1985)” and “Primary Reference Material Technique of China(1994)”.During the homogeneity tests the analyses of K and 40Ar* in the samples of 77600 hornblende,Hb3gr hornblende and GA1550 biotite were done and the results were almost coincident with their mean value published.The homogeneity tests were performed in Ar isotopic laboratory of Institute of Geology and Geophysics,Chinese Academy of Science.The sample weights were 30 mg for 40Ar* and 60 mg for K.Statistical estimate of analytical data showed that F values of K and 40Ar* were less than their critical F values.The test results indicated that the uncertainty caused by homogeneity of the sample was 0.57% for radiogenic 40Ar* and 0.78 % for K,respecitively.A good reproducibility of analysis obtained.Accordingly,the mininum weight of about 16 mg of recommended sample should be proper.Eight laboratories accepted the invitation to participate in calibrations of 40Ar* and K of the ZBJ hornblende.K-calibrations were done with flame photometry and atomic absorption using 40Ar-39Ar technique.The calibrations of 40Ar* were performed by using isotopic dilution method,38Ar spike and 40Ar-39Ar techniques.The Grubbs and Dixon tests demonstrated that there was no outlier in all data from the 8 laboratories.The calculations of skewness and kurtosis coefficients,and the Cochran isoprecision indicated that all data of K and 40Ar*,obeyed a normal distribution.The certificate values for 40Ar* and K of the ZBJ hornblende were calculated as follows(with 95% confidence level):40Ar*=(2.464±0.018)×10-10mol/g,K=(1.027±0.008)%.The K-Ar age,from Ke=0.581×10-10/a,KB=4.962×10-10/a and 40K/K=1.167×10-4(atom/atom),was calculated to be 133.3±1.5 Ma(2σ).
Key wordsThe ZBJ hornblende   Reference matrials   Homogeneity chek   Certification of K and 40Ar*   Statistical tests   K-Ar and 40Ar-39Ar datings   
收稿日期: 2006-08-04;
基金资助:中国科学院地质与地球物理研究所岩石圈演化国家重点实验室专项资金资助
引用本文:   
桑海清,王非,贺怀宇等. 2007, K-Ar法地质年龄标准物质ZBJ角闪石的定值结果. 地质科学, (3): 532-557.
Sang Haiqing,Wang Fei,He Huaiyu et al. CERTIFIED RESULTS OF THE ZBJ HORNBLENDE REFERENCE MATERIALS FOR K-Ar AND 40Ar-39Ar DATINGS[J]. Chinese Journal of Geology, 2007, (3): 532-557.
 
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[1] 桑海清 王松山 王非 王英兰. K-Ar法年龄标准物质ZGC粗面岩K和40Ar*含量及年龄的定值结果[J]. 地质科学, 2010, 45(03): 885-904.
 
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