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通过国内外花岗岩体的412对角闪石-黑云母40Ar-39Ar年龄(tAr)与锆石U-Pb年龄(tZr)之间差值ΔtZr-Ar(tZr-tAr)进行的频数统计分析表明:ΔtZr-Ar呈对称正态分布(偏度系数CSK==-0.276,峰度系数CKU=16.52);ΔtZr-Ar既呈正值又有负值,其众数值为0.70Ma,均值为1.15Ma。采用最小二乘法计算,花岗岩体锆石U-Pb年龄与花岗岩角闪石-黑云母40Ar-39Ar年龄拟合出相关系数很高(R=0.996),回归系数接近l的线性回归方程(tAr=1.00453×tZr-1.932)。这些统计特征表明花岗岩角闪石-黑云母40Ar-39Ar定年测定结果与锆石U-Pb定年测定结果在允许的误差范围内是一致的,不存在花岗岩锆石U-Pb年龄>角闪石40Ar-39Ar年龄>黑云母40Ar-39Ar年龄的规律。结合Dodson’s矿物封闭温度计算公式中存在问题的剖析,本文得出结论,按Dodson’s公式计算得出的花岗岩矿物40Ar-39Ar封闭温度不能代表从花岗岩浆晶出造岩矿物40Ar-39Ar体系的封闭温度。
Through the statistical analysis of the frequency difference ΔtZr-Ar (tZr-tAr) between the 412-diabase amphibole-biotite 40Ar-39Ar ages (tAr) and zircon U-Pb ages (tZr) ΔtZr-Ar showed a symmetric normal distribution (skewness coefficient CSK == - 0.276, kurtosis coefficient CKU = 16.52); ΔtZr-Ar was both positive and negative, with a mode of 0.70Ma and a mean of 1.15Ma. According to the least-square method, the U-Pb ages of granite bodies are highly correlated with the ages of 40Ar-39Ar ages of the amphibole-biotite granites (R = 0.996), and the linear regression equation with regression coefficients close to 1 (tAr = 1.00453 × tZr-1.932). These statistical features indicate that the 40Ar-39Ar dating of granites is consistent with the zircon U-Pb dating within the allowable error range, and there is no granite-zircon U-Pb age> amphibole 40Ar -39Ar age> age of 40Ar-39Ar biotites. Based on the analysis of the Dodson’s formula for calculating the closure temperature of mineral, the conclusion of this paper is that the 40Ar-39Ar closure temperature of the granite mineral calculated by Dodson’s formula can not represent the closure temperature of the 40Ar-39Ar system derived from the granitic magma.