内容提要:通过花岗岩体的64对锆石U—Pb年龄(tZr)与全岩Rb-Sr等时线年龄(fRb)之间差值△t(△t=tZr-tRb)进行的频数统计分析表明:位直方图呈对称正态分布(偏度系数CSK=0.150;峰度系数CKU=4.274);△t既有正值又有负值;△t的众数值为2.0Ma,但远低于花岗岩基冷却-结晶所需的时间(〉16Ma);采用最小二乘法计算,花岗岩体64对锆石U-Pb年龄(tZr)和全岩Rb-Sr等时线年龄(tRb)拟合出相关系数很高(r=0.9967),回归系数接近1(斜率为0.99354)的线性回归方程(tRb=0.99354tZr=2.15163)。该回归方程的常数项(2.15163Ma)与出众数(2.0Ma)基本-致。这些特征表明,从总体来看,花岗岩体的全岩Rb—Sr等时线定年测定结果与锆石U—Pb定年测定结果是-致的,从而为花岗岩锆石U-Pb年龄不能代表花岗岩侵位年龄提供了证据。
The frequency analysis of 64 coupled age differences(△t= tZr-tRb)between the zircon U-Pb age(tZr) and whole rock Rb-Sr age (tRb)for granite plutons shows that theAt histogram displays a symmetrical normal distribution (skewness CSK= 0. 150; kutrocess CKU = 4. 274); theAt are both positive and negative with mode 2. 0Ma, but far less than the period of cooling--crystallization (〉 16 Ma)of a granitic batholith. Using least squares regression procedure, a best regression equation (tRb = 0. 99354tZr + 2. 15163) with high correlation coefficient (r=0. 997) is fitted to the 64 points of the zircon U-Pb age and the whole rock Rb-Sr age for granite plutons. The constant of this regression equation (2. 15163Ma) is consistent with theAt mode (2.0Ma) for the main. These statistical characteristics indicate that the zircon U-Pb dating age is corresponded with the whole-rock Rb-Sr isochron age for granite as a whole and the zircon U-Pb dating age cannot represents the emplacement age of a granite batholith.