“花岗岩锆石U-Pb年龄能代表花岗岩侵位年龄”质疑——花岗岩锆石U-Pb年龄与全岩Rb-Sr等时线年龄对比证据  

Doubts about "the Representation of Zircon U-Pb Age to the Emplacement Age of Granite" :Evidence of Comparision between the Zircon U-Pb Ages and the Whole-Rock Rb-Sr Ages of Granite Plutons

作　　者：章邦桐[1] 吴俊奇[1] 凌洪飞[1] 陈培荣[1] 

机构地区：[1]南京大学内生金属矿床成矿机制研究国家重点实验室及地球科学系,南京210093

出　　处：《地质论评》2008年第6期775-785,共11页Geological Review

基　　金：国家自然科学基金资助项目(批准号40372036;40221301)的成果

摘　　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(tRb)之间差值Δt(Δt=tZr-tRb)进行的频数统计分析表明:Δt直方图呈对称正态分布(偏度系数CSK=0.150;峰度系数CKU=4.274);Δt既有正值又有负值;Δt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l(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Δt众数(2.0Ma)基本一致。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定年测定结果是一致的,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.

关 键 词：花岗岩侵位年龄 锆石U—Pb年龄 全岩Rb—Sr等时线年龄. 

分 类 号：P597.3[天文地球—地球化学]