摘要
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。
The frequency statistics analysis was conducted for 412 pairs of difference values ΔtZr-Arbetween the hornblendbiotite40Ar-39 Ar ages（tAr） and zircon U-Pb ages（tZr） of granite plutons worldwide. The result indicated that the ΔtZr-Ar（tZr-tAr） displays a symmetrical normal distribution with a skewness coefficient of CSK=-0. 267 and a kurtosis coefficient of CKU= 16. 52 in the histogram,both positive and negative tZr-Avalues were observed and their mode and mean are 0. 70 Ma and 1. 15 Ma,respectively. Using the least square regression procedure,a best liner regression equation（tAr= 1. 00453 ×tZr-1. 932） was fitted for zircon U-Pb ages（tZr） and hornblend-biotite40Ar-39 Ar ages（tAr） of granite plutons with a correlation coefficient as high as R = 0. 996 and a regression coefficient closed to 1. These statistical analysis characteristics indicated that the hornblend-biotite40Ar-39 Ar dating results are consistent with zircon U-Pb dating results for granites within the permissible error,therefore the rule of hornblende40Ar-39 Ar dating ages〉biotite40Ar-39 Ar dating ages is not statistically correct. It implicated that the40Ar-39 Ar closure temperature of hornblend-biotite is same as the U-Pb closure temperature of zircon. Based on these statistic analyses and the query for Dodson’s Formula,it is concluded that the closure temperature of40Ar-39 Ar isotope system estimated by the Dodson’s formula cannot represent the closure temperature of40Ar-39 Ar isotope system in the rock-forming minerals crystallized from the granite magma.
出处
《矿物岩石地球化学通报》
CAS
CSCD
北大核心
2015年第1期93-100,共8页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
中国核工业地质局十二五科技项目(2011-D03)
内生金属矿床成矿机制研究国家重点实验室开放项目(2008-Ⅰ-04)
