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沉积岩全岩用Rb——Sr法测定同位素年龄时,往往根据在Sr~(87)/Sr(86)和R~b(87)/Sr~(86为座标的图上,样品点成一直线(等时线),拟合优度高,认为锶同位素均一化程度高,年龄值可信度高。但有些线性良好的“等时线”,并不一定是锶同位素均一化程度高形成的。一组由不同比例碳酸盐与粘土矿物组成的混合物,同样可以在等线图上表观为非常好的线性排
When the isotopic age of sedimentary rocks is determined by the Rb - Sr method, the isotopes are often found on the basis of the coordinates of Sr 87 / Sr 86 and R 87 87 / Sr 86, Isochron), the goodness of fit is high, and it is considered that the strontium isotopes have a high degree of homogeneity and a high confidence in the age value. However, some linearly good “isochrone lines” are not necessarily formed by the high homogeneity of strontium isotopes. A group of mixtures consisting of carbonate and clay minerals in different proportions can also be viewed as a very good linear array on an isogram