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K-Ar、~(40)Ar/~(39)Ar定年中,用以计算囚禁~(40)Ar绝对量的~(40)Ar/~(36)Ar,称为初始氩比值。现代大气中的初始氩比值叫尼尔值,为295.5。K-Ar、~(40)Ar/~(39)Ar定年的表观年龄都是在假设初始氩比值与现代大气中的尼尔值一致的基础上得到的。事实证明,地球样品的初始氩比值不总是尼尔值,因此这种假定不可靠,尤其在对年轻样品进行K-Ar、~(40)Ar/~(39)Ar定年时,会带来错误的表观年龄结果。对于K-Ar、~(40)Ar/~(39)Ar精细年代学,特别对于年轻样品和低钾含量样品,只有初始氩比值才对定年研究有意义,而初始氩比值只能通过~(40)Ar/~(39)Ar等时线法求得。所以严格地讲,只有等时线年龄才是可靠的。结合实验流程,本文分析了~(40)Ar/~(39)Ar定年中为什么大多数等时线获取的初始氩比值接近尼尔值,一是因为常规~(40)Ar/~(39)Ar坪年龄的计算方法,二是因为吸附氩的干扰。初始氩比值的一致性,被用来证明样品同位素同源和封闭特性,对年龄数据的精度及可靠性有非常大的影响,尤其是年轻样品。因此,在~(40)Ar/~(39)Ar定年中要选取氩同位素初始比值一致的同源样品,并在实验流程中尽量克服样品吸附气体。本文对传统~(40)Ar/~(39)Ar方法中坪年龄、年龄坪的意义提出了质疑,对提高~(40)Ar/~(39)Ar定年的精度具有重要意义,并使之能够应用到极年轻的火山岩定年中。
Ar ~ ~ (36) Ar used to calculate the absolute amount of ~ (40) Ar imprinted in K-Ar, ~ (40) Ar / ~ (39) Ar dating is called the initial argon ratio. The initial argon ratio in the modern atmosphere is called the Neil value, which is 295.5. The apparent age of the K-Ar, ~ (40) Ar / ~ (39) Ar dating is based on the assumption that the initial argon ratio is consistent with the Neil value in the modern atmosphere. As it turns out, the initial Argon ratio of Earth samples is not always the Neil value, so this assumption is unreliable, especially when young samples are dating K-Ar, ~ (40) Ar / ~ (39) Ar Wrong apparent age result. For the K-Ar, ~ (40) Ar / ~ (39) Ar fine chronology, especially for young and low-K samples, only the initial argon ratio is of interest for dating studies, whereas the initial argon ratio can only be approximated by ~ ( 40) Ar / ~ (39) Ar isochronism obtained. So strictly speaking, only the isochron age is reliable. In this paper, we analyze why the initial argon ratio obtained by most of the isochrones in the ~ (40) Ar / ~ (39) Ar dating is close to the Neil value. The first reason is that the conventional ~ (40) Ar / ~ Ar Ping age calculation method, the second is because of the interference of argon adsorption. The consistency of the initial argon ratio, which is used to demonstrate the isotopic homology and seal properties of samples, has a very large effect on the accuracy and reliability of age data, especially in young samples. Therefore, in the ~ (40) Ar / ~ (39) Ar dating, homologous samples with the same initial ratio of argon isotopes should be selected, and the gas adsorbed by the sample should be overcome as much as possible during the experiment. In this paper, the author questioned the significance of the plateau age and the age plateau in the Ar ~ ~ (39) Ar Ar ~ (39) method, which is of great significance to improve the accuracy of ~ (40) Ar / ~ Can be applied to very young volcanic dating.