Abstract: Precise measurement of Argon is considered to be one of the most important geochronological subjects in K-Ar dating of young volcanic materials. Based on the presumption that ⁴⁰Ar/³⁶Ar ratio is equal to 295.5 during conventional K-Ar dating, it has been studied that dating was constrained in some cases, especially for young samples. A technique of unspiked Argon measurement has been improved and applied in recent years. The merits for this method are that argon will not be contaminated by spike ³⁸Ar systematically, thus, the contents of ⁴⁰Ar, ³⁸Ar and ³⁶Ar will be measured by calibrating with standard atmosphere. Considering the interference of mass fractionation of argon in volcanic rocks, it is allowed to calibrate ⁴⁰Ar/³⁶Arratio with ³⁸Ar/³⁶Ar ratio of the sample. Therefore, radiogenic ⁴⁰Ar^* and age of sample will be calculated accurately. At present, unspiked K-Ar dating has been widely used in geological researches. It is able to acquire reliable ages including late Tertiary and Quaternary to interpret the geological events and reconstruct the magmatic history. It implies that, for K-Ar chronology, a powerful means and approach will be used to study volcanic rock younger than late Tertiary by introducing the principle and geological application of unspiked K-Ar dating.

Key words: unspiked K-Ar dating, ³⁸Ar/³⁶Ar ratio, ⁴⁰Ar/³⁶Ar ratio, standard atmosphere, young volcanic rock

摘要： 年轻火山物质K-Ar定年中Ar的精确测量一直是地质年代学研究的重要课题。在常规K-Ar定年法中，样品外来氩的⁴⁰Ar/³⁶Ar比值被假定为295.5。但研究表明，这种假定在某些情况下，尤其是在年轻样品的测量中受到了限制。一种无稀释剂的测Ar技术已在近年来得到了发展和应用。该方法的优势在于测氩系统不受³⁸Ar稀释剂的混染，利用标准大气的校准可测得样品中的⁴⁰Ar、³⁸Ar和³⁶Ar。考虑火山岩中大气氩分馏造成的影响，利用测得的³⁸Ar/³⁶Ar比值还可以对所测样品中的外来⁴⁰Ar/³⁶Ar比值进一步加以校正，给出精确的放射性成因⁴⁰Ar^*含量计算和K-Ar定年。目前，无稀释剂的K-Ar定年技术在地质上已有广泛应用，并能取得晚第三纪到第四纪可靠的年龄，对地质事件做出合理地解释和重建岩浆活动历史。对无稀释剂法K-Ar定年原理及地质应用的介绍，将为K-Ar年代学应用于研究晚第三纪以来的年轻火山岩提供一种有力的手段和解决途径。

关键词: 无稀释剂法K-Ar定年, ³⁸Ar/³⁶Ar比值, ⁴⁰Ar/³⁶Ar比值, 标样大气, 年轻火山岩