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

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