Abstract
Degassing process of argon from young geological materials by low temperature stepwise heating was examined to improve the precision on K–Ar dating of the materials. The radiogenic argon was released out from the groundmass, biotite, hornblende and plagioclase phenocrysts of volcanic rocks at temperatures higher than 500°C, and from sericite at temperatures higher than 400°C. Therefore, pre-heating before argon analysis is necessary; at 400°C for 1 hour for volcanic materials and at 300°C for sericites to remove the adsorbed atmospheric argon on them. HCl treatment for sericites having impure materials improves the precision, and HF treatment of volcanics which have a glassy surface produced as a result of the crushing process would improve the precision.
