Abstract: K-Ar and Ar-Ar dating is one of the best dating method to Mesozoic-Cenozoic volcanic rocks. Appropriate size and preprocessing procedure are important for the method to get good data. 60～80 mesh (0.28～0.18mm) sample size is needed for both the need of homogeneity of a sample and to remove atmospheric argon contamination. Thin nitric acid is used to remove out the carbonatization of fresh volcanic rocks. For slightly altered rocks, 6% hydrofluoric acid is needed to etch the rocks and the age would be change up to 20% comparing to original rocks. Magnetic separation can remove the influence of xenocrysts and its age could lower 5%～10%.

Key words: volcanic rocks, preprocessing, K-Ar dating, age correction

摘要： K-Ar和Ar-Ar法是中、新生代火山岩最有效的测年方法之一，合适的粒度和有效的预处理程序对于提高年龄资料的质量至关重要。样品粒度选用60～80目粒级（0.28～0.18mm）既能保证样品的均匀性，又可以有效去除大气氩的污染。新鲜火山岩需要用稀硝酸浸泡，以去除可能的碳酸盐的影响；轻微蚀变的火山岩则须用6%氢氟酸浸泡5 min，对年龄值的矫正可达20%。用电磁选的方法可以在很大程度上剔除捕虏晶的影响，对年龄值的矫正可达5%～10%。

关键词: 火山岩, 预处理, K-Ar定年, 年龄值矫正