ABSTRACT

Based on the ⁴⁰Ar-³⁹Ar results for Deccan Traps samples, we have investigated the relationships between the ⁴⁰Ar-³⁹Ar age release pattern and conditions of basaltic samples. ⁴⁰Ar-³⁹Ar age release patterns are divided into five types, which might be related to the conditions of samples such as their petrological textures and alteration state. A peak of non-radiogenic component of Ar is observed at the temperature around 800°C in the Ar release patterns of Deccan Traps samples. Based on the above observations, criteria for sample selection and data treatment for the ⁴⁰Ar-³⁹Ar dating are summarized as follows. (1) It is recommended to use fresh samples as much as possible and minimize the use of samples which contain mesostasis. (2) Fine-grained holocrystalline rocks are preferable to get reasonable ⁴⁰Ar-³⁹Ar ages. (3) If a sample is affected by secondary alteration and shows a high ³⁶Ar release in the intermediate temperature fractions, in age calculation it is better to exclude the isotopic data for the temperature fractions lower than about 800°C where the high ³⁶Ar release is observed.