Abstract
The (40)Ar/(39)Ar dating method holds particular significance for determining the age of basic rocks. However, the presence of extraneous argon ((40)Ar(E)) in some samples generates complex (40)Ar/(39)Ar age spectra, compromising the technique's utility in modern geochronology. This investigation focuses on deciphering the occurrence of (40)Ar(E) within a diabase and proposes strategies to mitigate its influence. Our results reveal distinct age patterns: separated feldspar yields a well-defined plateau age of 48.73 ± 0.07 (0.12) [2.06] Ma (2σ, MSWD = 0.86, P = 62%), while whole-rock analyses produce saddle-shaped age spectra. Through integration of EPMA major element data, K/Ca ratios from (40)Ar/(39)Ar results, and TIMA-derived mineral proportions, we identify metamorphosed amphibole as the primary host of (40)Ar(E) in this study. Thus, separated components containing metamorphosed amphiboles should be excluded as suitable targets for (40)Ar/(39)Ar geochronology. These findings provide critical guidance for sample selection and interpretation in basic rocks.