40Ar/39Ar technique of KAr dating: A comparison with the conventional technique

K-Ar ages have been determined by the⁴⁰Ar/³⁹Ar total fusion technique on 19 terrestrial samples whose conventional K-Ar ages range from 3.4 my to nearly 1700 my. Sample materials included biotite, muscovite, sanidine, adularia, plagioclase, hornblende, actinolite, alunite, dacite, and basalt. For 18 samples there are no significant differences at the 95% confidence level between the KAr ages obtained by these two techniques; for one sample the difference is 4.3% and is statistically significant. For the neutron doses used in these experiments (≈4 × 10¹⁸ nvt) it appears that corrections for interfering Ca- and K-derived Ar isotopes can be made without significant loss of precision for samples with K/Ca > 1 as young as about 5 × 10⁵ yr, and for samples with K/Ca < 1 as young as about 10⁷ yr. For younger samples the combination of large atmospheric Ar corrections and large corrections for Ca- and K-derived Ar may make the precision of the⁴⁰Ar/³⁹Ar technique less than that of the conventional technique unless the irradiation parameters are adjusted to minimize these corrections.