Ol-P1-basalts from the drill holes 495 and 500 from the deep-sea drilling Pacific Ocean trench were analyzed by K-Ar and 39Ar-40Ar methods. The rock consists of P1- phenocrysts (0.3-1.0 mm size) and volcanic glass. The former is transformed to the fine-grained aggregate. The comparison of the integral values of the 39Ar-40Ar age and K-Ar age display that calculated 39Ar-40Ar age is twice as much as K-Ar age.
This difference may be induced by 39Ar recoil losses (Turner et al., 1974; Villa et al., 1983). The possibility of recoil losses control is allowed by the use of 39Ar as tracer i step-heating measurements. For that purpose the amount of 39Ar can be converted to the amount of potassium (in the samples) using the amount of K in the monitor. The data show that recalculated amount of K is twice as low than the original one. At the same time the contents of 40Ar coincide for both 39Ar-40Ar and K-Ar methods.
Sometimes the control 39Ar recoil losses was made by the irradiation of the samples placed in to the quartz ampoules followed by gas analysis (Lippolt et al., 1986). The control method applied by us include the 38Ar as a tracer in step-heating measurements. The criterion of the absence of the neutronogenic distortion is the equality of 39Ar-40Ar ad K-Ar ages.
Turner, G. et al., Geochim. Cosmochim. Acta Suppl. 5, 1601-1615 (1974).
Villa, I.M. et al., Earth Planet. Sci. Lett. 63, 1-12 (1983).