KAr ages of submarine basalts dredged from seamounts in the western pacific area and discussion of oceanic crust

Abstract

KAr ages of 16 submarine basalts dredged from 5 seamounts in the Western Pacific area are presented. The KAr ages range from 30 my to 80 my. Because of large amounts of radiogenic argon in these samples (more than 10 −10 moles/g), excess argon would not affect the KAr ages significantly and the discordant KAr ages can be best explained by diffusion loss of radiogenic argon. We conclude that the KAr ages obtained here can give at least a good estimate of minimum age of the seamounts. In the Western Pacific area, the KAr ages of the seamounts lie between the Cretaceous and the Early Tertiary in marked contrast to the relatively quiet volcanic activity in the Western Pacific Island arcs. Likelihood of the long time span for the growth of seamounts (more than 10 my) sets a minimum depth of 50 km to the supposed moving oceanic layer.