Concordance between K-Ar ages of K-feldspar and fission-track ages of zircon in Cretaceous granitic rocks from Japan

The closure temperature for zircon in the fission-track dating has been poorly estimated because of interpolation between minerals with very different closure temperatures. We find that K-Ar ages and fission-track ages of coexisting K-feldspars and zircons in Cretaceous granitic rocks from Japan are con-cordant within the experimental errors, with the exception of a few cataclastically deformed samples near the Median Tectonic Line. The concordance between the two systems suggests that the closure temperature for zircon in the fission-track system may be lower than 200°C.