Ar-Ar and U-Pb ages of petit-spot volcanic cluster on the subducting Pacific Plate

Abstract

Submarine petit-spot magmatisms induced by lithospheric flexure provide some injections into old lithosphere and submarine environment near trench prior to its subduction. Although Ar-Ar age estimates were poorly constrained for lava samples because of recoil and excess Ar, eight holocrystalline samples provide the good plateau ages. In a further attempt to determine the age of the lavas, we separated zircon crystals from peperite samples, which show upper limit of eruption age. Older zircons, moreover, were dated at various ages all younger than the crustal age, implying submarine sediments were annealed and highly disturbed due to the petit-spot magma. Our Ar-Ar and U-Pb age data of lavas and peperites provide a new understanding of the lithosphere and submarine environment of the NW Pacific Plate.