Source disversity of the older and early Mesozoic granitoids in the Hida Belt,central Japan.

Abstract

The older granitoids and the early Mesozoic plutonic rocks were studied for 18 O value, magnetic susceptibility, and major and minor elements. The older granitoids belong to ilmenite series and have 18 O higher than 9.8 ‰ (averaged 10.5 ‰), but the early Mesozoic plutonic rocks belong to magnetite series and have 18 O values lower than 9.1 ‰ (average 7.9 ‰); the inverse correlation between 18 O value and magnetic susceptibility, everywhere observed in the Cretaceous and Tertiary granitic terrains in Japan, is also true in the Hida Belt. Many of the older granitoids show high Sr/Y ratios. This is the first time to find adakitic ilmenite series in the Phanerozoic granitoids of the Circum-Pacific rim. The adakitic components are also involved in the early Mesozoic plutonic rocks, especially those of the inner Hida belt where mingling with the crustal components is suggested. The adakitic character can be generated in a diversity of the origins, besides the slab melting.