Geochemical characteristics and petrogenesis of the Kaikomagatake granitoid pluton in northwestern part of the Izu Collision Zone

Abstract

Miocene granitic plutons such as Tanzawa, Kofu and Kaikomagatake are widely exposed in the Izu Collision Zone. We examine petrographical, geochemical and Sr-isotopic characteristics of the Kaikomagatake pluton exposed in northwestern part of the collision zone and discuss its petrogenesis. We conclude that Kaikomagatake pluton evolved by crystal fractionation process from primary magma (SiO₂=∼68wt%) and the primary magma were formed by anatexis of the K-rich source compositionally similar to the rocks occurring in the back arc side of the Izu-Bonin arc.