Estimation of emplacement depth for the Miocene Kaikomagatake granitoid pluton: constraints on crustal denudation history of the Izu collision zone

抄録

The Miocene Kaikomagatake pluton is one of the Neogene granitoid plutons exposed at the northern end of the Akaishi Range of the Izu collision zone, where the Izu–Bonin oceanic arc is colliding against the Honshu arc. The pluton intrudes discordantly into the Shimanto accretionary complex of the Honshu arc along the Itoigawa–Shizuoka Tectonic Line that marks the collision boundary. We applied Al–in–hornblende geobarometers to constrain the emplacement depth of the Kaikomagatake pluton. A recently proposed geobarometer suitable for relatively shallow granitoid magmas yielded 2.4–2.2 kbar at temperatures close to the water–saturated granite solidus, which corresponds to upper to middle crustal depths (~ 9–8 km). Using previously reported thermochronological data, we estimated the post–emplacement cooling rate at ~ 66–156 °C/m.y. for the pluton. The estimated cooling rate is lower than that reported for other granitoid plutons in the accreted Izu–Bonin arc, such as the Tanzawa plutonic complex and the Tsuburai pluton. The early stage of the collision between the Izu–Bonin and the Honshu arcs contributed little to denudation of the Honshu arc crust at the Kaikomagatake pluton area.