Estimation of emplacement depth of the Miocene Kaikomagatake pluton in the Izu Collision Zone

Abstract

The Miocene Kaikomagatake pluton is one of the Neogene granitoid plutons exposed in the Izu Collision Zone. In order to constrain the emplacement depth of the pluton, we applied the Al-in-hornblende geobarometer (Anderson and Smith, 1995). We used samples with mineral assemblage of hornblende + biotite + plagioclase + quartz + K-feldspar + magnetite + ilmenite ± sphene. Rim compositions of hornblende were used for barometry. Applying the barometer to 8 samples yielded 2.2 - 3.6 kbar. The estimated pressures correspond to ~9 - 14 km for the emplacement depth of the Kaikomagatake pluton.