Neo-Granitic Pluton and Later Hydrothermal Alteration at the Kakkonda Geothermal Field, Japan

Abstract

A neo-granitic pluton ranging from adamellite to quartz diorite exists at depth at the Kakkonda geothermal field. The intrusion of the pluton is younger than The metamorphosed area covers over The pluton underlies about below the biotite isograd and about 600-700m below the cordierite isograd. There are productive fractures in the pluton, on surface of the pluton and in the metamorphosed rocks. contraction caused by cooling of the magma is one of the main reasons of the formation of the fractures. The pluton is fresh, however there is a little hydrothermal alteration along the fractures. The hydrothermal minerals distribute in the metamorphic rocks. Wairakite distributes extensively in the 230-260?C zone, and is characteristic in that zone. It distributes below the biotite isograd. These facts tell that the pluton is a part of the heat source and that convection.