Petrographic evidence for re-melting of granitoids in deep crust of active continental margin: an example of granitic rocks in the Kajishima, Ehime Prefecture, southwest Japan

Abstract

In Kajishima, granitoid dykes intrude into Cretaceous gabbroic rocks. The granitoids are divided into deformed and massive granitoids based on field occurrence. Massive granitoid shows equigranular texture and consists mainly of quartz, plagioclase, alkali feldspar, and biotite. Poikilitic alkali feldspar including euhedral to subhedral quartz, plagioclase and biotite is locally observed in the massive granitoid. Petrographic data together with phase relationship in granodiorite system suggest that the poikilitic texture indicates partial melting of quartz- and plagioclase-bearing rocks such as tonalite and granodiorite. The presence of this texture in the Kajishima granitoids suggests re-melting of tonalite/granodiorite at deep arc crust.