Plutonic Rock
Overview
Plutonic rocks produced in an island arc formed by subduction of ocean plates under the east margin of the Eurasian continent.
I-type Granite, S-type Granite, A-type Granite, Granodiorite, and Diorite were intruded in the accretionary complexes. Granite is classified to I-type (Magnetite-series) granite, S-type (Ilmenite-series) granite, and A-type granite. I-type (Magnetite-series) granite distributes in the continental (back-arc) side in the Southwestern Japan (Eurasian plate), whereas it distributes in the trench (fore-arc) side in the Northeastern Japan (North American plate). On the other hand, S-type (Ilmenite-series) granite distributes in the trench (fore-arc) side in the Southwestern Japan (Eurasian plate), whereas it distributes in the continental (back-arc) side in the Northeastern Japan (North American plate). Both I-type and S-type granite distributes in Fossa Magna, the boundary between the Southwestern Japan and the Northeastern Japan. A-type granite is very rare in Japan. Grabbro (M-type granite) and Pridotite are a part of accretionary complexes as fragments of oceanic plates. Lamprophyre is oberved as small dykes.
Plutonic rocks in the southwest Japan is classified into 3 zones from the Median Tectonic Line to north side: Ryoke Belt, Sanyo Belt, Sanin Belt.