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Tano

Tano, Yamato village, Koshu city, Yamanashi pref., Japan

Occurrence

Hydrated minerals by chemical weathering

Weathered zone in the Tonoki body of the late Miocene (10 Ma) Tokuwa Granite. The Tonoki body is the S-type (Ilmenite-series) margin of the I-type (Magnetite-series) Tokuwa Granite. The S-type (Ilmenite-series) margin was formed by reduction reation of granite magma with surrounding pelitic rocks. The shale of this locality is that of the middle Eocene (45 Ma) Magi Unit of the Sagamiko Group, a member of the Shimanto accretionary complex. Ages of sedimentary rocks were determined by radiolarians, and granite age by K-Ar radiometric dating of biotite and whole rock.

Tano

Outcrop of strongly weathered granite of the Tonoki body. Biotite in granite was altered to vermiculite by replacing K to H2O in the weathering process. There are many granite outcrops in this area but vermiculite was observed at only a few outcrops facing south. Vermiculite was not observed at weathered outcrops facing north. Is large temperature difference in a day important to vermiculite formation?

Reported Minerals

Mineral Assemblages

  • Granite(Host) - Vermiculite
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