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Asahine, Higashi-chichibu city, Chichibu county, Saitama pref., Japan


Pumpellyite-Actinolite facies high-P metamorphic rocks

Minerals in gabbro of the Mikabu Greenrocks associated with the Middle Jurassic (170 Ma) Kamiyoshida unit or the Early Cretaceous (120 Ma) Kashiwagi unit, members of the Northern Chichibu accretionary complex. The Mikabu Greenrocks is probably a part of the Middle Jurassic to Early Cretaceous accretionary complex cropped out between the Nothern Chichibu acretional complex and the Sambagawa metamorphic rocks. The Mikabu Greenrocks are composed of Carboniferous to Triassic Basalt lava, basaltic tuff breccia, basaltic tuff, and gabbro, and has been subjected to Pumpellyite-Actinolite facies metamorphism as a low grade part of the Sambagawa metamorphic belt in the Late Cretaceous (100 Ma). The protolith of the Mikabu Greenrocks is considered as mafic volcanic rocks and ultramafic rocks of oceanic plateaux and seamounts. Ages of sedimentary rocks were determined by conodont, and metamorphic age by K-Ar or Ar-Ar radiometric dating of muscovite.


Outcrop of meta-gabbro of the Mikabu Greenrocks. The host is composed of white plagioclase and dark green amphibole. This gabbro has been subjected to Pumpellyite-Actinolite faices metamorphism. The dark green vein under the coin is the vein of pumpellyite-(Al). Veins of white albite were also observed.

Reported Minerals

Mineral Assemblages

  • Pympellyite-(Al)
  • Albite
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