TrekGEO > Mineral Trail > Koshinetsu region > Yamanashi pref. > Onna-Saka

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Furuseki village, Kofu city, Yamanashi pref., Japan


Prehnite-Pumpellyite facies metamorphic rocks

The Takahagi basalt and dacitic tuff of the middle Miocene (14 Ma) Ashikawa formation, the Nishi-Yatsushiro group, subjected to Prehnite-Pumpellyite facies metamorphism by the Ashikawa quartz diorite in the middle Miocene (12 Ma). The Ashikawa quartz diorite is I-type (Magnetite-series). Approximately 5 km apart from quartz diorite, the heat source. Ages of sedimentary rocks were determined by microfossils, quartz diorite by K-Ar radiometric dating of biotite and hornblende.


Outcrop of basalt of the Takahagi Basalt subjected to Prehnite-Pumpellyite facies contact metamorphism. White spots are zeolite. Most of zeolite spots in this photograph are chabazite.

Reported Minerals

  • Calcite
  • Laumontite
  • Prehnite
  • Mesolite
  • Analcime
  • Wairakite
  • Chabazite
  • Epidote
  • Pumpellyite

Mineral Assemblages

  • Laumontite - Pumpellyite
  • Quartz - Prehnite
  • Calcite - Epidote
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