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Minano, Minano city, Chichibu county, Saitama pref., Japan


Greenschist facies serpentinite

Serpentinite in the Late Jurassic (150 Ma) to Early Cretaceous (130 Ma) accretionary complex subjected to Greenschist facies metamorphism as a part of the high-P Sambagawa metamorphic belt in the Late Cretaceous (70 Ma). This serpentinite block is lens-shaped and is concordant with schistosity of the Sambagawa metamorphic rocks. The Sambagawa metamorphic rocks are considered that it has been near the ground surface since early Paleocene (65 Ma). The origin of this serpentinite block is considered as sedimentary serpentinite mélange from serpentinite seamounts at the fore-arc slope. Metamorphic age was determined by K-Ar radiometric dating of muscovite.


Outcrop of serpentinite in the Sambagawa Metamorphic Rocks. The dark green host is serpentinite, and the grayish-green veins are antigorite. Antigorite is fibrous and elongated obliquely to the vein wall. Microscopic jadeite has been reported from this outcrop.

Reported Minerals

Mineral Assemblages

  • Serpentinite - Antigorite
  • Diopside
  • Serpentinite - Jadeite
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