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Kosugi, Ogose city, Iruma county, Saitama pref., Japan


Pumpellyite-Actinolite facies high-P metamorphic rocks

Minerals in pelitic schist in the Late Jurassic (150 Ma) to Early Cretaceous (130 Ma) accretionary complex subjected to Pumpellyite-Actinolite facies metamorphism as a low grade part of the high-P Sambagawa metamorphic belt in the Late Cretaceous (70 Ma). The Sambagawa metamorphic rocks is considered that it has been near the ground surface since early Paleocene (65 Ma). Metamorphic age was determined by K-Ar radiometric dating of muscovite.


Outcrop of pelitic schist of Sambagawa Metamorphic Rocks associated with lawsonite, an index mineral for high-P metamorphism. The massive gray part above the coin is metachert, and the lower black part is pelitic schist. This is the historical outcrop where Professor Yotaro Seki of Saitama University first reported lawsonite from Kanto Mountains in 1957.

Reported Minerals

  • Lawsonite
  • Epidote

Mineral Assemblages

  • Lawsonite - Quartz - Mica
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