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Nagusa-Kamicho, Ashikaga city, Tochigi pref., Japan


Hornblende-hornfels facies contact metamorphic rocks

Early Jurassic (200 Ma) shale has been subjected to hornblende-hornfels facies contact metamorphism by the Late Cretaceous (85 Ma) Ashikaga granodiorite, and andalusite was formed in it. This shale is the matrix of the Middle Jurassic (170 Ma) Kurohone-Kiryu Unit. The Kurohone-Kiryu Unit corresponds to the Kanayama Unit of the Tamba-Mino-Ashio accretionary complex. The Ashikaga granodiorite is S-type (Ilmenite-series). Approximately 100 m apart from the Ashikaga granodiorite, the heat source. Ages of sedimentary rocks were determined by radiolarians, and granodiorite by K-Ar radiometric dating of biotite.


Outcrop of andalusite-hornfels formed by hornblende-hornfels facies metamorphism of mudstone, a matrix of the Kurohone-Kiryu Unit. The black outcrop is composed of andalusite-bearing hornfels, and flat schistosity was recognized. Andalusite is too small to see in this photograph but they are clear pale pink and aligned along schistosity.

Reported Minerals

  • Andalusite
  • Pyrite

Mineral Assemblages

  • Hornfels - Andalusite - Pyrite
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