Geohistory - Rocks from Continental to Sea Periods
Gneiss from 50 mln years ago is the oldest type of rock in the Oki Islands. Since at that time Japan was part of the supercontinent, it tells us about how the Japanese Archipelago was formed. Oki gneiss started as sand and mud sediments at the bottom of the sea. Tectonic plate subduction relocated them 15 km underground, where head and pressure transformed them into a rock with a white and black striped pattern.