Geohistory - Rocks from Volcanic Islands Period
"Mantle xenolith is a rock brought from the mantle to the Earth's surface by the upward motion of magma. Basaltic rocks from 4-2 mln years ago on the eastern coast of Dogo Island feature black pyroxene and yellow-green olivine. Both contain minerals from the upper part of the Earth's mantle. It is thought that basaltic magma brought them from a depth of 10 km under the Earth's surface.
Mantle xenolith is also called a letter from inside of Earth. Apart from Oki Islands, we can see them in places on the west coast of Honshu, such as Ichinomegata in Akita Prefecture and Kurose in Fukuoka Prefecture. It thus gives us important clues on the composition of Earth's mantle beneath the Sea of Japan. "