Journal of The School of Marine Science and Technology,Vol.1 No.1
Petrologic study of volcanic rocks from the Mafujiyama Formation in Ryuso Group
Genjyu YAMAMOTO, Seishi TAKANO and Yong Ui KIM
Abstract
The middle Miocene Mafujiyama Formation is distributed in the southwest part of the South Fossa Magna. The
Mafujiyama Formation consists of subaqueous volcanic rocks, such as hyaloclastite. This Formation is divided into the
Jizoutouge rhyolite and the Monjyudake trachyte members.The Jizoutouge rhyolite member consists of volcanic rocks and
mudstone. These volcanic rocks consist of rhyolite and trachyte. The Monjyudake trachyte member consists of volcanic
rocks and mudstone. The volcanic rocks consist of the trachyte, trachyandesite and alkaline basalt. SiO2 contents ranges
from 50.51 to 74.94％. As FeO/MgO versus some oxide and minor element contents shows linear relation.There are three
type fractional crystallization.From the above data,it is suggested that the Mafujiyama formation forming volcanic rocks
consist of alkali rocks and subalkli rocks series. Volcanic rocks of the Mafujiyama formation can be assumed to erupt in
the tensional place based upon petrologic character.