Orbicular rocks in the Takakuma granite, Osumi peninsula (I)

Abstract

Orbicular rocks which are characterized by tourmaline were found from the central part of the Takakuma granite mass in the Osumi peninsula, Kagoshima Prefecture. The mode of occurrences, microscopic features, optical properties, twin types of plagioclase, volume ratios of the constituent minerals, estimated chemical composition from mode, and trace elements are given.
It is concluded that the formation of the rocks related to the greisenization and concentration of the boron-rich volatile towards the central part of the granite mass during the deuteric stage of the magmatic cooling.