PETROLOGY OF THE MUROTOMISAKI GABBROIC COMPLEX

Abstract

The Murotomisaki differentiated gabbroic complex locates at the extreme point of the Cape Murotomisaki, Shikoku Island. This complex intruded into the Murotohanto Group of Eocene in age. The zonal arrangement of which complex shows the indication of the fractional crystallization with gravitational sinking. Principal rock types of the complex are as follows: chilled marginal dolerite, picrite gabbro, fine-grained hyperathene bearing olivine augite gabbro, medium-grained hyperathene bearing olivine augite gabbro, augite gabbro pegmatite and ferrogabbro. The pegmatitic rocks of the latest stage intruded as small veins. Anygrain of pigeonite or inverted pigeonite is not found, whereas a small amount of hypersthene is observable as internal precipitates. Iron concentration in olivine and in augite is conspicuous at the upper part of the complex. Ilmenite is the predominant opaque minerals through the course of fractionation and magnetite appears at the latest stage. Fractional crystallization of OLIVINE THOLEIITE to intermediate iron concentration under low vapour pressure and low oxygen partial pressure is studied on these bases.