抄録
The original magma of the Murotomisaki gabbroic complex is characterized by undersaturation with silica (SiO2=47.4wt%), low Al2O3 (15.4), low total alkalis (Na2O+K2O=2.5), low TiO2 (1.0), and also with comparatively high iron content (FeO+Fe2O3=13.5). Increase of silica content through the course of fractionation is not found, while iron enrichment in the residual liquid is conspicuous. From these petrochemical features, the original magma of the Murotomisaki complex is concluded to be a kind of OLIVINE THOLEIITE BASALT MAGMA and a model for the fractionation with gravitational sinking is proposed.
