Olivine gabbro, olivine norite in the vicinity of Horoman river in Southern Hidaka metamorphic zone (I)

Abstract

Olivine gabbro, brown hornblende-olivine gabbro, melaorthopyroxene-olivine gabbro, brown hornblende-olivine gabbro and olivine bearing-brown hornblende-clinopyroxene norite, which have the coarse idiomorphic or hypidiomorphic granular texture or sometimes have the coarse metablastic ophitic texture, occur in micro or medium grained granular basic rocks which are orthopyroxene-plagioclase-brown hornblende amphibolite, glomelo-porphyroblast-orthopyroxene-brown hornblende plagioclase rock, brown hornblende norite, brown hornblende-clinopyroxene norite and olivine porphyroblast-brown hornblende gabbro. Judging from the careful observations in the field and under the microscope, the writer observes the facts that the phenomena of the concentration and the dispersion of brown hornblende occur in the country basic rocks or even in olivine gabbro and olivine norite, and that in these rocks the metablastic orthopyroxene or clinopyroxene or even olivine crystallize in the place of early crystallized unstable mafic minerals and that the phenomena of clouding, cleaning and basification of plagioclase occur in these rocks. The progressive ultra-metamorphism which originates olivine gabbro or olivine norite, happens at the heigher stage of metamorphism in this district.