Hiroshi Asai

Some basic schistose rocks at the midstream of Horoman river in the southern Hidaka metamorphic province, Hokkaido

The writer presents some considerations on the genesis of some basic schistose rocks in the southern Hidaka metamorphic province.The basic schistose rocks described here are the schistose-plagioclase amphibolite (fine grained rock), the plagioclase amphibolite (medium grained rock) and the hornblende-plagioclase gneiss (coarse grained rock). It is concluded that most of the fine or medium grained basic schistose rocks are originated from the biotite rich hornfelsic rocks and the coarse grained basic schistose rocks are from the coarse biotite rich quartz-biotite-plagioclase rocks. The former two are products at the earlier stage of metamorphism and the latter is a product at the later stage of metamorphism in this district.

The tonalite and its associated fine-grained basic in the southern part of Okushibetsu district, Hokkaido

The tonalite and the fine-grained basic rocks occur in the southern part of Okushibetsu district, Hokkaido. The tonalites are the cummingtonite tonalite and the kalifeldspar bearing hypersthene cummingtonite tonalite. The finegrained basic rocks are the biotite bearing hypersthene brown hornblende plagioclase rock, the biotite bearing hypersthene quartz plagioclase pale brown hornblende rock, the green hornblende plagioclase rock, and the quartz biotite plagioclase brown hornblende rock.Judging from the observations of these rocks under the microscope, they are of the metamorphic origins which came from the biotite rich coarse rock or the biotite rich hornfelsic rock.