Petrologic Study on the Busan Migmatitic Gneiss in the northeastern Margin of the Ogcheon Zone

옥천대(沃川帶) 북동변(北東邊)에 분포(分布)하는 부산혼성편마암(婦山混成片麻岩)에 대(對)한 암석학적(岩石學的) 연구(硏究)

Busan migmatitic gneisses in the northeastern margin of the Ogcheon zone have been studied petrologically in order to clarify their origin. Petrochemical and mineralogical studies show that the gneisses are Precambrian basemental paragneisses and the rocks were migmatized more intensively than the Bagdalryeong gneisses which have been known to constitute the basemental gneisses of Ogcheon zone. K-Ar biotite isotopic ages are $150.79{\pm}3.37Ma$ in Busan migmatitic gneiss and $191{\pm}4.27Ma$ in Bagdalryeong gneisses. These ages seem to be isotopic homogenised ages. Progressive regional metamorphisms are predominent in the studied area showing greenschist facies, epidote amphibolite facies and amphibolite facies toward N-W direction.