Petrologic Study on the so-called Schistose Granites in the northeastern part of the Kwangju

광주(光州) 북동부(北東部)에 분포(分布)하는 소위(所謂) 편상화강암(片狀花崗岩)에 관(關)한 암석학적(岩石學的) 연구(硏究)

This studg is to clarify intrusion sequence and petrogenetic processes of the so-called schistose granites in the northeastheastern part of the Kwangju, Chonnam Province. The study area is composed of the Pre-cambrian and Unknown age metasediments, the Unknown age schistose granites and basic plutons, the Cretaceous sedimentary and volcanic rocks, and the Cretaceous Ogang-ri granite and dykes. The schistose granites of the study area is divided into three rock units based on relative intrusion age, mineralogical constituent and texture;SoonChang schistose granite, two mica granite and Sam-o-ri schistose granite. The schistose granites intruded into metasediments, are intruded by Ogang-ri granite and dikes, and overlain by the Cretaceous sedimentary and volcanic rocks. The schistose granites vary widely in composition (granite-granodiorite-tonalite) and content of porphyroblastic feldspar Caugen and rectangular shaped). The foliation of schistose granites shows similar trend to the Shinian direction. In especially, strong foliation reflects dynamic metamorphism by mortar texture and much content of well oriented biotite. These schistose granites are characterized by its gray feldspar porphyroblasts. This feldspar is considered to be formed by potassic metasomatism and assimilation of pelitic metasediments of unexposed highly metamorphosed rocks deeply buried under the level of the schistose granites emplacement. Variation of silica versus oxides of major elements shows that the schistose granites are similar to the trend of Daly's average basalt-andesite-dacite-rhyolite which shows the trend of the fractional crystallization of magma. AMF diagram shows that the schistose granite is corresponded to contaminated differentiation products such as Lower California batholith and Cascade lava. These evidence suggest that the schistose granite is a series of differentiation products formed by fractional crystallization that associated with srtongly contamination and potassic metasomatism.