Petrographical study on the Yucheon granite and its enclaves

Abstract

The Yucheon granite in the central Gyeongsang basin composed of fine grained equigranular granite, medium grained equigranular granite, and porphyritic granite, and contains enclaves. The enclaves are classified into microenclave, mafic microgranular enclave, and hybrid zone by their size. They show various features formed by magma mixing/mingling environment: abundant subrounded shape, sharp but partly diffuse contact with host granite, crenulated surface, equigranular texture, finer grain size than host granites, rapakivi feldspar, phenocrysts in enclaves from granite, more mafic small enclave in large enclave, ocellar and ovoid texture, poikilitic quartz and alkali feldspar, chilled rim, etc. Very fine-grained equigranular texture these enclaves, except phenocryst from granite, reflects that mafic magma was in near liquidus state when it was injected into granitic magma. Complete mixing was not achieved in hybrid zone because of very shallow level intrusion, high thermal contrast, and abundant phenocrysts with net veining of granitic materials. These phenocrysts triggered rapid crystallization of mafic magma.