하동-산청 사장암복합체의 관입시기와 마그마 분화과정에 대한 연구

Abstract

Hadong-Sancheong Anorthosite Complex is distributed in the Yeongnam Massif in South Korea. These are tectonically correlated with Jirisan gneiss complex and charnockite. In order to determine their magma differentiatation process and the intrusive ages, anorthosite, layer-type leucogabbro, intercumulate-type leucogabbro and gabbro from Hadong-Sancheong Anorthosite Complex have been chosen for a comparative study regarding their rock chemistry, mineral chemistry and age dating. Hadong-Sancheong Anorthosite Complex mainly consists of plagioclase and amphibole. Pyroxeneis are observed as relict minerals in recrystallized amphibole by secondary alteration and metamorphism. The An compositional variation of internal plagioclase is uniform. Despite the difference of location, mafic mineral content and characteristic textures, plagioclases have nearly similar An content. The anorthositic rocks are generally rich in Al2O3, CaO and Na2O, reflecting high amounts of cumulus plagioclase. Variations in trace and rare earth elemental abundances show typical magmatic differentiation trends. On a chondrite-normalized REE diagram, Hadong-Sancheong anorthosite complex displays significant LREE-enrichment and positive Eu anomalies. The anorthositic magma was differentiated from anorthosite– leucogabbro–gabbro-Fe-Ti rich leucogabbro. The crystallization age of the anorthositic magmatism was confirmed by U-Pb age determination on the zircon from intercumulate-type leucogabbro (SC-4) and gabbro (GPS639-1). Intercumulate-type leucogabbro contains igneous zircon cores that yield Proterozoic formation ages of 1855±7.8Ma and metamorphic rims around zircons that yield 1837±7.5Ma. It is suggested that Hadong-Sancheong Anorthosite Complex suffered from high-temperature granulite facies metamorphism.