TRANSITION FROM CALC-ALKALIC TO ADAKITIC MAGMATISM AT THE NAMHAE ISLAND, SOUTH KOREA

The Namhae Island located within lower part of the Gyeongsang basin of the southeastern part of the Korean Peninsula. I-type calc-alkaline series of igneous rocks with age of Cretaceous to Tertiary intruded to the Mesozoic sediments of the Gyeongsang basin. These intrusive rocks are possibly the result of intensive magmatism which occurred in response to the subduction of the Izanagi Plate beneath the northeastern part of the Eurasian Plate. According to the previous study, the Jindong granitoids adjacent to the Namhae districts have reported adakitic evidences. It has reported that the intrusive rocks of study area are micrographic granitic rock and granodiorite in composition. In the variation diagrams, the overall geochemical features of the granitoids from Namhae districts show systematic variations in major and trace elements. In the tectonic discrimination diagrams, the granitoids from Namhae districts are originated from volcanic arc environment. These rocks show higher SiO₂, Al₂O₃, Na₂O, MgO, Sr, Sr/Y, and low Y contents compared with typical calc-alkaline granitic rocks. Also chondrite normalized REE (rare earth elements) patterns are typically for adakitic signature without negative Eu anomaly. However, La/Yb and La/Y ratios and Yb contents are slightly deviated adakitic field. These differences seem to be associated with contamination with continental crust during the evolution of intruded magma.