Application of the MELTS program to the fractional crystallization of low-alumina alkaline magma on Jeju Volcanic Island, Korea

Abstract Jeju Volcanic Island is the largest island in South Korea and is considered a continental shelf intraplate volcanic island. In this study, MELTS, a powerful program for modeling magmatic evolution processes, was applied to simulate the fractional crystallization process of the low-alumina alkaline volcanic rock suite on Jeju Island. MELTS modeling was conducted at many isobaric pressures ranging from 2.0 GPa to 0.1 GPa, different oxygen fugacities (fO 2 ) from FMQ-3 to FMQ + 3, and different H 2 O contents. The results demonstrate that the most suitable fractionation model for the Jeju low-alumina alkaline magma involves a pressure of 0.2 GPa to 0.1 GPa and an oxygen fugacity close to the FMQ buffer. Additionally, an H 2 O content of 0.5 wt.% is the most consistent with the evolution trend and mineral composition of the natural rock suite on Jeju Island. Although MELTS possesses several limitations in terms of the stability of calibration, such as spinel overestimation and a lack of experiments on hydrous minerals (which should be improved), MELTS performs well in terms of temperature and pressure prediction and in terms of the assessment of other factors of the fractional crystallization process on Jeju Island. Consequently, to evaluate a magmatic process in a particular region, MELTS should be combined with other analyses and not relied upon independently.