Geochemical Characterization of Intraplate Magmatism from Quaternary Alkaline Volcanic Rocks on Jeju Island, South Korea

The major and trace elements of Quaternary alkaline volcanic rocks on Jeju Island were analyzed to determine their origin and formation mechanism. The samples included tephrite, trachybasalts, basaltic trachyandesites, tephriphonolites, trachytes, and mantle xenoliths in the host basalt. Although the samples exhibited diversity in SiO2 contents, the relations of Zr vs. Nb and La vs. Nb indicated that the rocks were formed from the fractional crystallization of a single parent magma with slight continental crustal contamination (r: 0–0.3 by AFC modeling), rather than by the mixing of different magma sources. The volcanic rocks had an enriched-mantle-2-like ocean island basalt signature and the basalt was formed by partial melting of the upper mantle, represented by the xenolith samples of our study. The upper mantle of Jeju was affected by arc magmatism, associated with the subduction of the Pacific Plate beneath the Eurasian Plate. Therefore, we inferred that two separate magmatic events occurred on Jeju Island: one associated with the subduction of the Pacific Plate beneath the Eurasian Plate (represented by xenoliths), and another associated with a divergent setting when intraplate magmatism occurred (represented by the host rocks). With AFC modeling, it can be proposed that the Jeju volcanic rocks were formed by the fractional crystallization of the upper mantle combined with assimilation of the continental crust. The xenoliths in this study had different geochemical patterns from previously reported xenoliths, warranting further investigations.