Ti-Magnetite Crystallization in Melt Inclusions of Trachytic Rocks from the Dokdo and Ulleung Islands, South Korea: Implications for Hydrous and Oxidized Magmatism

Inkyeong Moon,Hyunwoo Lee,Chang Hwan Kim,Jihye Oh,Donghoon Seoung,Jonguk Kim,Insung Lee,Chan Hong Park

doi:10.3390/min10070644

Abstract

The Dokdo and Ulleung islands (Korea) are volcanic islands in the East Sea (Sea of Japan), formed in the late Cenozoic. These volcanic islands, in the back-arc basin of the Japanese archipelago, provide important information about magma characteristics in the eastern margin of the Eurasian plate. The origin of the Dokdo and Ulleung intraplate volcanism is still controversial, and the role of fluids, especially water, in the magmatism is poorly understood. Here, we comprehensively analyzed the melt inclusions (10–100 m in diameter) hosted in clinopyroxene phenocrysts of trachyte, trachyandesite, and trachybasalt. In particular, we observed Ti-magnetite and amphibole which were crystallized as daughter mineral phases within melt inclusions, suggesting that Ti-magnetite was formed in an oxidized condition due to H2O dissociation and H2 diffusion. The Ti-magnetite exhibited compositional heterogeneities of MgO (average of 8.28 wt %), Al2O3 (average of 8.68 wt %), and TiO2 (average of 8.04 wt %). The positive correlation of TiO2 with Cr2O3 is probably attributed to evolutionary Fe–Ti-rich parent magma. Correspondingly, our results suggested hydrous and oxidized magmatism for the Dokdo and Ulleung volcanic islands.

Highlights

The Dokdo and Ulleung islands (DUI) are volcanoes located in the East Sea (Sea of Japan) that are a back-arc basin between the Korean peninsula and the Japanese arc, formed in the late Cenozoic (Figure 1a)
Submarine volcanic rocks were dredged by the East Sea Exploration (Onnuri R/V) for the Korea
Samples were collected near the Dokdo and Ulleung islands at depths of approximately 1000 m (Figure 1b,c)

Summary

Introduction

The Dokdo and Ulleung islands (DUI) are volcanoes located in the East Sea (Sea of Japan) that are a back-arc basin between the Korean peninsula and the Japanese arc, formed in the late Cenozoic (Figure 1a). The volcanic rocks of DUI provide an ideal opportunity to understand the evolved alkaline magmatism in the eastern margin of the Eurasian plate [1]. 1. (a) Geological map of the Dokdo and Ulleung islands (DUI) with the distribution of adjacent. Geological map of the Dokdo and Ulleung islands (DUI) with the distribution of adjacent plates (GeoMapApp 3.6.10). Contour maps of (b) Dokdo and (c) Ulleung generated using SURFER plates (GeoMapApp 3.6.10). Contour maps of (b) Dokdo (c) Ulleung generated using SURFER software.

Methods

Results

Discussion

Conclusion