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 μm 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.

中文翻译：

---

来自韩国独岛和宇隆群岛的疏松岩熔体夹杂物中的钛磁铁矿结晶：对含水量和氧化岩浆作用的影响

独岛和Ulleung岛（韩国）是东海（日本海）的火山岛，形成于新生代晚期。这些位于日本群岛后弧盆地的火山岛提供了有关欧亚板块东缘岩浆特征的重要信息。独岛和Ulleung板内火山活动的起源仍存在争议，并且对流体，尤其是水在岩浆作用中的作用还知之甚少。在这里，我们全面分析了曲奇，斜方锰矿和曲奇玄武岩的斜辉石型隐晶中所含的熔体包裹体（直径为10-100μm）。特别是，我们观察到钛磁铁矿和角闪石在熔融夹杂物中结晶为子矿相，这表明钛磁铁矿是在H ₂的氧化条件下形成的O解离和H ₂扩散。Ti磁铁矿表现出MgO（平均为8.28重量％），Al ₂ O ₃（平均为8.68重量％）和TiO ₂（平均为8.04重量％）的组成异质性。TiO ₂与Cr ₂ O ₃的正相关性可能归因于富Fe-Ti演化的母岩浆。相应地，我们的结果表明独岛和Ulleung火山岛的含水和氧化岩浆作用。