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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Mechanisms of oxidation and degassing in the Takanoobane rhyolite lava of Aso Volcano, Japan
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Mechanisms of oxidation and degassing in the Takanoobane rhyolite lava of Aso Volcano, Japan

机译：日本阿苏火山高野坝流纹岩熔岩中的氧化和脱气机理

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Vertical variation of the oxidation state as recorded by Fe-Ti oxides of Takanoobane rhyolite lava (TR lava) is revealed on the basis of petrographic and rock magnetic studies. Petrographic observations of the interior of TR lava showed that Fe-Ti oxides are preferentially oxidized along the flow structure that is characterized by the light-colored band composed of aggregates of deformed minute cavities, whereas both the top and bottom parts of the lava are not oxidized. Rock magnetic studies measuring thermal demagnetization of a three-component isothermal remanent magnetization (IRM) and magnetic susceptibility revealed that hematite of a highly oxidized state is formed preferentially along the light-colored band, consistent with the petrographic observations. The observed preferential oxidation of the light-colored band is adequately explained by post-eruptive degassing of hydrogen from the interior of the lava, rather than migration of atmospheric oxygen into the hot interior of the cooling lava against the back-streaming volcanic gas. The magmatic volatiles emitted from the interior can be transported effectively through the light-colored band and microcracks which ubiquitously develop nearly vertical to the flow direction. The degassing mechanism should be limited to highly viscous silicic lavas such as rhyolite because the mechanism requires development of the flow structure and the microcracks as the pathways for gases. These structures are achieved only in highly viscous silicic lavas.
机译：高岭土流纹岩熔岩（TR熔岩）的铁钛氧化物记录的氧化态的垂直变化是在岩石学和岩石磁学研究的基础上揭示的。对TR熔岩内部的岩石学观察表明，Fe-Ti氧化物沿流动结构优先被氧化，该流动结构的特征是由变形的微小空腔聚集体组成的浅色带，而熔岩的顶部和底部均未被氧化。岩石磁学研究测量了三组分等温剩余磁化强度（IRM）的热退磁和磁化率，结果表明，高度氧化态的赤铁矿优先沿着浅色带形成，这与岩石学观测一致。通过从熔岩内部对氢进行喷发后脱气，而不是将大气中的氧气逆流回返火山气体，将其迁移到冷却熔岩的热内部，可以充分解释观察到的浅色带的优先氧化。从内部散发出来的岩浆挥发物可以有效地通过浅色带和微裂纹传输，这些裂纹和微裂纹普遍沿垂直于流动方向发展。脱气机理应仅限于高粘性硅质熔岩（如流纹岩），因为该机理需要发展流动结构和微裂纹作为气体通道。这些结构只有在高粘性硅质熔岩中才能实现。

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