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首页> 外文期刊>Earth, planets and space: EPS >Mafic-felsic magma interaction at Satsuma-Iwojima volcano, Japan: Evidence from mafic inclusions in rhyolites
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Mafic-felsic magma interaction at Satsuma-Iwojima volcano, Japan: Evidence from mafic inclusions in rhyolites

机译：日本萨摩-岩岛火山的镁铁质-长质岩浆相互作用：流纹岩中镁铁质包裹体的证据

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Geochemical and petrographic studies of the rhyolites and mafic inclusions from Satsuma-Iwojima volcano were carried out in order to investigate evolution of a silicic, bimodal magma system during the post-caldera stage. Abundant mafic inclusions, which are fine-grained with vesicles in their cores, are present in the Showa-Iwojima rhyolitic lava. Inclusions with similar textures are found in Iwodake volcanic bombs but are less common than in the Showa-Iwojima lava. The major and trace element compositions of the inclusions plot along mixing lines connecting the host rhyolites with spatially and temporally associated basaltic to basaltic andesite magmas. Plagioclase phenocrysts in the inclusions have a large variation in core compositions (An42 to An96), and exhibit various zoning profiles and reaction textures, indicating they coexisted with melts ranging from basaltic to rhyolitic composition. Pyroxenes also exhibit a wide range in composition and a variety of zoning patterns consistent with multiple sources. These results suggest that a stratified magma chamber exists beneath the volcano, consisting of a lower basaltic layer, an upper rhyolitic layer and an episodically-present, thin middle layer of andesite. Variations in the chemistry of the Iwodake and Showa-Iwojima mafic inclusions suggest that multiple injections of very similar basaltic magma have occurred since the growth of the Iwodake dome. More extensive textural disequilibrium shows that the Showa-Iwojima rhyolites formed through more extensive interaction with mafic magma. The mafic-felsic interaction is consistent with degassing model of a magma chamber estimated by other researchers, which consists of degassing of upper rhyolitic magma by convection in a conduit and supply of a CO2-rich volatile phase from underlying basaltic magma to the rhyolitic magma.
机译：为了研究火山灰后阶段的硅质，双峰岩浆系统的演化，对萨摩-岩岛火山的流纹岩和镁铁质包裹体进行了地球化学和岩石学研究。昭和-岩岛流纹岩熔岩中存在丰富的镁铁质包裹体，这些包裹体的核心是细小颗粒。在岩岳岳火山炸弹中发现了具有相似纹理的夹杂物，但与昭和岩-岛熔岩相比并不常见。夹杂物的主要和微量元素组成沿混合线绘制，这些混合线将主流纹岩与时空相关的玄武岩与玄武安山岩岩浆连接。夹杂物中斜长石的面晶在核心组成上有很大的变化（An 42 至An 96 ），并表现出各种分区分布和反应质地，表明它们与熔体共存。玄武质至流纹岩成分。辉石也表现出广泛的组成和与多种来源一致的各种分区模式。这些结果表明，火山下面存在一个分层的岩浆室，由下部玄武岩层，上部流纹岩层和安山岩中存在的稀薄的中间薄层组成。岩岳和昭和岩岛镁铁质包裹体的化学变化表明，自岩岳穹顶生长以来，已经发生了多次非常相似的玄武岩浆注入。更加广泛的质地不平衡表明，昭和岩岛流纹岩是通过与镁铁质岩浆的更广泛相互作用而形成的。镁铁质-长质质相互作用与其他研究人员估计的岩浆室脱气模型一致，该模型包括通过在导管中对流对上流质岩浆进行脱气，并从中供应富含CO 2 的挥发性相。玄武质岩浆到流纹岩浆。

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