The gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs. Hence, clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir. Recent experimental studies have determined the gas permeabilities in crystal-free rhyolite and basalt. However, no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas. In this study, we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol% to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation. Size-controlled (100-meshed) corundum crystals were used as an analog of the phenocrysts in silicic magmas. Microstructural analyses using X-ray CT showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression, that is, an increase in the vesicularity. As long as the vesicularities of melt part in the crystal-free basis (melt vesicularity) were similar, no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities <68 vol%. The corundum showed a large contact angle with aqueous fluid as well as plagioclase and alkaline feldspar; this failed to induce the efficient heterogeneous nucleation and coalescence of bubbles on its surface. The gas permeabilities of all the run products were lower than the detection limits of the present analysis (the order of 10−16 m2) at melt vesicularities 68 vol%). This result indicates that the permeable fluid transport through a deep volcanic conduit, which has been proposed on the basis of the observations of volcanic gases and natural products, is so slow that other processes, like shear deformation or magma convection, may be needed to explain the observations.
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机译：岩浆中的气体和流体通过相互连接的气泡网络的渗透流传输，控制了火山岩在火山管道中上升的放气速率以及岩浆储层的糊状边界层中的流体传输。因此，弄清其机制和速率对于了解火山喷发的爆炸性以及岩浆储层的演化和动力学至关重要。最近的实验研究确定了无晶体流纹岩和玄武岩中的气体渗透率。然而，没有实验研究调查晶体含量对岩浆中可渗透气体传输的影响。在这项研究中，我们对结晶度分别为30和50％（体积）的含水流纹岩熔体进行了减压实验，以研究晶体对岩浆囊泡化过程中气泡微观结构和气体渗透性的影响。尺寸受控（100目）的刚玉晶体被用作硅质岩浆中隐晶晶的类似物。使用X射线CT进行的微结构分析表明，气泡聚结并且其连通性随着减压后最终压力的降低（即，囊泡性的提高）而增加。只要以无晶体为基础的熔融部分的囊泡度（熔体囊泡度）相似，则在小于68vol％的熔体囊泡度下，未观察到结晶度对气泡聚结程度和连通性的明显影响。刚玉与水性液体以及斜长石和碱性长石的接触角大。这未能在其表面上引起气泡的有效异质形核和聚结。所有运行产物的气体渗透率均低于当前分析的检出限（10 −16 m 2 的溶出度为68 vol％）。该结果表明，根据火山岩气和天然产物的观测结果提出的通过深层火山管道的渗透性流体传输非常缓慢，以至于可能需要用其他过程（如剪切变形或岩浆对流）来解释。观察。
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