Volcanic gas emission is considered to reflect the degassing of magma beneath volcanoes. The combined observations of gas measurement and petrological study are expected to constrain the volatile concentrations and storage depths of the pre-eruptive and primitive magma. Aso volcano (Japan) is a constantly-monitored, persistently-degassing volcano, and an ideal site to acquire gas and petrologic data. We analyzed the melt inclusions and phenocryst minerals of Holocene basaltic eruption products, and reported their major and volatile element concentrations. The samples showed abundant evidence of magma mixing, such as reverse mineral zoning, and highly variable mineral and glass compositions. SiO 2 measured in melt inclusions varied from 46.0–65.8 wt. %. High-volatile concentration, S up to 3750 ppm, was only found in mafic melt inclusions hosted by high-Fo olivine phenocrysts (~ Fo82). The pre-eruptive storage depths were determined from volatile concentrations: 2 and 4 km depth for Strombolian eruption and sub-Plinian eruption, respectively. The volatile-rich primitive magma, one end member of the mixed-magma, originated from a deeper level (> 10 km) than these magma reservoirs. Initial volatile concentrations of the primitive magma were determined using multiple constraints: > 4.68 wt. % H 2 O, 400—750 ppm CO 2 , 3750 ppm S, 716 ppm Cl, and 324 ppm F. The observed variation of volcanic gas composition was best explained by the mixing of the gas segregated from at least a depth of 10 km, with that from the shallow reservoirs. This study illustrated the method to identify the primitive mafic magma responsible for deep volatile flux in a mature volcano with complex magmatic processes.

中文翻译：

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源自活火山深部玄武质岩浆库的持续性气体排放：以日本阿苏火山为例

火山气体排放被认为反映了火山下岩浆的脱气。气体测量和岩石学研究的联合观测预计将限制喷发前和原始岩浆的挥发物浓度和储存深度。阿苏火山（日本）是一座持续监测、持续脱气的火山，是获取天然气和岩石学数据的理想地点。我们分析了全新世玄武岩喷发产物的熔体包裹体和斑晶矿物，并报告了它们的主要和挥发性元素浓度。样品显示了大量岩浆混合的证据，例如反向矿物分带，以及高度可变的矿物和玻璃成分。在熔体夹杂物中测得的 SiO 2 为 46.0-65.8 wt。%。高挥发浓度，S 高达 3750 ppm，仅在由高 Fo 橄榄石斑晶 (~ Fo82) 承载的镁铁质熔体包裹体中发现。喷发前储存深度由挥发物浓度确定：Strombolian 喷发和 sub-Plinian 喷发分别为 2 和 4 公里深度。富含挥发分的原始岩浆是混合岩浆的一个末端成员，起源于比这些岩浆储层更深的水平（> 10 km）。原始岩浆的初始挥发性浓度是使用多个约束条件确定的：> 4.68 wt。% H 2 O、400-750 ppm CO 2 、3750 ppm S、716 ppm Cl 和 324 ppm F。 观察到的火山气体成分的变化最好通过从至少 10 公里深度分离的气体混合来解释，从浅水库。