Sakurajima volcano on the rim of Aira caldera erupts daily, threatening the major nearby population centre of Kagoshima. Before 1955, eruptions have typically consisted of intermittent Plinian and effusive activity, but since 1955, frequent Vulcanian explosions have occurred, indicating a change in pre-eruptive processes. High-resolution Pb isotopes are used here to constrain the components, including crustal assimilants, and petrogenetic processes contributing to the composition of both pre and post 1955 magmas. Sakurajima eruptive products have more radiogenic Pb (206Pb/204Pb = 18.40–18.42) than nearby Sumiyoshiike basalts (206Pb/204Pb = 18.24), a proxy for the primitive magma feeding the Sakurajima-Aira system. Sakurajima samples lie along a mixing line between these basalts and locally exposed crustal compositions. Their Pb isotopes are consistent with addition of ~ 5% average crustal melt to the primitive basaltic magma. The narrow range of Pb isotope ratios, despite variable SiO2 contents (56.6–72.3 wt%), suggests that the final erupted magmas are derived from fractional crystallization of a mafic precursory magma displaying relatively consistent levels of crustal contamination. Andesites erupted between 4–3.7 ka and the 1995 eruption are contaminated to a greater extent, indicating that magmas with distinct compositions can feed phases of activity or individual eruptions. Post 1955 andesitic pyroclastics have lower SiO2 and higher MgO than older lavas, yet equivalent Pb isotope ratios. The more mafic composition of post 1955 eruptive products can be attributed to increased throughput of mafic magma to the system.

中文翻译：

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使用高分辨率铅同位素解开日本樱岛火山的岩石成因

位于爱良火山口边缘的樱岛火山每天都在喷发，威胁着附近的主要人口中心鹿儿岛。1955 年之前，火山喷发通常由间歇性普林尼式和喷发性活动组成，但自 1955 年以来，火山爆发频繁发生，表明喷发前过程发生了变化。此处使用高分辨率 Pb 同位素来限制成分，包括地壳同化物，以及对 1955 年前后岩浆成分有贡献的成岩过程。樱岛喷发产物的放射性铅 (206Pb/204Pb = 18.40–18.42) 比附近的住吉池玄武岩 (206Pb/204Pb = 18.24) 多，这是为樱岛-爱拉系统提供原始岩浆的代表。樱岛样本位于这些玄武岩和局部暴露的地壳成分之间的混合线上。它们的 Pb 同位素与原始玄武质岩浆中添加约 5% 的平均地壳熔体一致。尽管 SiO2 含量可变（56.6-72.3 wt%），但 Pb 同位素比率的范围很窄，这表明最终喷发的岩浆来自显示相对一致的地壳污染水平的镁铁质前体岩浆的分步结晶。在 4-3.7 ka 和 1995 年喷发之间喷发的安山岩受到更大程度的污染，这表明具有不同成分的岩浆可以为活动阶段或个别喷发提供营养。1955 年后的安山岩火山碎屑比旧熔岩具有更低的 SiO2 和更高的 MgO，但具有相同的 Pb 同位素比率。1955 年后喷发产物的更多基性成分可归因于系统中基性岩浆的吞吐量增加。