Chemical composition of glass inclusions of volcanic rocks from the Bonin Arc@en

The chemical composition of glass inclusions in phenocrystic plagioclase and pyroxene from Sites 792 and 793, drilled during Ocean Drilling Program Leg 126 in the Bonin Arc, is examined. Immiscible liquid, which is preserved as glass inclusions with unmixed textures in plagioclase, is observed in a high-magnesian andesite, which suggests an important role of liquid immiscibility in the fractionation of high-magnesian andesite. In other andesitic rocks (SiO2 = 57-60 wt%), such unmixed textures of glass inclusions in calcic plagioclase with a similar percentage of An (around 80%) is not found. The degree of fractionation and mixing of liquid are inferred from the glass composition in pyroxene.本研究针对博宁弧（Bonin Arc）大洋钻探计划（Ocean Drilling Program）第126航次钻探获取的792、793站位样品，分析了其中斑晶斜长石（phenocrystic plagioclase）与辉石（pyroxene）内的玻璃包裹体（glass inclusions）化学成分。在一件高镁安山岩（high-magnesian andesite）样品中，观察到以具分相结构（unmixed textures）的玻璃包裹体形式留存的不混溶流体（immiscible liquid），该现象表明流体不混溶作用在高镁安山岩的岩浆分异过程中扮演了关键角色。在SiO₂含量为57~60 wt%的其他安山岩样品中，并未发现钙长石组分（An）占比约为80%的钙斜长石（calcic plagioclase）内存在此类玻璃包裹体分相结构。可通过辉石中的玻璃包裹体化学成分，推断岩浆流体的分异与混合程度。