A History of Andesite Production via Magma Mixing and Mingling Revealed Microscopically at Ngauruhoe Volcano

Many andesites erupted at arc volcanoes are the products of magma mixing, and this process could be important in triggering their eruption. Throughout life Ngauruhoe volcano (?2.5 ka), lack macroscopic enclaves or lithological features mingled magma. However, intricate microscopic mixing mingling occur. Plagioclase phenocrysts have a wide range textures. Their diverse 87Sr/86Sr values (0.7039–0.7060) mostly discordant with groundmass (?80%), many (>40%) isotopically zoned. Resorbed calcic cores overgrown by sodic rims common, record gradient increasing 87Sr/86Sr, result progressive radiogenic melt. Clinopyroxenes orthopyroxenes relict that nucleated silicic melts (?Mg# 30–40), cycles growth mafic 50–60). Olivine-bearing, glassy blebs (mostly <500 ?m) occur relicts intruding disintegrated during mixing/mingling process, liberated crystals. Thus, some banding fact product thorough contrasting magmas. This may require regime frequent intrusion leading to hybridization stagnant resident eruptions Ngauruhoe's historic episode ending 1975 CE likely been manifestation replenishment. A origin for intermediate rocks volcanic arcs is more prevalent than previously documented: further evidence rarity andesite liquids such settings.