In situ observation of nanolite formation in volcanic melt: implications for magma explosive volcanism
Danilo Di GenovaJames W. E. DrewittRichard A. BrookerSimone AnzelliniH. M. MaderLouis HennetDaniel R. NeuvilleA. Longo
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The volatile content in magmas is fundamental for the triggering and style of volcanic eruptions. Carbon dioxide, the second most abundant volatile component in magmas after H2O, is the first to reach saturation upon ascent and depressurization. We investigate experimentally CO2-bubble nucleation in trachybasalt and trachyte melts at high temperature and high pressure (HT and HP) through wetting-angle measurements on different (sialic, mafic or oxide) phenocryst phases. The presence of crystals lowers the supersaturation required for CO2-bubble nucleation up to 37 per cent (heterogeneous nucleation, HeN), with a minor role of mineral chemistry. Different from H2O-rich systems, feldspar crystals are effective in reducing required supersaturation for bubble nucleation. Our data suggest that leucite, the dominant liquidus phase in ultrapotassic systems at shallow depth (i.e. <100 MPa), facilitates late-stage, extensive magma vesiculation through CO2HeN, which may explain the shifting of CO2-rich eruptive systems towards an apparently anomalous explosive behaviour.
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Melt inclusions
Volcanic Gases
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Caldera
Silicic
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