Magmatic degassing in contrasting volcanic systems of the Vanuatu arc: constraints from uranium-series isotopes

Heather Handley, Simon Turner, Mark Reagan, Guillaume Girard, Shane Cronin

    Research output: Contribution to journalMeeting abstract

    Abstract

    Recent and present volcanism in the Vanuatu arc (South West Pacific Ocean) occurs at a variety of volcano types that exhibit a wide range of eruptive behaviour: from post-caldera lava-lake activity and lava flows at shield volcanoes (Ambrym), moderately explosive sub-plinian events and associated pyroclastic-flows and lava flows at stratovolcanoes (Lopevi), to persistent strombolian and vulcanian-style eruptions at scoria cones (Yasur). This precludes a generic model of magmatic and eruptive behaviour for the Vantuatu arc volcanoes and necessitates a detailed study of each system. Uranium-series disequilibria in volcanic rocks offer unique insights into pre-eruptive magmatic systems over process-relevant timescales e.g., ²³⁸U-²³⁰Th (380 Ka), ²³⁰Th-²²⁶Ra (8 Ka) and ²²⁶Ra-²¹⁰Pb (100 a). The short half-life of ²¹⁰Pb (t½ = 22.6 years) and the volatile nature of the intermediate isotope, ²²²Rn, (intermediate between the ²²⁶Ra parent and ²¹⁰Pb daughter) provide valuable information on magma transport, evolution and degassing over a timescale more pertinent to the processes leading up to volcanic eruptions. We present new Uranium-series isotope data (U-Th-Ra-²¹⁰Pb) for young ( 1) in the most mafic samples suggesting that ²²²Rn gas accumulation and fluxing preceding and/or during eruption (on a decadal timescale) may be responsible for the more explosive-style of eruption witnessed at this volcano. Significant accumulation of recently crystallised plagioclase phenocrysts can also create ²¹⁰Pb excesses in volcanic rocks, however, this process is not supported by the petrographic and geochemical data. In summary ²¹⁰Pb-²²⁶Ra disequilibria in Vanuatu volcanic rocks reveal a strong link between pre-eruptive magma degassing systematics and the resultant style of volcanic activity.
    Original languageEnglish
    Pages (from-to)1804
    Number of pages1
    JournalMineralogical Magazine
    Volume76
    Issue number6
    Publication statusPublished - 2012
    EventGoldschmidt Conference (22nd : 2012) - Montreal, Canada
    Duration: 24 Jun 201229 Jun 2012

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