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    Eruption chemistry recorded by accretionary lapilli within pyroclastic density current deposits, Kilchrist, Isle of Skye, NW Scotland

    Brown, D. and Drake, Simon M. and Beard, Andy (2013) Eruption chemistry recorded by accretionary lapilli within pyroclastic density current deposits, Kilchrist, Isle of Skye, NW Scotland. In: Volcanic and Magmatic Studies Group Annual Meeting, 7th-9th January 2013, School of Earth Sciences, University of Bristol, Bristol, UK. (Unpublished)

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    Accretionary lapilli evolution remains controversial. Based on field, modelling and rare geochemical studies most workers argue for formation and growth within an eruption plume, although recent studies suggest formation within a pyroclastic density current. Here we adopt an integrated field and geochemical approach to test existing models of formation. A sequence of massive lapilli tuffs and breccias from the Isle of Skye, NW Scotland, record deposition from the sustained passage of a pyroclastic density current. Accretionary lapilli in two vertically chemically zoned massive lapilli tuff units within this sequence display evolving chemical trends from core to rim. The accretionary lapilli formed initially as basaltic ash pellets in a co-ignimbrite plume before falling under gravity into the underlying density current, where they accreted progressively more evolved laminae. These laminae record reverse tapping of a magma chamber with sequential pulses of basaltic andesite, andesite and dacite magma being fed into the density current. Accretion of laminae was initially supported by available moisture and turbulence, but growth ceased with the input of dacitic magma and drier conditions. The accretionary lapilli were formed within a sustained pyroclastic density current, which demonstrates that accretionary lapilli are not necessarily formed by simple fallout from an ash plume. Our model demonstrates that accretionary lapilli may be used to trace physical and chemical characteristics of complex eruptions, and understand the magmas which fed those eruptions.


    Item Type: Conference or Workshop Item (Poster)
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences
    Depositing User: Sarah Hall
    Date Deposited: 10 May 2016 14:46
    Last Modified: 02 Aug 2023 17:23


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