Petrology and geochemistry of the 2014-2015 Holuhraun eruption, central Iceland: compositional and mineralogical characteristics, temporal variability and magma storage

Saemundur A. Halldórsson, Enikő Bali, Margaret E. Hartley, David Neave, David W. Peate, Guðmundur H. Guðfinnsson, Ilya Bindeman, Martin J. Whitehouse, Morten S. Riishuus, Gro B. M. Pedersen, Sigurður Jakobsson, Rob Askew, Catherine R. Gallagher, Esther R. Guðmundsdóttir, Jónas Gudnason, William M. Moreland, Birgir V. Óskarsson, Paavo Nikkola, Hannah I. Reynolds, Johanne SchmithThorvaldur Thordarson

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    Abstract

    The 2014-2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a six-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra samples, mineral chemistry, and radiogenic and oxygen isotope analyses from an extensive set of samples (n=62) that were collected systematically in several field campaigns throughout the entire eruptive period. We also present the first detailed chemical and isotopic characterization of magmatic sulfides from Iceland. In conjunction with a unique set of geophysical data, our approach provides a detailed temporal and spatial resolution of magmatic processes before and during this eruption. The 2014-15 Holuhraun magma is compositionally indistinguishable from recent basalts erupted from the Bárðarbunga volcanic system, consistent with seismic observations for magma ascent close by the Bárðarbunga central volcano, followed by dyke propagation to the Holuhraun eruption site. Whole-rock elemental and isotopic compositions are remarkably constant throughout the eruption. Moreover, the inferred depth of the magma reservoir tapped during the eruption is consistently 8±5 km, in agreement with geodetic observations and melt inclusion entrapment pressures, but inconsistent with vertically extensive multi-tiered magma storage prior to eruption. The near constancy in the chemical and isotopic composition of the lava is consistent with efficient homogenization of mantle-derived compositional variability. In contrast, occurrence of different mineral populations, including sulfide globules, which display significant compositional variability, require a more complex pre-eruptive magmatic history. This may include sampling of heterogeneous mantle melts that mixed, crystallized and finally homogenized at mid- to lower-crustal conditions.
    Original languageEnglish
    JournalContributions to Mineralogy and Petrology
    Volume173
    Issue number64
    Early online date23 Jul 2018
    DOIs
    Publication statusPublished - Aug 2018

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