Spatio-temporal evolution of crystal-mush horizons in the Icelandic crust - A case study of the northern segment of the Bárdarbunga volcanic system

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Classical views of magma storage in melt-dominated single chambers have been increasingly challenged by petrological and geophysical studies over the past three decades. The concept of vertically extensive ‘magma columns’ consisting of an intricate network of interconnected, multi-level magma storage horizons (sills) embedded in partially solidified crystal-mush zones is now considered more realistic. Crystal-mush zones are dynamic bodies comprising a rheologically ‘stiffer’ framework of crystal-mush with interspersed melt lenses of variable shape and size; the proportion of crystal to melt fractions within crystal-mush zones varies in both space and time. Although the existence of crystal-mush zones in the crust beneath the Icelandic Axial Rift is supported by many lines of evidence, our understanding remains limited. Nevertheless, the implications of its existence for the rapid generation and mobilisation of magma are highly significant. In order to address the role of crystal-mush zones in volcanism in Iceland we focus on the following key questions. (1) What is the nature of magma storage? (2) What is the vertical extent of the storage network? (3) What is the mush zone made of and how does it process magma? (4) What are the timescales of magma storage, processing, and mobilization? We will investigate these questions using an integrated approach linking textural data with state-of-the-art quantitative petrological-geochemical methods and high-precision diffusion modelling. Our approach will be applied to a unique suite of temporally and geochemically well-constrained tholeiitic basalts from the northern segment of the highly-active Bárðarbunga fissure swarm, one of Iceland’s most productive and largest volcanic systems. This 3-year project offers a novel, quantitative assessment of the spatial and temporal evolution of magma storage, accumulation, remobilisation and transfer through crystal-mush zones one the scale of Bárðarbunga fissure swarm. The proposed study will provide key insights into to the thickness, structure, composition and physical state of the mid- to lower oceanic crust and will consolidate our understanding of crustal accretion and formation in an active spreading margin.