The effects of magma plumbing system processes on the crystal cargo; a geochemical, textural and numerical modelling approach

Camilla Imarisio

Research output: ThesisDoctoral Thesis

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The products of volcanic eruptions are the final result of a variety of processes such as fractional crystallisation, magma mixing and crustal assimilation. It is one of the challenges of modern volcanology to unravel the history of these products to better understand magma plumbing systems underlying volcanic centres and provide a strong basis for volcanic hazard assessment. Magmatic crystals, and plagioclase in particular, record information on the environment in which they grew in and hence zoned crystals store a detailed history of the conditions they have been stored in and the processes that have occurred, unfortunately due to complex mineral-melt relationships and complex crystallisation dynamics, these processes are difficult to quantify. For this thesis, a range of geochemical analyses has been used to investigate the chemical composition of volcanic rocks and crystals. Coupled with extensive macro and micro-textural petrological observations, these have been used to study the plumbing system of two volcanic centres in a plume centred rift zone and a subduction zone setting. The two centres differ from one another in terms of geodynamic setting, dominating magmatic open system processes, eruptive style, and erupted product composition and petrological characteristics. As well as providing the basis for investigating the full extent and differences of the effects of magmatic processes on the crystal cargo in rift versus volcanic arc settings, this also provided the opportunity to investigate the extent and dynamics of magmatic open system processes at these volcanic centres, where whole rock studies had so far been dominant.
Torfajökull is the largest silicic centre in Iceland and its last two historic eruptions, 871AD and 1477, have erupted simultaneously with the Veiðivötn fissure. The products of these eruptions provide a petrological and geochemical insight into magma mixing between basaltic and rhyolitic melts as well as mush entrainment processes. Volcanic chronometers, such as diffusion modification, have been used to model the timescales of these processes and have shown very quick mixing/entrainment to eruption times, on the scale of days, suggesting a strong link between melt interaction and eruption triggering. Magmatic processes and their extent can vary drastically between volcanic centres. To provide a comparison, lavas from Salina, Aeolian Islands, were sampled, where whole rock studies of intermediate lavas have been interpreted as the products of fractional crystallisation and crustal assimilation processes, common in volcanic arcs. The crystal cargoes hosted in these products provide an insight into the effects of magmatic recharge, crustal assimilation, prolonged crustal storage and high water contents on crystal cargo chemistry, as well differences in plumbing system structure and evolution.
The data acquired from both volcanic systems is used to develop and test CrystalMath, a new numerical model developed which aims to forward model the evolution of a magma and its olivine - clinopyroxene - plagioclase crystalline assemblage. The model outputs the geochemical evolution of the melt and that of each crystal, and a 3D thin section like image providing a visual representation of the zoned crystals and the overall texture of the "rock". This forward model can be used to test and better quantify a range of crystallisation parameters and magmatic processes and their effects on the crystal cargo, using natural samples as a tie point.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Manning, Christina, Supervisor
Award date1 Oct 2019
Publication statusUnpublished - 2019

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