Spatio-temporal evolution of crystal-mush horizons in the Icelandic crust - A case study of the northern segment of the Bárdarbunga volcanic system
Final Report Abstract
The aim of this 3-year project was to investigate the spatial and temporal evolution of magma storage, accumulation, remobilisation and transfer through crystal-mush zones on the scale of a single volcanic system in Iceland. This was achieved through an integrated research approach that linked textural data with state-of-the-art quantitative petrological-geochemical methods and high-precision diffusion modelling applied to an exceptional suite of late-stage sub-glacial (Gígöldur and Hrímalda) and historical (~1382 AD Fjallsendahraun) tholeiitic basalts from the northern segment of the highly active Bárðarbunga volcanic system located in the Eastern Volcanic Zone in central Iceland. Combined with existing geochemical and petrological data from the southern segment, this dataset will enable us to reconstruct changes in magma storage conditions and timescales of magma mobilisation over time and space in one of Iceland’s largest and most active volcanic systems. The project is not yet complete and was delayed due to unforeseen circumstances. To date, we have conducted in-situ microanalysis on 1107 groundmass glasses, 411 melt inclusions, and 290 macrocrysts (olivine n=179; clinopyroxene n=76; plagioclase n=35). Macrocrysts from the oldest units (late-stage subglacial) are the most primitive, and their compositional range widens and becomes more evolved over time. Macrocryst rims are in chemical equilibrium with their respective carrier melts, while the cores of the macrocrysts are too primitive to have crystallized from these melts. This suggests a possible crystal-mush origin. Preliminary clinopyroxene-melt and melt-based (OPAM) geobarometers indicate crystallization pressures of 1.4±0.8 and 1.8±0.7 kbar, corresponding to depths of 5.0-6.4km. These results are consistent with mid-crustal magma storage depth constrained for other eruptions within the Bárðarbunga volcanic system. Oxygen isotope compositions were measured in groundmass glasses, olivine-hosted melt inclusions and host-olivines to compare with pre-existing δ18O values for samples from the southern segment. The aim was to assess how and where crustal rocks interact with ascending magmas in the igneous system. SIMS δ18O values of groundmass glasses (GG) range from +2.77 to +5.08 ‰, while melt inclusions (MIs) have values between +3.19 and +4.86 ‰. The majority of MIs (80%) record δ18O values >+4.0‰, but only 54% of the GGs have δ18O values >+4.0‰. Laser fluorination bulk data of GGs are in good agreement with SIMS data. Host olivines record δ18O values within the range +2.65 to +4.48‰. Assessing the extent of oxygen exchange with the Icelandic crust and constraining timescales of magma mobilisation and mush disaggregation for the sample suites from the southern segment of the Bárðarbunga volcanic system is currently a work in progress.
Publications
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Temporal evolution of magma and crystal mush storage conditions in the Bárðarbunga-Veiðivötn volcanic system, Iceland. Lithos, 352-353, 105234.
Caracciolo, Alberto; Bali, Enikő; Guðfinnsson, Guðmundur H.; Kahl, Maren; Halldórsson, Sæmundur A.; Hartley, Margaret E. & Gunnarsson, Haraldur
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Timescales of crystal mush mobilization in the Bárðarbunga-Veiðivötn volcanic system based on olivine diffusion chronometry. Am. Min., in press.
Caracciolo, A., Kahl, M., Bali, E., Guðfinnsson, G.H., Halldórsson, S.A. & Hartley, M.E.
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Deep magma mobilization years before the 2021 CE Fagradalsfjall eruption, Iceland. Geology, 51(2), 184-188.
Kahl, M.; Mutch, E.J.F.; Maclennan, J.; Morgan, D.J.; Couperthwaite, F.; Bali, E.; Thordarson, T.; Guðfinnsson, G.H.; Walshaw, R.; Buisman, I.; Buhre, S.; van der Meer, Q.H.A.; Caracciolo, A.; Marshall, E.W.; Rasmussen, M.B.; Gallagher, C.R.; Moreland, W.M.; Höskuldsson, Á. & Askew, R.A.
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Linking diffusion chronometry to geophysical indicators of volcanic unrest – Insights from the 2021 Fagradalsfjall eruption. Hybrid Goldschmidt 2022, Hawaii, USA. (oral)
Kahl, M.
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Oxygen isotope evidence for progressively assimilating trans-crustal magma plumbing systems in Iceland. Geology, 50(7), 796-800.
Caracciolo, A.; Halldórsson, S.A.; Bali, E.; Marshall, E.W.; Jeon, H.; Whitehouse, M.J.; Barnes, J.D.; Guðfinnsson, G.H.; Kahl, M. & Hartley, M.E.
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Years of deep magmatic upheaval preceding the 2021 eruption at Fagradalsfjall, Iceland. EGU General Assembly, Vienna, Austria. Solicited speaker
Kahl, M.
