Abstract
The 2014–2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine–plagioclase–augite–melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1 ± 0.7 kbar (7.5 ± 2.5 km), which is in agreement with the depths of earthquakes (6 ± 1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1–12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12–0.29 m s−1. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions.
Highlights
The recent eruption at Holuhraun within the Bárðarbunga volcanic system in central Iceland began on August 2014 and, with the exception of a short break in activity on August, continued until 27 February 2015, producing over 1.4 km3 of dominantly plagioclase–phyric lava and tephra
Major element compositions of melt inclusions can be greatly affected by post-entrapment crystallization (PEC) of the host mineral onto the inclusion walls
For olivine-hosted inclusions, PEC causes a reduction in melt inclusion Mg#; for plagioclase-hosted inclusions, Mg# is unaffected, but A l2O3 and CaO are removed from the inclusion by PEC
Summary
The recent eruption at Holuhraun within the Bárðarbunga volcanic system in central Iceland began on August 2014 and, with the exception of a short break in activity on August, continued until 27 February 2015, producing over 1.4 km of dominantly plagioclase–phyric lava and tephra. We present a detailed petrological and geochemical characterization of erupted products from Holuhraun We use these data to evaluate pressures of melt mixing, storage,. We compare our petrological observations with geophysical data to evaluate the fidelity of petrological and geochemical datasets in recovering the apparent magma storage and transport during a major volcano-tectonic episode. For the first time, we have recovered petrological constraints on melt storage and transport pressures that are in very good agreement with seismic and geodetic determinations from the same event. This marks a significant step forward towards the reconciliation of petrological and geophysical datasets. Our methods and results are applicable to the interpretation of melt transport pathways during historical eruptions where geophysical and geodetic data are not available, and may lead to significant improvements in the forecasting of future fissure eruptions, both in Iceland and further afield
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