Melt inclusion constraints on petrogenesis of the 2014–2015 Holuhraun eruption, Iceland

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 inclusionbearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H 2 O 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.

Integrated Petrological and Geophysical Constraints on Magma System Architecture in the Western Galápagos Archipelago: Insights From Wolf Volcano

“…These high P F liquids have a restricted range of MgO contents between 5.55 and 6.06 wt%, and do not include either the most MgO rich or poor glass analyses (Figure a). This does not preclude that these more primitive or evolved liquids were ternary saturated, as the statistical test can return false negatives (Hartley et al, ). However, the results with P F <0.8 are excluded to ensure the reliability of barometric results.…”

“…This calculates a probability factor for three‐phase saturation ( P F ), with the OPAM model returning reliable pressures at P F > 0.8. Although this filter falsely rejects a minority of multiply saturated liquids, it minimizes the OPAM uncertainty (Hartley et al, ). The standard error of estimate (SEE) has not been quantified for the Voigt et al () parameterization, and we therefore assume a conservative SEE equal to that of the original Yang et al () model (±1.4 kbar).…”

“…Geophysical and petrological constraints are not often combined to study the architecture of subvolcanic systems, largely because both data sets are seldom simultaneously available for the same eruptions (Jay et al, 2014). In the rare circumstance where both robust geophysical data sets and rock samples are available, integration can provide better constraints on magma storage depths, additional information about the structure and dynamics of magma plumbing systems, and an improved understanding of the processes responsible for pre-eruptive monitoring signals (Gudmundsson et al, 2016;Halldórsson et al, 2018;Hartley et al, 2018;Jay et al, 2014;Klügel et al, 2015;Laeger et al, 2017;Longpré et al, 2014;Magee et al, 2018;Stock et al, 2018).…”

A distinct metal fingerprint in arc volcanic emissions

“…top: emanation coefficient for metals and semi-metals from Holuhraun calculated by 6 by using a dilution factor calculated from their measurements of sulfur in vent and plume gases (x axis) versus emanation coefficient calculated in this study using the mass of sulfur outgassed from melt (from melt inclusion and matrix glass microanalysis 28 ) and X/SO 2 ratios in the plume)…”

“…Error propagated from gas measurements are in the range 10-20%. c Emanation coefficient calculated assuming the degassing of 1100 ppm sulfur, from 1500 ppm to 400 ppm 28 and using the X/SO 2 ratio of the plume to reconstruct the concentration of element X prior to degassing. 1,29 , which causes the emanation coefficients to be anomalously high when using the X/SO 2 ratio, combined with the melt inclusion sulfur contents, to reconstruct the metal contents of the melts (main paper, figure 2).…”