Deep crustal melt plumbing of Bárðarbunga volcano, Iceland

Abstract

Understanding magmatic plumbing within the Earth's crust is important for understanding volcanic systems and improving eruption forecasting. We discuss magma plumbing under Bárðarbunga volcano, Iceland, over a 4 year period encompassing the largest Icelandic eruption in 230 years. Microseismicity extends through the usually ductile region of the Earth's crust, from 7 to 22 km depth in a subvertical column. Moment tensor solutions for an example earthquake exhibits opening tensile crack behavior. This is consistent with the deep (>7 km) seismicity being caused by the movement of melt in the normally aseismic crust. The seismically inferred melt path from the mantle source is offset laterally from the center of the Bárðarbunga caldera by ~12 km, rather than lying directly beneath it. It is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera.

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

“…This implies that their host macrocrysts crystallized and trapped their inclusions at deeper levels in the crust, and were transported into the Bárðarbunga magma reservoir prior to the onset of seismicity on 16 August 2014. The occurrence of deep (12-25 km) earthquakes in the area east of Bárðarbunga over the 4 years preceding the Holuhraun eruption (Vogfjörð et al 2015;Hudson et al 2017) could be consistent with magma supply from depth to a reservoir 8-12 km beneath Bárðarbunga (Fig. 11b).…”

What Drives the Lateral Versus Vertical Propagation of Dikes? Insights From Analogue Models

“…Indeed, considering that the density of silicate melts ranges from 2,200 to 2,800 kg/m 3 (Bottinga & Weill, ; Murase & McBirney, ) and the density of crustal rocks ranges from 1,600 to 3,100 kg/m 3 (Turcotte & Schubert, ), we obtain that Δ ρ spans from −1,200 to 900 kg/m 3 . Excluding extreme values, typical density contrast in recent diking events span from −300 to +300 kg/m 3 as for El Hierro 2011–2012 (Figure S9a; Martí et al, , ; Fullea et al, ), Bardarbunga 2014–2015 (Figure S9b; M. T. Gudmundsson & Hognadottir, ; Haddadi et al, ; Hudson et al, ), and Kilauea (Ryan, ; Zucca et al, ). In case of such negative density contrasts (i.e., a less buoyant magma) the dike stable height is relatively low (1–2 km; Townsend et al, ), suggesting that the dikes were vertically trapped at high depths and propagated laterally for tens of kilometers before erupting.…”

Melt movement through the Icelandic crust

“…Indeed, it is likely that melt also ponds as lenses in the upper mantle and in the crust-mantle transition zone. This sub-vertical column of seismicity was active several years before the 2014-2015 Bardarbunga-Holuhraun eruption and has continued subsequently to the present day, with little change in the frequency of earthquakes [13]. So this vertical melt feeder does not appear to be related directly to the onset of the dyke propagation discussed below.…”

“…One of the clearest examples is the deep sub-vertical column of crustal seismicity on the southeastern flank of the Bárðarbunga caldera shown in figure 2. The deep seismicity, and hence melt plumbing, occurs primarily at depths of 7-22 km [13]. The lack of recorded seismicity below 22 km does not mean there is no melt transport there, because melt must travel up from its source in the mantle below this depth.…”

“…Bárðarbunga's main magma storage region is thought to be at 5-12 km depth bsl [49,50]. However, Ágústsdóttir [51] and Hudson et al [13] find only a handful of events deeper than 8 km under the caldera.…”