Geothermobarometry of the 2010 Eyjafjallajökull eruption: New constraints on Icelandic magma plumbing systems

Abstract

[1] The 2010 Eyjafjallajökull eruption in Iceland produced mildly alkaline basalt that was emitted during the initial flank eruptive phase, whereas tephra predominately of benmorite composition was erupted during the second explosive phase from the summit of the volcano. These latter magmas show pervasive magma mingling between basalts and silicic magma. Glass and coexisting equilibrium mineral analyses have been used to define pressure-temperature crystallization paths for the eruption based on melt, clinopyroxene-melt and plagioclase-melt thermobarometry. Temperature calculations show that the early basaltic eruptions from the flank eruption have magmatic temperatures of around 1170 C (AE25 C) and a narrow temperature range (<30 C) at any given depth. In contrast, benmoritic products crystallized at lower temperatures (1000-1060 C). Pressure estimates yield an average pressure of 5.6-6.4 kbar (AE1.5 kbar) for the basaltic tephra and variable but lower pressures for the benmoritic samples ranging down to 0.6 kbar. The mafic magma mainly crystallized in the deeper crust (16-18 km), whereas mingled magma from the summit eruption crystallized at more shallow crustal levels (2-5 km) suggesting multistage magma ascent. Magmatic water concentrations were estimated with plagioclase-melt hygrometry. The maximum average water content of 1.8 wt % H 2 O, obtained in one of the summit samples, is in agreement with melt inclusion observations. Water concentration of this or lower levels is demonstrated to only have limited effect on the pressure-temperature calculations.

Excess 210 Po in 2010 Eyjafjallajökull tephra (Iceland): Evidence for pre-eruptive gas accumulation

“…The benmoreite (samples EJ-1, -2A and -5) and the trachyte produced during the very last phase of the Eyjafjallajökull eruption (samples EJ-6 and -7) have U-Th systematics within the range of Iceland's silicic rocks (e.g. Condomines et al, 1981;Sigmarsson et al, 1991Sigmarsson et al, , 1992Zellmer et al, 2008;Kuritani et al, 2011). As in the Vestmannaeyjar rock series, the ( 226 Ra/ 230 Th) of the Fimmvörðuhálsls-Eyjafjallajökull basalt-benmoreite-trachyte suite decreases with increasing Th concentrations (Fig.…”

210Pb-226Ra disequilibria in young gas-laden magmas

“…Portions of Iceland offer a physical setting where such magma stagnation and differentiation is common because of its rather water rich parental magmas, glaciation, thicker and somewhat older crust70. The benmoreite from Eyjafjallajökull appears to have stagnated at a depth in the crust of about 1.7–5.0 km71 without persistent Rn degassing as evidenced by its equilibrium ( 210 Pb/ 226 Ra) ratio.…”

Mass eruption rates in pulsating eruptions estimated from video analysis of the gas thrust-buoyancy transition—a case study of the 2010 eruption of Eyjafjallajökull, Iceland

“…Considering a magmatic gas mass fraction of 2 % at the source level (Borisova et al 2012;Keiding and Sigmarsson 2012), the mass ratio between solids and gas of roughly 2:1 found at the transitional level implies that at this stage, the primary magmatic gas component constitutes only about~1.3 % of the gas phase. This means that the dominant component of the gas phase is entrained air, which exceeds the amount of magmatic gas by a factor of more than 20.…”

“…A temperature drop of the plume from 1000-1170°C at the source (Keiding and Sigmarsson 2012) to 480°C at the transitional level in combination with a magmatic gas mass fraction of approximately 2 % (Borisova et al 2012;Keiding and Sigmarsson 2012) would indicate that at the zone of transition, a large fraction of the gas must have contained entrained air. Thus, with PVDM, we used for ρ g -as a firstorder approximation-a density of 0.39 kg/m 3 , corresponding to the density of 480°C hot air at atmospheric pressure (using 1550 m a.s.l.…”