Remobilization of silicic intrusion by mafic magmas during the 2010 Eyjafjallajökull eruption

Abstract

Abstract. Injection of basaltic magmas into silicic crustal holding chambers and subsequent magma mingling or mixing is a process that has been recognised since the late seventies as resulting in explosive eruptions. Detailed reconstruction and assessment of the mixing process caused by such intrusion is now possible because of the exceptional time-sequence sample suite available from the tephra fallout of the 2010 summit eruption at Eyjafjallajökull volcano in South Iceland. Fallout from 14 to 19 April contains three glass types of basaltic, intermediate, and silicic compositions recording rapid magma mingling without homogenisation, involving evolved FeTi-basalt and silicic melt with composition identical to that produced by the 1821-1823 AD Eyjafjallajökull summit eruption. The time-dependent change in the magma composition suggests a binary mixing process with changing end-member compositions and proportions. Beginning of May, a new injection of primitive basalt was recorded by deep seismicity, appearance of Mgrich olivine phenocrysts together with high sulphur dioxide output and presence of sulphide crystals. Thus, the composition of the basaltic injection became more magnesian and hotter with time provoking changes in the silicic mixing end-member from pre-existing melt to the solid carapace of the magma chamber. Finally, decreasing proportions of the mafic end-member with time in the erupted mixedmagma demonstrate that injections of Mg-rich basalt was the motor of the 2010 Eyjafjallajökull explosive eruption, andCorrespondence to: O. Sigmarsson (olgeir@raunvis.hi.is) that its decreasing inflow terminated the eruption. Significant quantity of silicic magma is thus still present in the interior of the volcano. Our results show that detailed sampling during the entire eruption was essential for deciphering the complex magmatic processes at play, i.e. the dynamics of the magma mingling and mixing. Finally, the rapid compositional changes in the eruptive products suggest that magma mingling occurs on a timescale of a few hours to days whereas the interval between the first detected magma injection and eruption was several months.

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

“…However, the low ( 210 Pb/ 226 Ra) ratios cannot be explained by the mixing process advocated above between a residing silicic magma and basalt similar to FH2. It is possible that the increased influx of basalt, in early May 2010, into the Eyjafjallajökull plumbing system induced a melting of a solidified part of the silicic magma chamber as proposed by Sigmarsson et al (2011). The resulting silicic melt would be in 226 Ra-210 Pb-210 Po radioactive equilibrium and its mingling with the basaltic magma would indeed give magmas with ( 210 Pb/ 226 Ra) ratios lower than 1.…”

“…4; Sigmarsson et al, 2011;Tarasewicz et al, 2012 and references therein). The tephra erupted in May 2010 record a different magmatic history.…”

“…The U Sigmarsson et al, 2011) and has 12.1 ppm of Th relative to A-THO. The Th-isotope ratios were analysed by multi-collector inductively coupled mass spectrometry on a Neptune Plus TM instrument.…”

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

“…where it is described in detail. Sigmarsson et al 2122. analyzed a separate fraction of this sample.…”

Fingerprints of magma mingling processes within the Miocene Zebín tuff cone feeding system (Jičín Volcanic Field, Czech Republic)

“…The basic input, having a higher solidus temperature than the trachyandesite differentiates, remobilized the system and induced eruption of the mingled dikes. Such reactivation of silicic magma by intrusion of basaltic melt was observed also during recent volcanic eruptions including Ilopango Tierra Blanca Jóven (TBJ; Richer et al 2004), Pinatubo 1991 (Pallister et al 1992), and Eyjafjallajökull 2010 (Sigmundsson et al 2010;Sigmarsson et al 2011). On the other hand, mingling of compositionally highly contrasting magmas underneath monogenetic volcanoes is rather scarce (Schreiber et al 1999), especially during the course of the eruption.…”