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<title lang=en>Excess Po-210 in 2010 Eyjatjallajokull tephra (Iceland): Evidence for pre-eruptive gas accumulation</title>
<creator>Sigmarsson, Olgeir</creator>
<creator>Condomines, Michel</creator>
<creator>Gauthier, Pierre-Jean</creator>
<contributor>Laboratoire Magmas et Volcans (LMV) ; Université Blaise Pascal - Clermont-Ferrand 2 (UBP) - Institut national des sciences de l'Univers (INSU - CNRS) - Université Jean Monnet [Saint-Étienne] (UJM) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<contributor>Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<contributor>Risques ; Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) - Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<description>International audience</description>
<source>ISSN: 0012-821X</source>
<source>Earth and Planetary Science Letters</source>
<publisher>Elsevier</publisher>
<identifier>hal-01217142</identifier>
<identifier>https://hal.archives-ouvertes.fr/hal-01217142</identifier>
<source>https://hal.archives-ouvertes.fr/hal-01217142</source>
<source>Earth and Planetary Science Letters, Elsevier, 2015, 427, pp.66-73. 〈10.1016/j.epsl.2015.06.054〉</source>
<identifier>DOI : 10.1016/j.epsl.2015.06.054</identifier>
<relation>info:eu-repo/semantics/altIdentifier/doi/10.1016/j.epsl.2015.06.054</relation>
<language>en</language>
<subject lang=en>polonium</subject>
<subject lang=en>radon degassing</subject>
<subject lang=en>accumulation in magmas</subject>
<subject lang=en>Po-210-Pb-210-Ra-226 disequilibria</subject>
<subject lang=en>free vapour phase</subject>
<subject lang=en>closed-open system degassing</subject>
<subject lang=en>Eyjafjallajokull volcano</subject>
<subject>[SDU.STU.GC] Sciences of the Universe [physics]/Earth Sciences/Geochemistry</subject>
<type>info:eu-repo/semantics/article</type>
<type>Journal articles</type>
<description lang=en>Excess gas phase in magmas erupting explosively is well known worldwide. However, the origin of this gas phase, in excess of what can be dissolved in the erupting magma at depth, and the rate of gas accumulation is less well defined. The 2010 mildly explosive eruption at Eyjafjallajökull, Iceland, produced mingled tephra of benmoreitic and trachytic composition whereas alkali basalt was emitted during preceding flank eruption. Tephra of the first explosive phase are composed of three glass types, alkaline rhyolite, mixed benmoreite, and basalt, which suggests that the basaltic magma intruded a pre-existing rhyolitic magma chamber, and ultimately triggered the eruption. The mixed benmoreitic tephra (erupted on 15 and 17 April 2010) had large 210Po in excess of 210Pb View the MathML source[(Po210/Pb210)0=1.88] at the time of eruption, and possibly a small 210Pb excess over its parent 226Ra. In contrast, the preceding flank eruption produced basalt with View the MathML source(Po210)0=0, upon eruption, and the final trachyte had lost most of its 210Po during open-system degassing. The 210Po excess in the first erupted benmoreites is interpreted to result from 210Po degassing of basaltic magma and the accumulation of 210Po-enriched gas, either in the upper part of the basaltic intrusion, below the rhyolite–basalt interface, or in the pre-existing residual rhyolitic magma chamber. From a simple model of radon and polonium accumulation in the rhyolitic reservoir, the ratio of the mass of basalt magma degassing over the mass of magma accumulating the excess gas decreased from 20 to 15 over 2 days, implying zoned magma reservoir, with the uppermost and gas-richest part erupting first. The duration of pre-eruptive gas accumulation in this model is approximately one year. This corresponds closely to the initiation of a seismic swarm beneath Eyjafjallajökull, early June 2009, which was the first pre-eruptive signal detected. The coincidence between initiation of gas accumulation at relatively shallow depth and deeper seismicity strongly suggests that the excess gas phase originated from a basalt magma batch intruded at depth, and that this gas phase reached the surface approximately a year later.</description>
<date>2015-10-01</date>
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