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Hydrogen (δD), oxygen (δ18O) and noble gas characterization of volcanics in the Hofsjökull volcanic area (Iceland): implications for magmatic degassing in sub- vs. post-glacial eruptions

Genki Ichikawa1, Antonio M. Álvarez-Valero1 , Antonio Caracausi2, Sæmundur A. Halldórsson3, Anika Tullos4, Antonio Polo Sánchez1, Javier Borrajo5, Masao Ban6, Hirochika Sumino7, Ray Burgess8

  • Affiliations: 1Departamento de Geología, Universidad de Salamanca, Salamanca, Spain; 2Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy; 3University of Iceland, Reykjavik, Iceland;4University of Oregon, Eugene, USA; 5Departamento de Ciencias Biomédicas y del Diagnóstico, Universidad de Salamanca, Salamanca, Spain; 6Department of Science, Yamagata University, Yamagata, Japan; 7Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan; 8Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 173

  • Programme No: 3.3.11

  • Theme 3 > Session 3

Abstract

Geochemistry of volatiles in active volcanoes provides insights into the magmatic processes at depth, such as magma evolution and degassing, which can be implemented into volcanic hazards assessment. Polar magmatic systems in Iceland represent excellent natural laboratories with numerous historical and current volcanic activity. Hydrogen, oxygen and noble gas isotopic variations in volatiles trapped in igneous rocks (subglacial glass and/or mafic crystals) of the Hofsjökull volcano provide essential information on past mechanisms controlling the eruptive history (sub- and/or post-glacial) of this large volcano with potential implications for other glacial volcanoes worldwide. Hydrogen and oxygen isotope ratios reveal (i) plausible "ice-age" water contribution in the sub-glacial samples, and (ii) shifting degassing conditions from closed sub-glacial stage to open degassing system in the interglacial stages, which might be due to the decreasing glacier load. Helium isotope data reveal higher affinity to a plume origin than a MORB for its magma source (3He/4He up to 23.8 Ra), whereas the 4He-40Ar* abundance systematics of the sub-glacial glasses are inconsistent with extensive degassing possibly due to the glacial loading above the volcanic plumbing system. Integrated petrologic features infer fast magma cooling in both sub- and post-glacial samples and different chamber(s) depths.