Skip to content

Origin of Silicic Magmatism at the Katla Volcanic Complex, South Iceland

Valentin R. Troll1,2, Frances M. Deegan1,2, Jussi S. Heinonen3,4, Caroline Svanholm1, Chris Harris5,  Christian M. Lacasse6, Harri Geiger7, Agata Poganj1, Malin Andersson1, Romain Meyer8, Thorvaldur Thordarson9

  • Affiliations: 1Uppsala University, Dept. of Earth Sciences, Natural Resources & Sustainable Development, Uppsala, Sweden; 2Centre for Natural Hazards and Disaster Science (CNDS), Uppsala University, Sweden; 3Åbo Akademi University, Geology and Mineralogy, Åbo, Finland; 4University of Helsinki, Department of Geoscience and Geography, Helsinki, Finland; 5University of Cape Town, Department of Geological Sciences, South Africa; 6SQN 412, Bloco M, Apt. 105, Asa Norte, CEP: 70867-130, Brasília, DF, Brazil; 7Institute of Earth and Environmental Sciences, University of Freiburg, Freiburg im Breisgau, Germany; 8Service géologique du Luxembourg, Bertrange, Luxembourg; 9University of Iceland, Faculty of Earth Sciences, Iceland 

  • Presentation type: Talk

  • Presentation time: Thursday 16:15 - 16:30, Room S150

  • Programme No: 1.9.7

  • Theme 1 > Session 9

Abstract

The Katla volcano is a bimodal caldera complex within Iceland's basalt-dominated Eastern Volcanic Zone. To unravel the petrogenesis of silica-rich rocks from Katla, we provide new δ18O values for almost 60 basaltic, intermediate, and high-silica eruptive rocks, including a number of partially melted felsic xenoliths. The basaltic samples display a range in bulk-rock δ18O values from +4.3 to +8.5‰ (n=17) and the sparse intermediate samples from +4.1 to +5.9‰ (n=3). In turn, silicic rock samples and feldspar separates range from +2.7 to +6.4‰ (n=38), whereas the felsic xenoliths yield the lowest values from -4.9 to -2.3‰ (n=4). The majority (95%) of the Katla silicic volcanics have δ18O values below typical MORB (ie. ≤ 5.0‰), ruling out an origin via closed-system fractional crystallisation from the basaltic magmas. We utilised the new δ18O values to model possible assimilation and fractional crystallisation (AFC) scenarios. The results indicate an early stage of FC/AFC at deep- to mid-crustal levels, followed by assimilation of low-δ18O hydrothermally-altered sub-volcanic materials similar to the low-δ18O felsic xenoliths at shallow crustal levels. Such a two-stage magma evolution is consistent with available geophysical and geobarometry studies at Katla, indicating mid- to deep-crustal as well as shallow-crustal magma domains. Importantly, mafic rocks show dominantly MORB-like δ18O values, whereas low δ18O values occur essentially in silicic rocks only. This implies that the low-δ18O values at Katla are imposed by interaction with Icelandic crust, rather than reflecting low δ18O in the underlying mantle sources.