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The production of large volumes of silicic magma in predominantly basaltic crust: Slaufrudalur pluton and the hidden volcanoes of Hornafjörður

Robert Alexander Askew 1,2; Steffi Burchardt3; Sæmundur Ari Halldórsson1; Catherine Rachael Gallagher1; Olivier Bachmann4; Razvan-Gabriel Popa4; Krístján Jónasson2

  • Affiliations: 1University of Iceland, Institute of Earth Sciences, Sturlugata 7, 102 Reykjavík, Iceland; 2Natural Science Institute of Iceland, Urriðaholt 6-8, Garðabær, Iceland; 3University of Uppsala, Department of Earth Sciences, Villavägen 16, 752 36 Uppsala, Sweden; 4ETH Zürich, Inst. für Geochemie und Petrologie, NW E 88.2, Clausiusstrasse 25, 8092 Zürich, Switzerland

  • Presentation type: Poster

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

  • Poster Board Number: 208

  • Programme No: 1.9.15

  • Theme 1 > Session 9

Abstract

The generation of large volumes of silicic magma in basalt-dominated crust remains a topic of ongoing debate. Previous models (AFC vs. crustal melting) focus on the chemical processes only and largely ignore the mechanics of silicic magma production. To better understand the interplay between these processes, we study the Slaufrudalur pluton, the largest silicic pluton in Iceland (~8--10 km³) and its surroundings. Despite previous studies investigating the pluton composition and emplacement, its existence within Iceland's basaltic crust has long been puzzling. Our new geological mapping, age data, and geochemical analyses from the Slaufrudalur region provide fresh insights into this problem. We identified several silicic central volcanoes hosting the pluton, and zircon ages from these silicic volcanics are the same, or younger than, zircons ages within the pluton. This indicates zircon recycling and suggests that the generation of this silicic magma was largely driven by the recycling of older silicic material from buried central volcanoes. Additionally, the spatial alignment of central volcanoes surrounding the pluton suggests its emplacement was strongly controlled by pre-existing structures. To further contextualize our findings, we also present geochemical data on plutons and volcanoes in the wider SE-Iceland area, highlighting the larger scale geodynamics at play. These findings allow us to present a temporal and spatial model for the production of large volumes of silicic magma in Iceland. Our results quantify the efficiency, speed, and structural controls of silicic magma generation and crustal recycling, shedding light on a key process in Icelandic magmatic systems.