Quaternary Magmatism in NW Svalbard: Refining the Architecture and Evolution of Sverrefjellet Volcano

Sverrefjellet is the remnant of an extinct alkali basaltic stratovolcano located in NW Svalbard, representing a distinctive phase of Quaternary magmatism in the High Arctic. It is part of the Bockfjorden Volcanic Complex, which consists of several eruption centers within the Woodfjorden-Bockfjorden area. The volcanism occurred during the northern hemisphere’s glaciations and reveals evidence for magma interactions with glaciers. The Quaternary eruption centers are localized along the Breibogen Fault and were probably linked to the evolution of the Knipovich mid-oceanic ridge, yet the exact age of the magmatic activity remains uncertain. Sverrefjellet is renowned for its high abundance of mantle-derived xenoliths, which have become a focal point in most publications on this volcano to date. However, the magmatic architecture and physical volcanology of Sverrefjellet have received only limited attention after the initial mapping by Skjelkvåle et al. (1989).

In July 2023, an international multi-disciplinary geoscientific expedition to Woodfjorden-Bockfjorden was undertaken. One of the primary objectives was to perform detailed mapping and systematic sampling of volcanic-related units within Sverrefjellet volcano, with the aim of exploring and refining magma emplacement processes. To facilitate this, drones were utilized to acquire high-resolution 3D digital textured models over the best-exposed outcrops of the volcano. The in-field sampling of the main volcanic units was accompanied by extensive (∼100) magnetic susceptibility measurements with a hand-held Kappameter (SM-30). In total, 20 rock samples have been prepared for petrographic, SEM and EPMA analyses.

We observed the presence of mantle-derived xenoliths in all volcanic units, which include dyke intrusions, pillow basalts with associated lava tubes, basaltic lava flows, and various volcanogenic sediments. The slopes of the extinct volcano display predominant frost weathering, with the southern slope adorned with olivine sand and gravel sourced from 'bomb-shaped' nodules or clasts that typically contain peridotite xenoliths as their cores. The presence of pillow lavas and associated 1 to 2 meter large lava tubes suggests subglacial magma emplacement. This is supported by their relatively high elevation at 200-300 meters above sea-level, which makes interaction with seawater highly unlikely.

In between lava flows and dykes, texturally distinctive zones characterized by platy tops and bottoms as well as numerous flattened boulder-sized xenolithic nodules were observed. Petrographic and SEM analyses of xenoliths and host basalts revealed no preferred alignment of crystals within the platy zones, suggesting that these schistose textures developed due to rapid magma cooling and subsequent freeze-thaw action rather than tectonic shearing. The basalts display typical ferrimagnetic susceptibilities (average: 3.24 × 10^-3 SI), whereas the volcanogenic sediments exhibit low paramagnetic susceptibility (0.38 × 10^-3 SI), indicating rapid magma quenching during fragmentation, which is characteristic of subglacial emplacement.

Our preliminary results support a subglacial origin for the Sverrefjellet eruptions. Ongoing detailed mapping and thorough magnetic mineralogy analyses, coupled with geochronological and geomorphological studies, will enhance our understanding of subglacial volcanic processes at the extinct Sverrefjellet volcano and more broadly. Additionally, these findings will contribute to a better understanding of the nature and origin of High Arctic Quaternary magmatism and its paleogeographic setting.