Reconstructing the Magmatic and Volcanic Evolution of the Vesturdjúp Basin (Offshore Iceland) Using Reflection Seismic Imagery

Intraplate off-axis volcanism west of Iceland forms a volcanic province whose origin remains largely unexplored, despite extensive research on the nearby Reykjanes Ridge and onshore Iceland. Integrating 2950 km of multi-channel reflection seismic data with vertical gravity gradients, this study investigates the Vesturdjúp Basin (1000 – 2100 m water depth), where 43 volcanic edifices are preserved in the reflection seismic data. In the northern part of the basin, volcanic cones align along two perpendicular chains and a ridge-parallel lineament, while the southern part of the basin exhibits more dispersed volcanism.

Seismic facies analysis indicates a multi-stage magmatic evolution, shifting from early effusive flows to an explosive cone-building phase, before returning to effusive activity. Deep-water explosive volcanism is indicated by diatreme-like sub-surface geometries and outward-prograding flank reflections, interpreted as volcaniclastic aprons. Detailed seismostratigraphic reconstruction of representative edifices shows that construction progressed through repeated cycles of crater excavation and infill, accompanied by small-scale mass-transport deposits along the by oversteepened flanks.

Stratigraphic correlation suggests that volcanism was modulated by a pulsed magmatic regime. The timing of eruptive activity and intervening quiescence likely correlates with fluctuations in Iceland plume flux and regional tectonic reconfigurations. The spatial distribution of volcanic centres reflects the reactivation of inherited lithospheric weaknesses and rift-related discontinuities. These structural corridors may have provided pathways for plume-derived magma to ascend through the cooling off-axis lithosphere. Our results demonstrate how high-resolution seismic imaging can help to reconstruct the formation history of off-axis volcanism where structural inheritance and transient plume pulses overlap.