Flow direction and internal structure of Seaward Dipping Reflectors along the Mid-Norwegian Volcanic Margin

The Mid-Norwegian margin hosts a thick volcanic succession of break-up–related basalts forming the seaward-dipping reflectors (SDRs). We investigated the magnetic fabric of basalts sampled from the feather edge of inner SDR packages. Azimuthally unoriented samples were collected during International Ocean Drilling Program (IODP) Expedition 396, from three sites along the margin from Kolga High in the south to the Skoll High in the north. Rock magnetic characterization suggests the presence of pseudo-singe domain Ti-magnetite as the main remanence carrier in the basalt. Our results show that the AMS in SDR basalt primarily reflects distribution anisotropy arising from subhedral/euhedral Ti-magnetite grains enclosed within an early-formed silicate framework.

The direction of natural remanent magnetization (NRM) preserved in the basalts is used to reorient the specimens into their in-situ orientation, allowing interpretation of the AMS fabric in a geographic coordinate system. Reoriented magnetic fabrics show systematic alignment with independent flow indicators.

Individual lava flows exhibit a strong zonation of magnetic fabric, characterized by oppositely dipping foliations in the top and basal parts. The opposing pair of foliations is attributed to flow-induced shear strain that is effective in the distal parts, away from the eruption centre, once a semi-solid / solid upper crust is developed. Imbricated magnetic foliations developed at the base of individual flows are used to decipher the lava flow direction, which indicates a consistently landward-directed lava transport towards the south. AMS-derived flow directions are also supported by seismic images, which show subvertical dyke swarms at the seaward edge of the inner SDR in the north, that likely served as feeders to the thick basaltic succession.