Magmatic domes and the initiation of oceanic processes at the Mid-Norwegian rifted margin

The transition from continental rifting to oceanic accretion - and the related initiation of the spreading ridge - remains one of the least understood phases in plate tectonics. This study presents new seismic reflection observations from the Møre and Vøring margins offshore Norway, revealing a series of deep dome-like structures in the outer rifted domain. These features, identified across multiple profiles, are interpreted as crystallized magmatic bodies - possibly gabbroic sills or lenses -emplaced during the rift-to-drift transition. The domes are associated with high seismic reflectivity and velocity, and spatially correlate with the boundary between sills and lava flows, suggesting a strong magmatic control.

It is proposed that these domes represent proto-magma chambers or magma mush zones, potentially marking early, stuttering attempts at ridge initiation. Their alignment sub-parallel to the continent-ocean boundary (COB) implies a broader magmatic axis at the margin scale. These findings challenge the conventional notion of a sharp COB and support a more transitional, structurally complex Continent-Ocean Transition Zone (COTZ). The study highlights the need for revised mapping protocols and further investigation into the thermal and temporal evolution of these magmatic features to better understand the onset of oceanic spreading.