Transition from amagmatic to volcanic margin: Mantle exhumation in the Vøring Basin before the Icelandic plume influence

Abstract

The outer Vøring Basin, Norwegian Sea, is an abnormally deep and distal part of the Norwegian passive margin, known as “magma-rich”. Yet, the lastest borehole drilled in its northernmost part led to a drastic change in the interpretation of seismic reflection data. This update motivates a new model for the entire Mesozoic-Eocene rifting period. Here I evaluate the link between tectonics, serpentinization and magmatism in the Norwegian margin from the Ryazanian-Valanginian to the Palaeocene-Eocene magmatic breakup. Maps of the regional Nise sandstones and main regional unconformities specifically highlight the fundamental role of the Nyk-Vema Structure to understand the basin and to question the deformation timing related to deep structures. The top of partially serpentinized mantle is supported by high-amplitude reflectors clearly visible on certain seismic lines, known as “T-Reflector”, covered with gravity-driven pre-exhumation sediments and further deposits. A new structural scheme based on the interpretation of 2D and 3D seismic data shows the complex organization of fault networks and constrains a major deformation period between the Late Campanian and the Late Palaeocene. Ocean-scale complementary arguments are in good agreement with Lower-Cretaceous mantle exhumation. Before becoming a volcanic margin in the Palaeocene, this segment of the Norwegian margin appears as amagmatic until the Late Campanian, at least. I propose an integrated model since the onset of hyperextension in the end of the Jurassic until the cessation of activity of the Aegir Ridge in the Miocene. This model has implications regarding the context-dependent interpretation of lower-crustal bodies, the ubiquity of serpentinization and mantle exhumation worldwide, and on the hydrocarbon system.