Magmatic development of the outer Voring margin from seismic data

The Voring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired over the margin. One profile crosses from the VOring Plateau to the VOring Spur, a bathymetric high north of the EJMFZ. The P wave data were ray traced into a 2-D crustal velocity model. The velocity structure of the VOring Spur indicates up to 15 km igneous crustal thickness. Magmatic processes can be estimated by comparing seismic velocity (V-P) with igneous thickness (H). This and two other profiles show a positive H-V-P correlation at the VOring Plateau, consistent with elevated mantle temperature at breakup. However, during the first 2 Ma magma production was augmented by a secondary process, possibly small-scale convection. From approximate to 51.5 Ma excess melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the VOring Spur shows that it was created by at least two uplift events, with the main episode close to the Miocene/Pliocene boundary. Low H-V-P correlation of the spur is consistent with renewed igneous growth by constant, moderate-degree mantle melting, not related to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, precluding that compressional flexure at the EJMFZ uplifted the high. We find a proposed Eocene triple junction model for the margin to be inconsistent with observations.