Rates of continental breakup magmatism and seafloor spreading in the Norway Basin-Iceland plume interaction

[ 1] In year 2000, an ocean bottom seismometer (OBS) profile was acquired across the More margin to the Aegir Ridge, an extinct seafloor spreading axis. The margin is an early Eocene volcanic passive margin, located between the Faeroe-Iceland Ridge ( FIR) and the East Jan Mayen Fracture Zone (EJMFZ). The P wave data were modeled by ray tracing to give a crustal transect showing a 10 - 11 km thick igneous crust created by breakup magmatism, tapering off to magma-starved seafloor spreading by C23 time (51.4 Ma). The location of the EJMFZ was reinterpreted from a satellite derived gravity map, and spreading direction in the Norway Basin reevaluated. No other fracture zones were confirmed, and both thin oceanic crust ( 4 - 5 km) and lack of fracture zones resemble ultraslow spreading on the Arctic Gakkel Ridge. Magnetic seafloor spreading anomalies were identified from the magnetic track recorded with the OBS profile, and half spreading rates were derived. Early seafloor spreading was slow ( 15 - 32 mm yr(-1)), approaching ultraslow ( 6 - 8 mm yr(-1)) by C20 time (42.7 Ma). AV- shaped pattern seen in the gravity field located only around the northern part of the Aegir Ridge corresponds to increased crustal thickness in the seismic model, recording northeast transport ( 3 - 6 mm yr(-1)) of more melt-fertile asthenosphere zones. The magma-starved character of the Norwegian Basin seen also during slow seafloor spreading may be the result of depletion of the asthenosphere when the Iceland plume constructed the FIR to the south, as the asthenosphere is subsequently transported into the Norway Basin.