STRUCTURE OF A VOLCANIC CONTINENTAL-MARGIN DERIVED FROM OCEAN-BOTTOM SEISMOGRAPHIC DATA - THE NORTHERN VORING MARGIN, OFF NORWAY

This paper presents a crustal model derived from an Ocean Bottom Seism ograph (OBS) study along the northern Voring margin off Norway. The pr ofile was acquired to map the crustal structure in the northernmost pa rt of the Voring Basin, and to link crustal models of the Lofoten and central Voring Basin obtained by previous OBS studies. The Voring marg in, as well as the Lofoten margin to the north, was created by contine ntal breakup between Norway and Greenland in late Paleocene-early Eoce ne. The rifting and continental breakup process were accompanied by in tense extrusive and intrusive magmatic activities. The OBS data provid e the whole crustal structure along the northern Voring margin? in the area where the deep crustal structure cannot be resolved by conventio nal multichannel reflection data due to sill intrusions in the sedimen tary sequence. The shallow part of the crustal model is characterized by up to 10 km thick sediments, a sequence of flood basalts and sill i ntrusions. The P-wave velocities in the flood basalts and sill intrusi ons are estimated to 5.0 km/s and 4.7-5.8 kms, respectively. The model indicates an abrupt thickening of the upper crystalline crust from si milar to 3 km in the NE, to about 10 km towards the SE, with velocitie s of 6.0-6.2 km/s. The lower crustal velocities are not well resolved due to lack of clear refraction arrivals from the lower crust. However , the observed amplitude versus offsets are best explained by a model with a change in lower crustal velocities from 6.8 to 7.2 km/s beneath the Bivrost lineament. The modelling infers the presence of a lower c rustal reflector beneath the lineament, which represents the landward continuation of the Bivrost lineament. Reflection arrivals from the Mo ho reveal a Moho depth of 23 km in the middle of the profile and 18-20 km in the northeastern part of the profile. 4 370 km long crusta: sec tion from the central part of the Voring Basin to the Lofoten margin, obtained by the results of this study and previous OBS studies, shows a simple thinned continental crust on the Lofoten margin, and a high v elocity lower crust underlying an upper crust of varying thickness in the Voring Basin. The transition between these structures is situated beneath the Bivrost lineament in the lower crust, and beneath the base ment high about 40 km south of the lineament in the upper crust.