BASEMENT STRUCTURE OF THE CONTINENTAL-MARGIN IN THE LOFOTEN-LOPPHAVETAREA, NORTHERN NORWAY - CONSTRAINTS FROM POTENTIAL-FIELD DATA, ON-LAND STRUCTURAL MAPPING AND PALEOMAGNETIC DATA

Magnetic and gravity anomalies within the northern Norwegian margin, 6 7 degrees to 71 degrees N are generally interpreted in terms of a comp lex series of uplifted and rotated basement blocks. Some of the baseme nt highs were previously not identified on seismic reflection data bec ause they lie below basalt Bows. Several shifts in polarity occur alon g the faults in the continental shelf and the adjacent onshore area. T his is most pronounced along the Ribban and Vestfjorden Basins and fur ther to the northeast along the Vestfjorden-Vanna fault complex. The i ndividual segments of the fault complexes are connected by transfer zo nes, which occur as either: (1) transverse faults, e.g. the Lenvik tra nsfer zone, or (2) twist zones, e.g. the Vesteralen transfer zone. The Vestfjorden Basin consists of two subbasins or half-grabens: one to t he north with a border fault to the east and one to the south with a b order fault to the west. Several basement faults on the continental sh elf can be traced onto the mainland. Reactivation of old shea zones is commonly observed. The Senja Fracture Zone is a reactivation of the P roterozoic Bothnian-Senja fault complex. A palaeomagnetic study of Ves teralen, Senja and Kvaloya has furnished temporal constraints on the n ear-shore fault activity. On Senja and Kvaloya, two phases of faulting and brecciation have been identified. A young phase, associated with the formation of fault-gouges, is recent-Tertiary in age, whereas an o lder phase, associated with brecciation, is of Permian age. The lack o f Cretaceous/Jurassic faulting along the central Vestfjorden-Vanna fau lt complex indicates that there may have been a westward shift of the regional fault activity in the Nordland-Troms area from the Carbonifer ous-Permian to the late Jurassic-early Cretaceous.