Summary
An interpretation of aeromagnetic, gravimetric and petrophysical data from the Norwegian Sea between 67°N and 71°N is reported. Most of the magnetic and gravity anomalies within the survey area may be interpreted in terms of a fault-related basement relief. Depth to basement estimates based on gravity and aeromagnetic data are 5 km and 10 km, respectively, in the Ribban Basin. The discrepancy between the two estimates is most likely caused by downfaulted Caledonian Nappes, Devonian sediments or amphibolite-facies gneisses. The gravity modelling indicates that the Lofoten - Vesterålen area constitutes a basement high within the rifted and thinned crust of the continental shelf, similar to the basement highs within the Vøring Basin to the South. The depth to the basement is calculated to c. 10 km in northern part of the Træna Basin and c. 9 km in the Røst Basin. A correlation between Jurassic-Cretaceous faulting and underlying basement topography indicates that the deep structural setting may have guided the location of the later faulting. Within the Utrøst Ridge - Ribban Basin the basement map shows a complex pattern with several up- lifted and rotated basement blocks. The Vestfjorden Basin seems to consist of two sub-basins or half grabens; one to the north with a boundary fault to the east and one to the south with a boundary fault to the west. To the west of the Bodø High, and northwards along the shelf edge, there is a continuous zone of high frequency anomalies interpreted as the eastward termination of intrasedi- mentary volcanic rocks. The aeromagnetic and gravity data indicate that the Precambrian rocks in the Lofoten-Vesterålen area, despite Mesozoic reactivation along possible Caledonian zones of weakness, are situated within the margin of the Baltic Shield. They probably constitute a deep section of the Transscandi- navian Granite-Porphyry Belt.
