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Marco Broenner, Geological Survey of Norway (Norway)
Odleiv Olesen, Geological Survey of Norway (Norway)
Janusz Koziel, Geological Survey of Norway (Norway)
Tormod Henningsen, StatoilHydro ASA (Norway)
Peter Midboe, StatoilHydro ASA (Norway)
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The Lofoten and Vesterlen region represents the narrowest part of the Norwegian shelf and is situated in the transition zone between the Mid-Norwegian passive continental margin and the sheared southwestern Barents sea. The region must be considered as a key area in the face of the varying tectonical conditions and the structural development of the continental margin. It is characterized by a complex system of uplifted and rotated basins, flanked by a network of steep deep faults. Offshore between the islands and the mainland deep Mesozoic basins still exists but the structural settings are barely known. Andøya is the northernmost island of this region and is the only place in Norway to study exposed Mesozoic rocks on land. The combined observation and interpretation of Mesozoic faulting and onshore basement structures allows a more accurate and differentiated interpretation of the continental margin.
With the aim to map structural elements of the island and to get a better understanding of the complex basement geometry of Andøya and the Andfjorden area a high sensitivity aeromagnetic survey with dense line spacing of 200m was carried out in 2007 in the Rams area of Andøya, Vesterlen. The survey area is situated at the northeastern part of the island and covers an onshoreoffshore area of c. 158 km2. The line direction was NNE-SSW and a total of c. 11000 km was flown. The magnetic sensor altitude was approx. 70 m. Data processing comprised spike removal and data editing, IGRF correction, diurnal variation correction, and micro-levelling. Various filters were applied and analytic signals were calculated to map structural elements, which were used for a combined interpretation with petrophysical, seismic and gravity data. 3D Euler deconvolution was applied to estimate the depth to the magnetic sources.
Due to different orientation of magnetic elements a separation of the study area into at least five provinces was carried out. Within theses provinces the predominant striking changes clockwise from WNW-ESE in the south over NW-SE to NNW-SSE in the north. From high-resolution magnetic data additional structures were mapped, complementing the structural and geological image. Offshore Andøya between Skarstein and Breidvika a wedge-shaped basement deepening appears, running in an almost N-S direction parallel to the shoreline. The deepening marks the western rim of the Mesozoic basin in the Andfjorden. The combined interpretation with gravity and available seismic profiles reveals a further segmentation within the basin and provides additional information of the tectonic development of the area.
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