HR: 09:15h
AN: GP31A-06 INVITED    [Abstracts]
TI: New insights into the structure of Norwegian continental margins from modern aeromagnetic compilations
AU: * Ebbing, J
EM: Joerg.Ebbing@ngu.no
AF: Geological Survey of Norway, Leiv Eirikssonsvei 39, 7491, Trondheim, Norway
AU: Olesen, O
EM: Odleiv.Olesen@ngu.no
AF: Geological Survey of Norway, Leiv Eirikssonsvei 39, 7491, Trondheim, Norway
AU: Gernigon, L
EM: Laurent.Gernigon@ngu.no
AF: Geological Survey of Norway, Leiv Eirikssonsvei 39, 7491, Trondheim, Norway
AU: Skilbrei, J R
EM: Jan.Skilbrei@ngu.no
AF: Geological Survey of Norway, Leiv Eirikssonsvei 39, 7491, Trondheim, Norway
AB: We present the aeromagnetic compilation of the Norwegian mainland and its shelf area and its importance for geological models and tectonic studies. The combined data-set reveal that the bedrock structures are continuous from the Baltic Shield under the Caledonian orogen into the continental shelf and that the late-Caledonian collapse of the Caledonian orogene has influenced the style of extension on the Norwegian shelf. On the margin, modern high-resolution aeromagnetic surveys with small line-spacing, more accurate navigation and sensitive magnetometers have revealed the existence of significant magnetic anomalies arising from sedimentary layers. Sub-cropping Late Paleozoic to Tertiary sedimentary units along the Trøndelag-Nordland coast produce a very distinct anomaly pattern. The asymmetry of the anomalies, with a steep gradient and a negative anomaly to the east and a more gentle gradient to the west, relate the anomalies to a strata gently dipping westward. Susceptibility measurements on core samples, hand specimens and in situ on bedrock exposures are essential for the interpretation of these anomalies. Remapping of the oceanic crust has also improved our under-standing of the Tertiary opening of the North Atlantic as previously interpreted oceanic fracture zones zones do not exist; these were artefacts of poor navigation and wide line spacing of the vintage datasets. Tectonic reconstruction has shown that the opening of the Norwegian-Greenland Sea between the Jan Mayen and Senja fracture zones occurred along a stable axis without offsets of the oceanic spreading anomalies and without jumps in spreading axis. Transfer zones have previously been associated with oceanic fracture zones along the Mid-Norwegian and East-Greenland margins. Transfer zones are important entry points for sedimentary drainage systems, a relationship that has also been suggested for the transport of Cretaceous sands to the mid-Norwegian margin. Our new interpretation has consequently implications for evaluating the petroleum potential in the Vøring Basin, Mid-Norway. A high-resolution survey of the Oslo Graben changed our understanding of this Permian Rift. The magnetic field data of the Oslo Graben area are unique since two surveys recorded at different flight altitudes (50 m above ground and 3400 m above sea level) exist. The magnetic anomaly reaches values up to 1500 nT over an elongated area of 75 by 30 km. Local structures, such as calderas, ring fracture zones and their associated circular-shaped magnetic anomalies are a first order feature in the aeromagnetic data. Analysis of the depth-to- bottom of the magnetic sources and forward modeling indicates the presence of a more than 15 km thick intrusion beneath the Oslo Graben. The intrusion is interpreted to indicate a differentiation series from base (gabbro) to top (granite). This petrological variation with depth is not detectable in the gravity anomaly because of the small density contrast to the surrounding crust.
UR: http://www.ngu.no
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 1540 Rock and mineral magnetism
DE: 8015 Local crustal structure
DE: 8104 Continental margins: convergent
DE: 8169 Sedimentary basin processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting