NJG71-4-02
1991
Separate gravimetric and magnetic anomaly sources: deep Permian intrusions at Nes, Hedmark
71
4
pp. 249-258

A broad elongated aeromagnetic anomaly striking N40E occurs in the central part of the Mjøsa district at Nes and Brumunddal, southern Norway. Previous magnetic investigations from the area have indicated a source depth of about 1700 m. The source was assumed to be a Permian pluton consisting of larvikite, because of the rhomb-porphyry situated north of Brumunddal. Magnetic modelling, using a typical susceptibility of larvikite, gives a depth of about 2500 m. A small local anomaly that strikes across the main anomaly in the western part of the Precambrian gneiss complex of the horst at Liberget-Solbergåsen is found to be associated with vertical magnetic layers in the Solbergåsen rock complex. The magnetic layers are assumed to be granodiorite. A residual gravity anomaly map constructed based on old and new gravity data shows a negative anomaly associated with the eastern part of the horst, Liberget, which contains granite. It is probable that the horst continues across Furnesfjorden and further east. The main aeromagnetic anomaly has a strike that differs from that of the gravimetric residual anomaly, indicating separate magnetic and gravimetric sources. The western part of the horst, Solbergåsen, is associated with a small positive gravimetric anomaly. The Furuberg Formation situated south of Solbergåsen has a low density and is associated with a small negative anomaly. The gravity modelling gives fairly shallow sources.

K. Røthing, Norwegian Mapping Authority, Geodesy Division, Monserudveien, N-3500 Hønefoss, Norway; E. Gjøen, University of Bergen, Institute of Solid Earth Physics - Geomagnetism, A/legt 70, N-5007 Bergen, Norway.

 

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