A study of basement structures and onshore-offshore correlations in Central Norway

Abstract

A combined interpretation of gravity, aeromagnetic and petrophysical data is reported. The estimated depths to the top of the crys talline basement in the More Bas in show that the sedimentary deposits are thicker than 14 km. In the More Basin, the basement features reveal a deeply buried, rift­ related relief at pre-Cretaceous, or possibly Jurassic, leve!. On the Trondelag Platform, a series of structural highs and lows with NE-SW and NNE­ SSW strike, modified by N-S relief, occur. From the aeromagnetic map, the oldest (Devonian) extensional structures have been interpreted to extend from the land on to the shelf. The detachments exhibit a NNW-SSE trend in the shelf, which is locally modified by ENE-WSW-to NE-SW-trending synforms and antiforms, and by the post-Devonian faulting. Regional gravity modelling has been performed along the only modem seismic reflec­ tion line that crosses the Scandinavian mountains. The combined analysis of the deep seismic data and gravity modelling, constrained by density data, indicates that the negative Bouguer anomalies approximately ali gned al ang the axis of the Scandinavian mountains are the combined effect of: l) Mo ho topography and 2) Lateral density variations between the Western Gneiss Region, the Transcandinavian Igneous Belt and rocks of the Sve­ cofennian domain. This suggests a combined Airy- and Pratt type of isostatic compensation/mas s balancing of the central Scandinavian mountains. Several high-amplitude magnetic anomalies on land and in the adjacent eastern continental shelf are interpreted to represent high-grade rocks. These occur along same of the major fault wnes and known rift flanks, possibly in association with basement antiforms.