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The Scandes mountain range is located at the western edge of the Fennoscandian shield and includes two dome-like areas of high mountains and plateaus, the Northern and Southern Scandes. In the present, Fennoscandia and adjacent areas are largely affected by high uplift rates, but prior to the post-glacial rebound the Scandes may have been partly uplifted during Plio-Pleistocene time, as part of a circum Atlantic belt of Neogene uplifts, for which the mechanism is still under discussion.
The gravity field and the geoid heights provide means to study the structural differences within the Scandes and the mechanism of exhumation of the mountain range. Comparisons between the present topographic expression and the gravity field and the geoid show that the axis of highest elevation in the Northern Scandes is shifted eastwards compared to the minimum of the Bouguer anomaly, while the two coincide perfectly in the Southern Scandes. Seismological studies have not imaged a pronounced crustal root along the entire mountain range, which is however pointing against simple local isostatic compensation. The question arises about the source for the Bouguer gravity low, if it is not correlating with a crustal root. Here, a 3D lithospheric density model is presented, which explains the gravity signal and isostatic balance by taking into account a high-density lower crust below the Fennoscandian shield and considering an upper crustal structure, the Transscandinavan Igneous Belt. The main element to explain the gravity low along the Scandes is the lower crust, which has increased densities relative to the upper crust and reaches a maximum thickness of up to 25 km below the Fennoscandian shield, while it is tapering out below the Scandes. Imaging the top of this lower crustal body mimics the missing root of the Scandes. Hence, the isostatic balance along the Scandes mountain belt is achieved by lateral density variations in the crust and upper mantle.
These distinctive features of the Scandes cannot be convincingly explained by currently existing models of the present and Neogene uplift and the isostatic mechanism of the Scandes. A common mechanism for the uplift of southern and northern Norway has yet to be found and may be superposed by secondary effects as dynamic topography due to the opening of the North Atlantic. Furthermore, the present shape of the Scandes mountain chain is intimately linked with the structure of the offshore margin system. Onshore Norway, major detachments stemming from the Late Caledonian orogenic collapse of the Scandes control the crustal geometry and can be traced into the deep Møre and Vøring basin, offshore Norway and are a key candidate for the distribution of large-scale tectonic stresses in the mountain belt.
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