The regional resultant stress field of the northeastern North Atlantic has shifted significantly throughout the Phanerozoic. In Fennoscandian parts of the Caledonian orogen, mountain building, which was characterized by NW-SE contraction (reference to present North), was followed by a collapse with transport both parallel and transverse to the mountain chain. The Late Palaeozoic – Mesozoic saw several stages of E-W to NW-SE extension, varying in time and position. Local episodes of inversion are traceable in some cases, particularly in connection with deep-seated and long-lived zones of weakness. The Cenozoic has to a larger degree been affected by compression, including folding and basin inversion. Again some of the more pronounced effects of local inversion are related to pre-existing fault systems. Neogene uplift of the western mountainous area in Scandinavia can be unravelled by potential field study, AFT data and reflection seismic sections. Assuming that the region is close to isostatic equilibrium, the uplifted areas must be supported at depth by substantial volumes of low-density material within the crust or the mantle, close to the crust/mantle interface or close to the lithosphere/asthenosphere interfaces.
A series of NW-SE-oriented cross-sections, representing successive stages of development from the late Caledonian to Present were prepared and used to analyse the tectonomorphological development as related to the shifting stress configurations. Three stages are inferred:
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Stage 1; Devonian – late Permian denudation of the Caledonian mountain chain: During the latest stage of closing of the Iapetus Ocean in early to mid Devonian times, the Caledonian mountain chain reached its maximum elevation of perhaps as much as 8–9 km. Including the foreland basins to the east, the average topographic gradient of the eastern flank may have been in the order of 1,3°. The denudation of the Caledonian mountains continued into the Permian and by the end of the Permian, the mountain system was more or less obliterated with a gradient of the eastern flank probably continued to fall to less than 0,1°.
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Stage 2; Triassic – late Cretaceous; Tectono-thermal uplift of central south Norway. Uplift of central south Norway was rejuvenated in Triassic times and continued throughout the Jurassic and early Cretaceous. The gradient of the eastern flank increased to a maximum of approximately 0,15° and master structural elements like the Lærdal-Gjende-Olestøl Fault Complex again played important roles in the development.
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Stage 3; Tertiary – Present; Renewed tectono-thermal activity and post-glacial rebound. A second phase of post-Caledonian tectono-thermal uplift of south central Norway started in Oligocene time, again increasing the gradient of the eastern flank of south Norway (around 0,2°).