Why are there mountains in Norway? And why are there mountains along many other passive continental margins around the world; e.g. along the Atlantic margin of Brazil, in East and West Greenland and in southern India? These questions have been debated intensely over the last decades, but answers cannot be given without knowing the time at which the elevated topography formed. In the Norwegian case, the rocks that form the mountains are more than 400 Myr old and thus do not provide any direct evidence of the geological development over that time span.
This huge gap in the geological record of the Norwegian mountains – and similar time gaps for other elevated passive continental margins (EPCMs) around the world – has led to a variety of estimates of the age of the mountains that reveal geoscientific disagreements of a spectacular magnitude (Japsen et al. 2012, 2018; Green et al. 2013, 2018). Are the elevated margins remnants of ancient orogens? Were they formed as rift shoulders during rifting or break-up? Or are they the result of Neogene epeirogenic uplift? These estimates for the age of the Norwegian mountains range from about 400 Ma to 20 Ma; a factor of 20 in age estimates that illustrates fundamental disagreements; not only about first-order geological observations of passive margins on all continents but also about the geodynamic processes that shape the surface of the Earth.
Once the timing for the formation elevated topography of a margin has been established, it may be possible to speculate about the mechanism(s) that drive the vertical movements. How far are we from identifying geodynamic models that are capable of providing predictions that can be tested and calibrated by data from the world’s passive continental margins?
Green, P.F., Lidmar-Bergström, K., Japsen, P., Bonow, J.M. & Chalmers, J.A. 2013: Stratigraphic landscape analysis, thermochronology and the episodic development of elevated passive continental margins. Geological Survey of Denmark and Greenland Bulletin 2013/30, 150 pp. (free download from www.geus.dk).
Green, P.F., Japsen, P., Chalmers, J.A., Bonow, J.M. & Duddy, I.R. 2018: Post-breakup burial and exhumation of passive continental margins: Seven propositions to inform geodynamic models. Gondwana Research 53, 58–81.
Japsen, P., Chalmers, J.A., Green, P.F. & Bonow, J.M. 2012: Elevated, passive continental margins: Not rift shoulders, but expressions of episodic, post-rift burial and exhumation. Global and Planetary Change 90-91, 73-86.
Japsen, P., Green, P.F., Chalmers, J.A. & Bonow, J.M. 2018: Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces. Journal of the Geological Society, London 157, 721-741.