GEOMORPHOLOGY AND TOPOGRAPHY OF RELICT SURFACES: THE INFLUENCE OF INHERITED CRUSTAL STRUCTURE IN THE NORTHERN SCANDINAVIAN MOUNTAINS

Although the Scandinavian mountains were deeply incised during Pleistocene ice ages, the presence of smooth, subhorizontal erosional surfaces at the tops of many ridges and peaks has long been postulated as evidence for Cenozoic uplift of old erosional surfaces. The age and origin of these surfaces is controversial. Because some surfaces coincide with deeply weathered zones, many workers have concluded that they are pre-Pleistocene, perhaps Mesozoic in age, and that their morphology has been largely preserved beneath cold-based glaciers and ice sheets. Here we analyze the distribution of the relict surfaces with respect to the margin-scale crustal architecture, defined by the continent-ocean boundary (COB), the taper break (TB; the point where crustal thickness decreases to <10 km) and the onset of "unstretched" crust (defined as 37-41 km thick). This architecture developed during latest Jr-Early K time.

Elevation contours on the surfaces, a smoothed fit to mean elevations, and histograms of elevation distribution show three distinct, coast-parallel belts onshore mainland Norway, and a somewhat different pattern in the coastal Lofoten-Vesteralen archipelago. The sharp transition from higher, continuous surfaces to lower, stepped, and discontinuous surfaces occurs at the boundary between the central and eastern belts and is located where the crust begins to thin rapidly to the northwest, coincident with the 38 km crustal thickness contour.

From the coast to the crest of the range, regions of low relief tend to exhibit low-elevation surfaces while regions of high relief exhibit high-elevation surfaces. From the crest inboard, relief decreases dramatically but surface elevations remain relatively high. Furthermore, the 38 km thickness contour typically coincides with a step in both relief and elevation perpendicular to the margin. In margin-parallel transects, elevations in the eastern belt remain high for >100 km north of the Senja Fracture zone (transform) and then decrease systematically further northeast.

The along- and across-strike pattern and the correlation with extension-related structures such as the TB suggest Scandinavia's present-day topographic envelope reflects a crustal strength profile set up during an earlier stage of extension rather than that imposed due to opening of the Atlantic.