The Northern and Southern Scandes — structural differences revealed by an analysis of gravity anomalies, the geoid and regional isostasy

Abstract

We investigate the Scandes mountain range by analysing the gravity field, the geoid heights and the degree of isostatic compensation of the lithosphere. Topographically, the Scandes mountain range can be divided in the Northern and Southern Scandes. 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. Geoid heights reduced by the effect of topographic masses show a large-scale minimum in the Northern Scandes, but no anomaly in the Southern Scandes. Regional, flexural isostatic calculations yield a flexural rigidity of D = 10 23 Nm for the lithosphere of the Southern Scandes and the isostatic gravity and geoid residuals point to additional isostatic support by low-density rocks below the Moho. On the other side, for the lithosphere in the Northern Scandes no significant flexural rigidity can be resolved. Here, the Bouguer anomaly is best modelled with a small flexural rigidity, indicating nearly Airy isostatic behaviour. Local subsurface loading and horizontal tectonic forces overprint the isostatic compensations and increase the tectonic complexity of the Northern Scandes. These distinctive features of the Scandes cannot be explained by currently existing models of the present and Neogene uplift and the isostatic mechanism of the Scandes.