Josep Maria Verges

Deep structure of the Vøring Margin: the transition from a continental shield to a young oceanic lithosphere

The present-day lithospheric structure across the Norwegian Margin in the Voring region is presented. The Voring Margin is characterized by the presence of large volume of magmatic underplating, thick Mesozoic basins, and prominent crustal thinning. Results from recent deep seismic experiments in the Voring Basin and Voring Marginal High and 3-D gravity modelling have been implemented in a regional 2-D lithospheric transect that runs from the Norwegian Caledonian Belt to the oceanic domain, crossing the transition between the Precambrian Fennoscandian/Baltic shield and the Cenozoic northern North Atlantic oceanic lithosphere. The modelling approach integrates elevation, gravity, geoid and heat flow data under the assumptions of thermal steady-state and local isostasy. The results confirm and refine the major trends of the crustal geometry which is characterized by a Moho depth varying from about 45 km beneath the Caledonian thrusts, to 30 km beneath the Trondelag Platform, to 20–14 km beneath the Voring Basin and to 13 km in the oceanic domain. The lithosphere thins from the Norwegian Caledonian Belt (190 km thick) to the oceanic domain (<60 km) in a stepwise manner reflecting the progressive seawards migration of lithospheric deformation since the Paleozoic. Our lithospheric thickness results are different from those predicted by post-rift lithospheric cooling models. In the oceanic domain, observed residual bathymetry (∼600 m) is interpreted as the remaining effect of a deep seated thermal perturbation during the upper Cretaceous which would also produce a heat flow anomaly of ∼15 mW m−2. Alternatively, residual bathymetry can be interpreted in the absence of thermal anomalies as produced by depletion of the sublithospheric mantle extending down to 130–230 km depth depending on the density contrast (10–30 kg m−3).

Lithospheric structure of the Mid-Norwegian Margin: comparison between the Møre and Vøring margins

The lithospheric structure across the Møre Margin has been studied by integrating regional elevation, gravity, geoid and heat-flow data together with available seismic and geological data. Our results show that the Moho depth varies from 42 km beneath the Caledonides to 20–15 km beneath the basin and to 13–16 km in the oceanic domain. The lithosphere thins in a step-like manner from 160 km inland to 60–80 km in the oceanic domain. A comparison with the Vøring Margin reveals that both margins have similar crustal and lithospheric structures. Major dissimilarities are: (1) the volume of underplating beneath the ocean–continent boundary; (2) the lithospheric thickness beneath the Caledonian Front; (3) the lithospheric thickness beneath the distal parts of the margins. The heat transfer across the Vøring Transform Margin, the secular variation of lithospheric thickness with age, and the jump of the Aegir spreading ridge are responsible for these differences.