Deep crustal structure of the northern North Sea Viking Graben: results from deep reflection seismic and gravity data

Abstract

The combination of deep reflection seismic interpretation (NSDP 84 data set) and 3-D modelling of free-air gravity data resulted in a regional crustal model for the Viking Graben area. The interpretation focuses on the structure of the crystalline crust which is displayed by depth sections, a map of the Moho, a map of the thickness of the crystalline crust and a map of the extension factor β. The thickness of the crystalline crust varies from 10 km near the centre of the graben to 30 km under the adjacent platforms. The thickness of the sedimentary cover varies from 11 km to 1 km, respectively. The topography of the Moho reflects, in a highly smoothed way, the top of the crystalline basement. The “seismic” Moho coincides with the “gravity” Moho, although some discrepancies are observed in the most extensively stretched areas. High β-values are observed, but no indications of the presence of oceanic-type crust associated with a crustal rupture have been found. The results are thought to favour a stretching model of graben development. A strong inclined reflection and associated reflection patterns in the East Shetland Platform are tentatively interpreted as a fragment of the Iapetus Suture. The asymmetrical structure of the graben is assumed to be associated with initial inhomogeneities in the crust.