Crustal structure of the southern part of the Vøring Basin, mid-Norway margin, from wide-angle seismic and gravity data

Abstract

During the summer of 1996, five profiles with a total length of 892.5 km and 30 recovered Ocean Bottom Seismographs (OBSs) were acquired along the southern part of the Vøring Margin, mid-Norway. These profiles are oriented in both strike and dip direction, mapping the crustal structure along the western-most part of this area. By performing both forward and inverse velocity travel-time modelling of the vertical components of the OBSs (P-waves) regional models have been established. The thickness of the Cenozoic sediments ranges from 0.5 km at the structural highs (Møre Marginal High) to more than 3 km in the Vigrid Syncline. The Cretaceous layers vary considerably in thickness, from 1.7 km close to the Jan Mayen Fracture Zone, increasing to approximately 8 km below the Helland Hansen Arch. Several intrusions are found in the Cretaceous layers and they individually range in thickness from 0.1 to 0.6 km. These intrusions can be followed through crossing profiles, in both in the models presented in this paper, and in the models inferred from earlier OBS surveys along this margin. The pre-Cretaceous sediments are modelled as a layer with P-wave velocity of more than 5 km/s. The thickness of this layer is generally less than 5 km, but locally a thickness of 6.5 km is modelled. The crystalline basement is modelled as a 6+ km/s refractor with a general trend shallowing towards south- and northwest. Along a strike-profile, the transition from continental to oceanic crust is modelled by increased P-wave velocity from 6.2 to 7.3 km/s, as the profile crosses the Jan Mayen Lineament towards the Møre Marginal High. The thickness of the continental crystalline basement is largest landward towards the Helland Hansen Arch where it exceeds 10 km. Towards the SW and NW, where the crystalline basement is elevated, the thickness decreases to less than 5 km. In the lower crust, a high velocity 7+ km/s body, interpreted as magmatic underplating, is found along three of the profiles in the present work. The SE boundary of this magmatic underplated layer is located beneath the Helland Hansen Arch and towards the Møre Marginal High. The southwestward termination is less certain, but the Jan Mayen Fracture Zone seems to control the emplacement of intrusions in the southern Vøring Basin. The depth to Moho varies from 12 to 28 km, deepening landwards.