New OBS Data Constrain the Crustal Structure of the Lofoten-Vesteralen Margin off Norway

A new ocean bottom seismometer/hydrophone (OBS/OBH) survey, as part of the Euromargins 2003 OBS Experiment, was performed along the ~400-km-long Lofoten-Vesterålen margin off Norway. Analysis of the new data and compilation of earlier wide-angle seismic velocity profiles, integrated with an extensive seismic reflection data set and crustal-scale two-dimensional gravity modelling, constrain the margin crustal structure. The analysis shows that there is a distinct continent-ocean transition (COT) zone defined by rapid crustal thinning between the continental crust near the shelf edge and the oceanic Lofoten Basin. The COT, which decreases in width northward along the Lofoten-Vesterålen margin, is underlain by a rapidly increasing depth to Moho from typical oceanic crust near magnetic anomaly 23 to a 20-26-km continental crustal level at the shelf edge. Furthermore, there is convincing evidence for sedimentary sequences below the breakup lavas east of the continent-ocean boundary, which is identified close to the foot of the continental slope by a persisting magnetic and seismic signature along the margin. Close to the continental slope, a steep and relatively narrow, 10-40-km-wide, Moho-gradient zone exists within the COT. To the south, the Moho-gradient zone continues along the Vøring margin, however it becomes offset 70-80 km to the northwest along the Bivrost Fracture Zone/Lineament. We interpret the crustal structure and properties of the Lofoten-Vesterålen margin, and its contrast with adjacent margin provinces, to be governed by the oblique position of the Early Tertiary line of opening relative to the Late Jurassic-Early Cretaceous central rift zone. In a regional sense, the Lofoten-Vesterålen margin is located on the east flank of the Late Jurassic-Early Cretaceous rift, which may explain the relatively small Cretaceous subsidence. The margin may also be considered the elevated footwall of a hanging wall basin below the lavas west of the shelf edge continuing onto the conjugate NE Greenland margin. Within this framework, the southern boundary of the Lofoten-Vesterålen margin, the Bivrost Fracture Zone and its landward prolongation, appears as a major across-margin magmatic and structural crustal feature governing the margin evolution.