The Aegir Ridge: Structure of an extinct spreading axis

Abstract

In 1988 a reflection seismic survey was carried out by the Alfred‐Wegener‐Institute for Polar and Marine Research to study structure and development of the Aegir Ridge, an extinct spreading axis in the Norway Basin. A number of volcanolike structures were detected in the central ridge. The emerging lava flows dip away from their source in ridge strike. Perpendicular to ridge strike, we observed lava flows dipping towards the ridge center. This pattern might represent a more general flow pattern at mid‐ocean ridges. After spreading ceased, sedimentation resulted in the deposition of 800 ms two‐way time (TWT) to 1300 ms TWT (about 900–1400 m) sediments in the central ridge. Distribution of the sediments indicate subsidence of the central ridge probably due to cooling after termination of spreading. This subsidence started no later than late Oligocene or early Miocene. We detected an area where migration of a fluid phase led to obstruction of the sedimentary layering and the formation of mounds and faults at the ocean bottom. Several sources for the fluid phase are discussed.