Burial of the Mohn‐Knipovich seafloor spreading ridge by the Bear Island Fan: Time constraints on tectonic evolution from seismic stratigraphy

Six seismic multichannel profiles and multibeam bathymetric data were collected during 2000 and 2001 from the Mohn‐Knipovich spreading ridge bend in the Norwegian‐Greenland seas. The full spreading rate is slow to ultraslow (15–17 mm a −1 ), characterized by both magmatic and amagmatic spreading and lack of transform faults. The area is covered by sediments from the Bear Island Fan, and the proximity of the ridge to a glacial margin with high sedimentation rates provides a unique opportunity to study the timing and tectonic development from seismic data. The sediments in the current study have been dated by correlation to the Bear Island Fan seismic stratigraphic network. The magma‐starved northern part of the study area has an asymmetric axial valley which is deepest to the west, whereas the axial volcanic ridge in the southern part is more symmetric. The western axial mountains are about 600–800 m higher than the eastern, and the sedimentary architecture shows that almost all tectonic activity after 1.3 Ma occurred on the western side. Low‐angle (20°–50°, typically 25°) faults are ubiquitous, even at initiation. Little interaction between sedimentation and block rotation indicates rapid, short‐lived episodes of fault movement at the axial flank. Detachment and starting core complex development on the western side can explain the asymmetric tectonic development of the axial mountains, difference in elevation, recent quiescence of the eastern axial mountains, and the existence of older corrugated surfaces in the west.