Deformation partitioning in a slow spreading ridge undergoing oblique extension: Mohns Ridge, Norwegian Sea

Although oceanic spreading is often perpendicular to the ridge trends, in some cases the angle between these two directions can be significantly less than 90 degrees (40 degrees-50 degrees). This occurs because of either a bend of the ridge trend or a change of the spreading direction. We here describe oblique spreading in the Mohns Ridge, resulting in deformation partitioning between the valley walls, which are dominantly affected by strike-slip displacements, and the axial valley which is subject to nearly pure extension. The axial valley walls are characterized by en echelon normal faults affecting the walls, while the axial valley is affected by parallel faults grouped into oblique sets. These fault sets define different structures, horst or tilted blocks, that are regularly spaced inside the axial valley. Moreover some ridge segments mainly undergo pure extension, whereas others are affected by oblique extension. We explain this faulting pattern, including the along-strike and transverse variations, as a consequence of depth variations of the brittle-ductile transition.