DEFORMATION PARTITIONING IN A SLOW-SPREADING RIDGE UNDERGOING OBLIQUEEXTENSION - 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 significa ntly 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 dire ction. We here describe oblique spreading in the Mohns Ridge, resultin g in deformation partitioning between the valley walls, which are domi nantly affected by strike-slip displacements, and the axial valley whi ch is subject to nearly pure extension. The axial valley walls are cha racterized 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 ridg e 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 vari ations of the brittle-ductile transition.