Topography and tectonics at the intersections of fracture zones with central rifts

Deep troughs with up to 2 km of relief occur at intersections of fracture zones with the central rift of mid-ocean ridges. The cause of these depressions may be the loss of hydraulic head due to the viscosity of the material that upwells passively at ridges to produce a new sea floor. At such intersections the transform fault truncates the central rift, imposing an additional boundary to which the upwelling material tends to stick. More head loss and, therefore, a deeper rift are required for the material upwelling near the fault. Atlantic fracture zones may obtain their topography through a partial locking of the trough into the spreading sea floor. Pacific fracture zones have been affected by changes in spreading direction. Since a transform fault offsetting a rifted ridge may leak, more mapping is required to determine the principal cause of Atlantic fracture zones.