Evolution of rifted ocean ridges

A major question in seafloor tectonics has been, how does the 2-km-deep rift valley characteristic of slow-spreading ridges evolve into the relatively horizontal undulating relief of the rift mountains? Deep-tow studies of the Mid-Atlantic Ridge suggest that the primary mechanism for transformation of the rift valley topography is normal faulting along fault planes which dip away from the valley axis. The faulting occurs in a narrow zone just beyond the outer walls of the rift valley. This model allows for a steady-state evolution of the rift valley into the rift mountains in which the state of stress in the oceanic lithosphere continues to be in horizontal deviatoric tension throughout the entire process. Alternate mechanisms involving reverse faulting or regional tilt may be active but are found to be of less importance. Implications for various dynamic models of the rift valley are discussed.