Ridge Propagation and the Stability of Small Mid-Ocean Ridge Offsets

The mid-ocean ridge system comprises a series of spreading ridges, transform faults, propagating ridges, and other non-transform offsets. Transform faults remain stable for millions of years leaving long linear scars, or fracture zones, on older seafloor. Propagating ridges migrate in the ridge parallel direction leaving V-shaped or W-shaped scars on older seafloor. Vertical gravity gradient maps can now resolve the details of the ridge segmentation. For slow- and intermediate-spreading ridges, there appears to be an offset length threshold above which adjacent ridges do not propagate so remain as stable transform faults. We propose this threshold is due to the yield strength of the lithosphere, and we develop a model framework based on a force balance wherein forces driving propagation must exceed the integrated shear strength of the offset zone. We apply this model framework to 5 major propagating ridges, 55 seesaw propagating ridges, and 69 transform faults. The model correctly predicts the migration of 4 out of 5 major propagating ridges and the stability of transform faults, but the results for seesaw propagators are less accurate. Model predictions for direction of ridge propagation are mixed as well. This model framework simplifies deformation in the shear zone, but can possibly explain why non-transform deformation is preferred at short offsets.