KINEMATICS OF OVERLAPPING RIFT PROPAGATION WITH CYCLIC RIFT FAILURE

Existing kinematic models for propagation of oceanic spreading ridges that incorporate overlap between ridge segments fail to describe detailed observations of the failed segments. I present a new model which discards the assumption of steady state behavior of the failing rift, permitting inward curvature of both rift tips in the overlap region. The shape of an inward-curving failing rift must continuously change, but is assumed to cyclically return to its original shape by discrete inward ridge jumps. Other assumptions of symmetric spreading and uniform simple shear deformation between the overlapping rift tips are retained from previous models. Inward curvature of failed rift structures provides much better agreement with observations, and is consistent with tensile fracture theory. If the offset between ridge segments is small enough, the inward jumps of the failing rift will cut across deformed structures originally formed at the propagating tip, possibly generating seafloor fabrics that crosscut each other at nearly right angles. Observations of such structures near the Gorda Ridge can be explained by a model incorporating variable cyclicity of the failing rift. © 1990.