Systematics of ridge propagation south of 30°S

Abstract

New high-resolution Geosat altimetry data south of 30°S reveal numerous propagating ridge wakes along intermediate- and slow-spreading ridges. These new examples provide a large enough database to establish systematics of ridge propagation. Almost all active propagating ridges propagate down a regional along-axis gravity or bathymetry gradient. The sense of the propagating ridge offset (right lateral vs. left lateral) is related to recent changes in spreading direction. We find there is a significant difference between the propagation of ridges with an axial high morphology which propagate at greater than ∼ 50% of their full-spreading rate and ridges with a median valley morphology which usually propagate at ∼ 25% of their spreading rate. The axial high propagators leave behind an asymmetric wake; the outer pseudofault appears as a continuous linear trough/step while the sheared zone appears as a chain of small gravity bumps. While we clearly see the propagating ridge wakes from offsets greater than ∼ 10 km at slow- and intermediate-spreading ridges, at ridges spreading faster than ∼ 75 mm/yr the amplitude of the wake topography decreases to the point where we no longer see these wakes in Geosat altimetry data. The systematics seen in this new data set support a fracture mechanics model for the dynamics of ridge propagation.