Ridge reorientation mechanisms: Macquarie Ridge Complex, Australia-Pacific plate boundary

The Macquarie Ridge Complex portion of the Australia-Pacificplate boundary south of New Zealand provides a unique, completerecord of a 60°-90° change in spreading directionsince 40 Ma that resulted in the transition from a spreadingcenter to a transform plate boundary. Marine geophysical datashow that during reorientation, most ridge segments completelydisappeared and all shortened. Additionally, modification ofnewly created crust caused differences in widths of correlativespreading segment corridors on the two plates. We propose twomodels for ridge reorientation that explain the observed spreadingfabric and arcuate fracture zone relationships. Nonrigid platedeformation was accommodated by failing and propagating spreadingridge segments (rifts) and transfer of crust between platesduring the gradual reorientation of the spreading axes.