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

¹ Department of Geological Sciences, Jackson School for Geosciences, University of Texas, Austin, Texas 78712, USA
² Scripps Institution of Oceanography, 9500 Gilman Drive, MC0220, La Jolla, California 92093, USA

The Macquarie Ridge Complex portion of the Australia-Pacific plate boundary south of New Zealand provides a unique, complete record of a 60°–90° change in spreading direction since 40 Ma that resulted in the transition from a spreading center to a transform plate boundary. Marine geophysical data show that during reorientation, most ridge segments completely disappeared and all shortened. Additionally, modification of newly created crust caused differences in widths of correlative spreading segment corridors on the two plates. We propose two models for ridge reorientation that explain the observed spreading fabric and arcuate fracture zone relationships. Nonrigid plate deformation was accommodated by failing and propagating spreading ridge segments (rifts) and transfer of crust between plates during the gradual reorientation of the spreading axes.

Key Words: spreading center • Macquarie Ridge • rift propagation • ridge reorientation • transform • plate boundary