Neotectonics of the Macquarie Ridge Complex, Australia-Pacific plate boundary

New marine geophysical data along the Macquarie Ridge Complex, the Australi a-Pacific plate boundary south of New Zealand, illuminate regional neotecto nics. We identify tectonic spreading fabric and fracture zones and precisel y locate the Australia-Pacific plate boundary along the Macquarie Ridge Com plex. We interpret a similar to 5-10 km wide Macquarie Fault Zone between t he two plates along a bathymetric high that extends nearly the entire lengt h of the Australia-Pacific plate boundary south of New Zealand. We conclude that this is the active Australia-Pacific strike-slip plate boundary. Arcu ate fracture zones become asymptotic as they approach the plate boundary. A broad zone of less intense deformation associated with the plate boundary extends similar to 50 km on either side of the Macquarie Fault Zone. Marine geophysical data suggest that distinct segments of the plate boundary have experienced convergence and strike-slip deformation, although teleseismic evidence overwhelmingly indicates strike-slip motion along the entire surve yed boundary today. The McDougall and southernmost Puysegur segments show n o evidence for past underthrusting, whereas data from the Macquarie and Hjo rt segments strongly suggest past convergence. The present-day strike-slip plate boundary along the Macquarie Ridge Complex coincides with the relict spreading center responsible for Australia-Pacific crust in the region. Our conceptual model for the transition from seafloor spreading to strike-slip motion along the Macquarie Ridge Complex addresses the decreasing length o f spreading center segments and spacing between fracture zones, as well as the arcuate bend of the fracture zones that become asymptotic to the curren t transform plate boundary.