HR: 1340h
AN: T23B-1422    [Abstracts]
TI: Intraplate Deformation Adjacent to the Macquarie Ridge South of New Zealand - The Tectonic Evolution of a Complex Plate Boundary
AU: * Hayes, G P
EM: ghayes@geosc.psu.edu
AF: Geodynamics Research Group, Penn State University, 542 Deike Building, University Park, PA 16802, United States
AU: Furlong, K P
EM: kevin@geodyn.psu.edu
AF: Geodynamics Research Group, Penn State University, 542 Deike Building, University Park, PA 16802, United States
AB: The response of lithospheric plate boundaries to rapid changes in plate motions provide constraints used to determine the manner in which transitions in plate motions and plate boundary configurations can occur. In the case of the Australia – Pacific plate boundary in the Macquarie Ridge region south of New Zealand a substantial change in plate motions has occurred since the Oligocene. Over a period of less than 15Ma, this boundary changed from mid-ocean ridge spreading to simple translation, the record of which is recorded in the fabric and fracture zones of the oceanic lithosphere. Application of available well-constrained plate motions imply that substantial deformation of the oceanic lithosphere must have occurred after fracture zone formation to create the arcuate structure of these fracture zones today. Plate reconstructions of this plate boundary system from the Oligocene through the Early-Mid Miocene are used here to isolate the timing of transitions in plate motion from divergence to translational motion. These reconstructions identify rapid rotations in plate motions after approximately 25Ma. By 20Ma, the majority of crust created along this plate boundary was already in place, and the Australian Plate was translating northwards relative to the Pacific towards New Zealand, where a corner of Australian Plate is ultimately subducted. The timing of this transition in plate motions implies that the onset of subduction at the Puysegur Trench may have been as early as approximately 20Ma. These reconstructions also identify the shape of fracture zones either side of the relic mid-ocean ridge through the time of their formation. Comparison of these restored fracture zones with their present-day appearance delineates a broad zone of deformation extending ~150km into the plate interior from the Macquarie Ridge Complex, the modern plate boundary structure. This area of deformation coincides with a broad distribution of seismicity in the Australian Plate on both inter- and intra-plate structures, including two great (M8+) earthquakes over the past twenty years, one of which occurred over 130km from the plate boundary. The persistence of this deformation through time indicates a link with the evolution of the plate boundary from divergence to translation and subduction, and may be a result of stress build-up within the Australian Plate as a consequence of the impingement of the subducting plate on the thickened lithosphere of southern New Zealand. Such a collision may act as a resisting force to subduction, and if it continues, further deformation internal to the Macquarie Block may lead to a southward migration of the Australia:Pacific subduction interface and the capturing of this section of lithosphere onto the Pacific Plate.
DE: 3039 Oceanic transform and fracture zone processes
DE: 7220 Oceanic crust
DE: 8157 Plate motions: past (3040)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting