HR: 10:35h
AN: T41F-02 INVITED
TI: Subduction Initiation Along the Macquarie Ridge Complex?
AU: * Coffin, M F
EM: mikec@ig.utexas.edu
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AU: Meckel, T P
AF: Dept. of Geological Sciences, University of Texas at Austin, Austin, TX, United States
AU: Meckel, T P
AF: Institute for Geophysics, The University of Texas at Austin, Austin, TX, United States
AU: Mosher, S
AF: Dept. of Geological Sciences, University of Texas at Austin, Austin, TX, United States
AU: Mosher, S
AF: Institute for Geophysics, The University of Texas at Austin, Austin, TX, United States
AU: Massell, C
AF: Scripps Institution of Oceanography, University of California-San Diego, La Jolla, CA, United States
AU: Daczko, N
AF: Dept. of Geological Sciences, University of Texas at Austin, Austin, TX, United States
AU: Daczko, N
AF: Institute for Geophysics, The University of Texas at Austin, Austin, TX, United States
AU: Wertz, K
AF: Dept. of Geological Sciences, University of Texas at Austin, Austin, TX, United States
AU: Wertz, K
AF: Institute for Geophysics, The University of Texas at Austin, Austin, TX, United States
AU: Bernadel, G
AF: Australian Geological Survey Organisation, Canberra, ACT, Australia
AU: Symonds, P
AF: Australian Geological Survey Organisation, Canberra, ACT, Australia
AB: The Macquarie Ridge Complex (MRC) extends for ca. 1500 km between New Zealand's South Island and the Indian-Antarctic-Pacific triple junction, and comprises the boundary between the Australian (Indian) and Pacific plates. Motion along this boundary has changed from divergence to dominantly strike slip, with areas of transpression and transtension, since ca. 10 Ma. The arcuate MRC displays unique bathymetry among submarine ridges worldwide, with four distinct segments (from north to south, Puysegur, McDougall, Macquarie, and Hjort) characterized by alternating ridge-trough polarity. A major fault zone on the crest or flank of the bathymetric ridge is continuous along the entire length of the MRC. Intermediate depth earthquakes, compressional focal mechanisms, and a single, small calc-alkaline volcano (Solander Island) suggest that subduction may be initiating in southernmost New Zealand (Fiordland) and the Puysegur region. Marine geophysical data show one or more major thrust faults along the Puysegur trough in addition to the strike slip fault along the Puysegur ridge, implying strain partitioning. The McDougall and Macquarie segments are characterized by shallow focus earthquakes and strike slip focal mechanisms; the ridges and troughs may be explained by past thrust faulting, but any evidence for subduction or initiation thereof is absent. In the Hjort region, a well-developed trench complements the crestal fault zone, again implying strain partitioning, although all earthquakes appear to be shallow. Unsampled seamounts paralleling the Hjort trench and ridge may be related to subduction, or may have been produced by hotspot activity. The morphology of the MRC integrates the changes in relative motion between the Australian (Indian) and Pacific plates since ca. 10 Ma, and the MRC presents a case study for possible models of subduction initiation.
DE: 0930 Oceanic structures
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
DE: 8000 STRUCTURAL GEOLOGY
DE: 8150 Plate boundary--general (3040)
SC: T
MN: 2001 AGU Fall Meeting