HR: 0830h
AN: T21C-0461    [PDF]
TI: Convergence history, topography, and early structural evolution of an obliquely convergent oceanic plate boundary: central and southern Macquarie Ridge Complex, Southwest Pacific
AU: * Meckel, T A
EM: tameckel@colby.edu
AF: Colby College, Department of Geology 5803 Mayflower Hill, Waterville, ME 04901-8858 United States
AU: * Meckel, T A
EM: tameckel@colby.edu
AF: Department of Geological Sciences, Jackson School of Geosciences The University of Texas at Austin, Austin, TX 78712-1101 United States
AU: * Meckel, T A
EM: tameckel@colby.edu
AF: Istitute for Geophysics, Jackson School of Geosciences The University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Mann, P
EM: paulm@ig.utexas.edu
AF: Istitute for Geophysics, Jackson School of Geosciences The University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Mosher, S
EM: mosher@mail.utexas.edu
AF: Department of Geological Sciences, Jackson School of Geosciences The University of Texas at Austin, Austin, TX 78712-1101 United States
AU: Coffin, M F
EM: mcoffin@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, Tokyo, 164-8639 Japan
AU: Symonds, P A
EM: Phil.Symonds@ga.gov.au
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AU: Bernardel, G
EM: George.Bernardel@ga.gov.au
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AB: Deformation along the Australian-Pacific transpressional plate boundary south of New Zealand (Macquarie Ridge Complex - MRC) since 5.9 Ma (anomaly 3Ay) has been accommodated by vertically displaced crust and variable amounts of strike slip faulting and/or underthrusting. Variable convergent histories result from the interplay of the close proximity of a drifting pole of rotation and the curvilinear trace of the plate boundary fault. We apply geomorphologic techniques to swath bathymetry data to quantify the amount of interplate deformation along three, distinctly oriented, 300-350-km long segments of the plate boundary since 5.9 Ma. Between $51\deg$S and $61\deg$S we calculate volumes of crust within 70 km of the plate boundary that are vertically displaced from the average seafloor depth occurring beyond the zone of active deformation. These volumes are compared to: (1) variable convergence angles, (2) the cumulative amount of perpendicular convergence predicted by stage pole rotations, and (3) active faulting at the seafloor in order to characterize the geodynamic evolution of the three different regions. Displaced volumes (anomalously shallow and deep bathymetry) adjacent to the plate boundary are proportional to the cumulative amount of plate boundary-normal convergence since 5.9 Ma. We integrate our results with four gravity transects across the central and southern MRC, illustrating the lithospheric-scale morphologic and structural evolution as underthrusting initiates at this obliquely convergent oceanic plate boundary. Along-strike morphologic changes in the MRC can be attributed primarily to the variable angles of convergence since 5.9 Ma. A convergence angle of $\sim$$25\deg$ marks the transition from strike-slip dominated faulting and large displaced crustal volumes to partitioned underthrusting and strike-slip faulting, and relatively low displaced volumes. Regions where convergence angles have not exceeded $25\deg$ correspond to significant bathymetric troughs, representing failed attempts to develop thrust faults. Active thrust faults and deeper bathymetric trenches occur where convergence has been $>$$25\deg$ since 5.9 Ma. Thus the MRC can be used to help constrain some of the convergence characteristics necessary for establishing underthrusting at obliquely convergent oceanic lithosphere settings.
DE: 3010 Gravity
DE: 3045 Seafloor morphology and bottom photography
DE: 7218 Lithosphere and upper mantle
DE: 8150 Plate boundary--general (3040)
DE: 8158 Plate motions--present and recent (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting