HR: 0800h
AN: T41C-1214    [Abstracts]
TI: Association between collision, microplate rotation, and back-arc rifting at obliquely convergent margins in the western Pacific: New insights from geodetic data
AU: * Wallace, L
EM: l.wallace@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: McCaffrey, R
EM: mccafr@rpi.edu
AF: Dept. of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 8th St., Troy, NY 12180-3590 United States
AU: Beavan, J
EM: j.beavan@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Ellis, S
EM: s.ellis@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AB: We present results from kinematic modelling of geodetic data from two obliquely convergent margins in the western Pacific (Papua New Guinea and the North Island, New Zealand). In each of these plate boundary zones, microplates rotate rapidly (3-8 degrees/Myr) relative to the bounding Australian and Pacific plates. These rapid microplate rotations cause dramatic along-strike changes in plate boundary deformation type and rate, and are associated with back-arc rifting in the Manus Basin and the Taupo Volcanic Zone. The rotation of the eastern North Island of New Zealand (NZ) also accommodates much of the margin-parallel component of relative motion that must be taken up in the plate boundary zone, and therefore contributes to the process of slip partitioning. The South Bismarck microplate in Papua New Guinea (PNG), and the eastern North Island of NZ each have angular velocity vectors describing their motion (relative to the subducting plate) that intersect the surface of the Earth where buoyant features (e.g., a continental fragment, oceanic plateau or seamount chain) are colliding with the New Britain Trench (PNG) and the Hikurangi Trough (NZ). We suggest that it is the change from collision to subduction along the obliquely convergent plate margins that causes the rapid microplate rotation and subsequent back-arc rifting in NZ and PNG. At other Western Pacific convergent margins where buoyant indentors subduct and back-arc rifting occurs (Marianas, Vanuatu, and Tonga), our modeling results are very similar to the PNG and NZ cases, in that microplates rotate rapidly about the point where a buoyant indentor intersects the margin. The coincidence of microplate rotations and back-arc rifting with collision of buoyant features at subduction margins suggests there may be a causal relationship between these phenomena. A possible explanation is that the change from collision-related forces to subduction-related forces along the plate boundary exerts a torque on the forearc microplate. This torque causes the plate boundary zone microplates to rotate rapidly about a point (relative to the subducting plate) where the collisional resistance forces are highest.
DE: 8107 Continental neotectonics
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
DE: 1206 Crustal movements--interplate (8155)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting