HR: 11:50h
AN: T12C-07    [Abstracts]
TI: Tectonic evolution of the Resolution Ridge System, New Zealand: insights gained through UNCLOS surveying for natural prolongation
AU: * Wood, R
EM: r.wood@gns.cri.nz
AF: GNS Science, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Barker, D
EM: d.barker@gns.cri.nz
AF: GNS Science, PO Box 30368, Lower Hutt, 6009 New Zealand
AB: For coastal States, demonstration of submerged natural prolongation of the land mass is a key element in delimiting the extent of the continental margin under the terms of UNCLOS article 76. Straddling an active plate boundary and with continental margins encompassing most major tectonic settings, the New Zealand (NZ) continent presents numerous, varied examples of natural prolongation of the land mass. The mostly submerged NZ continent covers over 5,000,000 km2. The continent grew by the accretion of basement terranes and the Hikurangi Plateau, a large igneous province, along the eastern margin of Gondwana during the Paleozoic and Mesozoic. Fragmentation of Gondwana initially involved thinning and extension of the continental rocks of New Zealand, and ultimately resulted in the separation of the New Zealand continent from Australia and Antarctica. Renewed tectonic activity in the Cenozoic resulted in the formation of the Resolution Ridge System (RRS) southwest of NZ and several volcanic arcs north of NZ. These volcanic arcs extend onto NZ and are a submerged natural prolongation of the land mass. Geological and geophysical surveys undertaken for the NZ Continental Shelf Project established that most of the RRS was not a prolongation of the NZ land mass, and advanced understanding of NZ's tectonic evolution. The RRS is a series of bathymetric highs extending southwest of Fiordland, NZ, from Resolution Ridge itself, adjacent to the northern limit of the Puysegur Trench, to the southeast termination of the fossil spreading centre in the Tasman Sea (TS; 158°40'E, 48°10'S). A 40° bend at 162°E, 46°30'S divides the ridge system into a northeastern segment, comprising large, en echelon, northeast-southwest-trending basement ridges and basins, and a southwest segment composed of longer, more continuous ridges trending northeast-southwest. The ridge system was formed by rapid reorientation of seafloor spreading directions (through c. 90°) in the TS at ~50 Ma. The younger oceanic rift initiated along the Campbell Plateau margin and propagated northward into continental NZ. Seafloor spreading in this orientation was maintained between about 47 and 30 Ma (anomalies 21-11) to form the Southeast Tasman Oceanic Crust (STOC). Integration of swath bathymetry, seismic reflection, potential field, and dredge data confirms the origin of the ridge system as an uplifted rift flank formed in oceanic crust in the southwest, and establishes the probable extent of fragments of continental crust in the northeast. The initial rift exploited existing faults and TS crustal structure, and the inherited nature of these faults along the ridge system may provide a rationale for its rapid formation. A deep basement trough lies between the uplifted rift flank footwall and the younger STOC oceanic basement. This trough follows the trend of the RRS, paralleling the basement ridges of the southwest RRS and truncating the southern extent of the en echelon ridges of the northeast RRS. This implies rapid faulting across pre-existing northeast-southwest structural grain and an apparent delay in onset of magmatic systems associated with newly established sea floor spreading. There is no evidence of significant structural reactivation post-dating formation of the RRS. More precise identification of TS transform structures along the ridge system provides pinning points that may help better constrain plate reconstructions and the processes of rift propagation during STOC sea floor spreading.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology, geology, and geophysics
SC: Tectonophysics [T]
MN: Fall Meeting 2005