HR: 0800h
AN: T41A-1159    [Abstracts]
TI: The Wishbone Ridge
AU: * Davy, B W
EM: b.davy@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6315 New Zealand
AB: The Wishbone Ridge gravity lineation appears on global gravity maps as the left-most branch of a series of forked gravity anomaly lineations which extend c. 1300 km from the Osbourn Trough at 25 degrees S to the Chatham Rise at 43 degrees S. The northeast trending gravity lineation forms a c. -40 mgal gravity anomaly southwest of the lineation intersection with Louisville Ridge at 39 degrees S. It also coincides with a bathymetric ridge rising up to 2 km above the neighbouring seafloor and extending from the Chatham Rise as far north as 40.3 degrees S. Swath bathymetry surveying indicates the bathymetric ridge is comprised of a series of southeast facing, tilted, en-echelon fault-blocks. Seismic reflection profiling across the south-eastern extension of the lineation reveal this tilted block structure extending south-westwards beneath the north-eastern crest of the Chatham Rise. The extent and continuity of the gravity lineation suggests the lineation marks a major crustal boundary. The tilted en-echelon blocks of the bathymetric ridge are suggestive of an extensional-strike slip fault. Seismic reflection profiling across the lineation north of its bathymetric exposure illustrates a major contrast in character and depth of the oceanic crust either side of the lineation consistent with transverse displacement along the lineation boundary. The northeast trend of the Wishbone lineation is mirrored in parallel volcanic ridges on the adjacent Hikurangi Plateau LIP and on the oceanic crust further north as well as in offsets of the Louisville Seamount trend. Offsets in the eastern Chatham Rise bathymetry also mirror this widespread trend suggesting motion along the Wishbone lineation may have originally broken through the Cretaceous North Chatham Rise Gondwana convergent margin forming the location for subsequent New Zealand-Antarctic rifting.
DE: 8110 Continental tectonics--general (0905)
DE: 8150 Plate boundary--general (3040)
DE: 8157 Plate motions--past (3040)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting