Seismic reflection profiles of the New Zealand plateau

Up to May 1966, about 15,000 km of reflection profiler data had been collected by Lamont Geological Observatory in New Zealand waters. They show that the Permo-Jurassic schists and graywackes of the Chatham rise can be traced northward beneath the Hikurangi trench and southward into the Bounty basin. These rocks may extend southeasterly into the deep sea. The schists and graywackes form the undermass of the Chatham rise (where they are probably capped by Eocene rocks) and of the Campbell plateau. The Southland syncline of South Island does not appear to project into the Bounty basin. The post Permo-Jurassic sediment cover thickens gradually toward the center of the basin and thins on the crest of the Chatham rise and along the southwest edge of the Campbell plateau. The sediments along the western lip of the Campbell plateau are tectonically distorted; elsewhere on the plateau they are relatively undisturbed and are about a kilometer thick. The large shelf between Lord Howe rise and Cook's strait is underlain by very thick, flat-lying sediments. The sediments on the Lord Howe rise, dated Eocene at one point, lie on an acoustically opaque undermass, having the appearance (in the profiler data) of the Chatham rise schists. The flat-lying sediments of the shelf are structurally separate from the rather deformed sediments on the rise. In marked contrast to the western shelf, the sediments of the eastern slope of North Island are complexly folded. A sediment-filled trough, evidently a southern extension of the Kermadec trench, defines a major tectonic boundary between the flat-lying sediments in the deep sea to the east and the intense folding to the west. A Cretaceous unconformity, recorded ashore, can be traced seaward almost to the filled trough. An outer ridge has formed seaward of the trough. The Hikurangi submarine canyon is diverted to the east and empties into the Pacific basin 250 miles east of North Island, where the sediments are nearly 2 km thick.