ABSTRACT
New Zealand is the subaerial remnant (~10%) of an otherwise submerged block of continental crust, the New Zealand Plateau (Farquhar, 1906) or Zealandia (Mortimer and Campbell, 2014). The continent is well defined by the 2000 and 2500 m isobaths and extends from the subantarctic islands to New Caledonia (Figure 3.1). This large block straddles the active margin between the Indo-Australian and Pacific plates. (In the figure, the barbs along the subduction zones are on the overriding plate and the points on the barbs indicate the direction of subduction beneath it.) The Indo-Australian plate is moving northward, and the Pacific plate is moving eastward. The New Zealand part of the plate margin comprises two subduction zones of opposite polarity, the Hikurangi margin in the north and Puysegur-Fiordland margin in the south. These are connected by a transform fault system made up of the Alpine fault zone and the Marlborough fault system. Subduction of the Pacific plate beneath the North Island terminates at the southern end of the Hikurangi Trough, where the thick continental crust of the Chatham Rise intersects the margin. (See the “Glossary of geological terms” for definitions of “subduction,” “transform fault,” and others.)
The migration of subduction zones is one of the most important processes in southwest Pacific tectonics. Figure 3.1 shows the series of basins that have opened behind the Australia/Pacific plate margin as this has migrated eastward into the Pacific. Reading from the oldest to the youngest, these are the Tasman, South Loyalty, Coral Sea, New Caledonia, North Loyalty, South Fiji, North Fiji, and Lau basins.
