Late Cretaceous-Cenozoic tectonic development of the southwest pacific region

Abstract

A new model of the plate tectonic development of the southwest Pacific integrates the continental geology of New Zealand with the age structure of the surrounding oceanic crust revealed previously from magnetic anomaly lineations. The model differs from previous ones in that the onland geology of New Zealand is used to constrain the tectonic development in two important ways: (1) the modern Australia-Pacific plate boundary did not transect the New Zealand sector until 23 million years ago; (2) there has been a total of only c.500 km of dextral displacement on the plate boundary through New Zealand. The model is described with reference to a series of paleotectonic maps drawn to represent the setting at the times of anomalies 32, 24, 7 and 5. Novel interpretations based on these reconstructions include the following. During the late Cretaceous the Campbell Fault was a continental transform fault between the Tasman Sea spreading centre and the Bounty Rift, its 330 km of dextral displacement accompanying 25° of counterclockwise rotation of a Campbell Plateau block. When the eastward-propagating Southeast Indian Ridge broke into the south Tasman Sea 57 million years ago, it continued to propagate directly into southern South Island, and generated late Eocene-Oligocene continental rifting through western New Zealand. At the same time, back-arc spreading in the Norfolk Basin caused continental rifting along a similar trend in western North Island. The Australia-Pacific plate boundary originated as a transform fault between the Southeast Indian Ridge and the pre-existing Kermadec Trench. It developed in response to the sudden cessation of spreading on the segment of the Southeast Indian Ridge east of a fracture zone here named Fracture Zone Z. Two implications arise from this model regarding the integrity of Antarctica: 1. (1) during the Cretaceous, Marie Byrd Land was probably no more than 200 km northwest of its present position; 2. (2) the proposition made in some earlier plate tectonic reconstructions, that if the Alpine Fault did not form until after the late Eocene there must be a late Cretaceous-early Tertiary plate boundary within Antarctica, is most probably valid.