Abstract Finite-element models of continental rifting show that formation of non-volcanic rifted margins may be the result of extension of a rheologically homogeneous crust. In such circumstances lithosphere necking does not become well developed until late in the rift history, delaying the onset of decompression melting in the asthenosphere until the last 10% of the rifting episode. This result is robust over a broad range of mantle temperatures, margin geometries, and extension rates. A cool mantle is not required, so the models are able to account for the production of oceanic crust at the end of amagmatic rifting episodes. The duration of the syn-rift melting episode is most sensitive to changes in extension rate, with higher extension rates leading to shorter periods of melt production. The duration of the rifting episode is controlled by extension rate and initial crustal thickness, and the geometry of the margin after continental break-up is controlled by initial crustal thickness and the distribution of pre-existing rheological heterogeneity in the crust. The model results are generally compatible with the dimensions and extension rates of rifted continental margins across the globe, and provide a particularly good fit to the evolution of the Iberia Abyssal Plain margin.

Abstract The active margin of Gondwana is presently preserved in the southwest Pacific region in the formerly continuous Gondwana fragments of Australia, Antarctica and New Zealand. The Phanerozoic tectonic history of New Zealand is interpreted in terms of progressive Pacific-ward growth by accretion of arc-trench systems and the basement rocks are described in terms of a number of volcano-sedimentary accreted terranes, suites and batholiths that intrude the terranes. The age of these basement rocks ranges from Early Cambrian to late Early Cretaceous. The origin of the magmatic and sedimentary rocks and the time of accretion of the New Zealand terranes to the Gondwana margin are important for the understanding of Phanerozoic Pacific tectonics. Geochronological research over the last decade on igneous rocks and conglomeratic units shows that the Tutoko Complex/Amundsen Province plutons are major contributors of detritus to the Pahau depositional basin and that the Antarctic sector of the Panthalassan Gondwana margin has to be (re)considered as the likely source for the Permo-Triassic Rakaia sediments. Igneous clast data have greatly improved understanding of the evolution of the New Zealand microcontinent and have put tighter constraints on its Mesozoic tectonic setting within the southwest Pacific margin of Gondwana.