We report new U-Pb zircon ages, geochemical and isotopic data for Mesozoic igneous rocks, and new seismic interpretations of mostly submerged South Zealandia (1.5 Mkm 2 ). We use these data, along with existing geological and geophysical data sets, to refine the extent and nature of geological units. Our new 1:25 M geological map of South Zealandia provides a regional framework to investigate the rifting and breakup that formed Zealandia, Earth's most submerged continent. Samples of prerift (pre-100 Ma) plutonic rocks can be matched with on-land New Zealand igneous suites and indicate an east-west strike for the subduction-related 260 to 105-Ma Median Batholith across the Campbell Plateau. The plutonic chronology of formerly contiguous plutonic rocks in West Antarctica reveals similar pulses and lulls to the Median Batholith. Contrary to previous interpretations, the Median Batholith does not coincide with the 1,600-km-long Campbell Magnetic Anomaly System. Instead we interpret the continental magnetic anomalies to represent a mainly mafic igneous unit, whose shape and extent is controlled by synrift structures related to Gondwana breakup. Correlatives of some of these unsampled igneous rocks may be exposed as circa 85 Ma alkalic volcanic rocks on the Chatham Islands. Extension directions varied by up to 65°from 100 to 80 Ma, and we suggest this allowed this large area to thin considerably before final rupture to form new oceanic crust. Synrift (90-80 Ma) structures cut the oroclinal bend in southern South Island and support a pre-early Late Cretaceous age of orocline formation.

The Great South Basin (GSB) developed in the Cretaceous from continental rifting at the southeastern margin of Gondwana. The basin contains a thick Cretaceous succession that is largely unaffected by Neogene compressional tectonics, with rift faults and associated growth strata imaged by good-quality 2-D and 3-D seismic data tied to wells. These data show three distinct stages of normal faulting here referred to as fault system initiation (Stage 1), fault system growth (Stage 2), and fault system death (Stage 3). The different stages of fault system evolution comprise dominant NE trending faults (NW-SE extension), and minor NW trending faults (NE-SW extension). Fault initiation at~105-101 Ma mainly occurred in the central GSB with rift depocenters mostly on, or close to, NW trending basement terrane boundaries. These preexisting basement boundaries represent zones of weakness that locally promoted early localization of NW faults and retarded the propagation of NE faults. With increasing regional extension and fault system growth from~101 to 90 Ma the influence of the basement fabric gradually decreased, while NE trending faults increased in length, number, displacements, and spatial distribution. Finally, during the fault system death stage from~90 to 83 Ma the length, number and displacements of faults decreased. Fault death coincided in time with Gondwana breakup and reflects the localization of extension along spreading centers distal to the GSB.

The Great South Basin, off New Zealand’s southeast coast, has attracted renewed exploration interest from major petroleum companies since 2005. The distribution of the mid Cretaceous to Paleocene source rocks (coals and coaly mudstones) is a critical component in evaluating basin prospectivity. This paper delineates source rock distribution from seismic facies characterisation, and presents a series of updated paleogeographic maps over the initial (Cretaceous) phases of basin evolution. Basin evolution has been analysed from mapped sequence stratigraphic boundaries and isochron maps. Seismic facies were characterised based on the amplitude, continuity, and stacking pattern of the reflection packages. The identified facies were calibrated with well data for age, gross lithology, and gross depositional environment. Areas of source rock deposition were demarcated using seismic attribute interval maps, from which a series of updated paleogeographic maps was prepared. Four second-order sequences have been identified within the Cretaceous succession. The lower two sequences are mainly fault bounded and were deposited in a syn-rift phase. In contrast, the upper two sequences reflect a change in basin character from rifting to a post-rift thermal sag phase. Source facies within both the syn- and post-rift sequences were deposited in mainly non-marine to marginal marine settings, although there is also the possibility of lacustrine source rocks in isolated syn-rift depocentres. The wide geographic spread of source rock intervals within the Cretaceous sequences allows for a variety of petroleum generation and exploration play scenarios.

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