Abstract: Volcanism of Late Cretaceous–Miocene age is more widespread across the Zealandia continent than previously recognized. New age and geochemical information from widely spaced northern Zealandia seafloor samples can be related to three volcanotectonic regimes: (1) age-progressive, hotspot-style, low-K, alkali-basalt-dominated volcanism in the Lord Howe Seamount Chain. The northern end of the chain ( c. 28 Ma) is spatially and temporally linked to the 40–28 Ma South Rennell Trough spreading centre. (2) Subalkaline, intermediate to silicic, medium-K to shoshonitic lavas of >78–42 Ma age within and near to the New Caledonia Basin. These lavas indicate that the basin and the adjacent Fairway Ridge are underlain by continental rather than oceanic crust, and are a record of Late Cretaceous–Eocene intracontinental rifting or, in some cases, speculatively subduction. (3) Spatially scattered, non-hotspot, alkali basalts of 30–18 Ma age from Loyalty Ridge, Lord Howe Rise, Aotea Basin and Reinga Basin. These lavas are part of a more extensive suite of Zealandia-wide, 97–0 Ma intraplate volcanics. Ages of northern Zealandia alkali basalts confirm that a late Cenozoic pulse of intraplate volcanism erupted across both northern and southern Zealandia. Collectively, the three groups of volcanic rocks emphasize the important role of magmatism in the geology of northern Zealandia, both during and after Gondwana break-up. There is no compelling evidence in our dataset for Late Cretaceous–Paleocene subduction beneath northern Zealandia. Supplementary material: Trace element compositions of zircons and whole-rock chemical compositions obtained by previous studies are available at: https://doi.org/10.6084/m9.figshare.c.3850975

Abstract The Reinga Basin occupies a northwest-southeast bathymetric d epression between the West Norfolk and Reinga ridges and has an area of about 100,000 sq. km. Rock samples have been dredged from surrounding ridges, but no boreholes have been drilled. We present a seismic stratigraphy developed using 5,135 line km of new 2D seismic-reflection data and 20,000 line km of older data, and we tie this stratigraphy to boreholes in the nearby Northland and Taranaki basins. We identify six phases of basin evolution. The first phase involved extension across northwest-trending normal faults. The region subsided passively during phase 2, and we infer from regional considerations that this phase lasted from Late Cretaceous until middle Eocene time. Phase 3 was late Eocene compression, which we interpret to be related to the initiation of the Tonga-Kermadec subduction. This led to uplift and erosion of the West Norfolk and Reinga ridges and deposition of detrital material at the center of the Reinga basin. Oligocene to early Miocene regional subsidence (phase 4) resulted in flooding of structures created during phase 3. Uplift of the Wanganella Ridge, in the northwest part of the Reinga Basin, occurred at the end of the early Miocene (phase 5). The last phase is tectonically passive, but with ongoing sedimentation up until the present day (phase 6). Upper Cretaceous units in the nearby Taranaki Basin contain coaly source rocks, and coal has been dredged from the ridge on the southwest margin of the Reinga Basin. Maturation models of three sites in the Reinga Basin predict that Cretaceous type III coaly source rocks within basal strata would begin to generate and expel petroleum in early Cenozoic time and expulsion would continue to the present day. The top of the oil expulsion window is modeled at 4.0 +/- 0.5 km below the sea bed, implying a potential kitchen area of approximately 15,000 sq km for Cretaceous source rocks, or a broader area if Jurassic source rocks are present. Most oil and gas expulsion is predicted to be later than the Eocene to Miocene folding and reverse faulting events that created structural traps. It is outside the scope of our study to develop play concepts or analyze direct hydrocarbon indicators, but our regional stratigraphic and tectonic study, combined with a consideration of petroleum system components that may be present, indicates that the Reinga Basin is prospective for oil and gas.