The mid-Cretaceous transition from basement to cover within sedimentary rocks in eastern New Zealand: evidence from detrital zircon age patterns

Detrital zircon U-Pb ages for 30 Late Jurassic and Cretaceous sandstones from the Eastern Province of eastern New Zealand, combined with previously-published geochronological and palaeontological data, constrain the time of deposition in the Pahau and Waioeka terranes of the Cretaceous accretionary margin of Zealandia, and their adjacent cover strata. The zircon age patterns also constrain possible sediment source areas and mid-Cretaceous geodynamic models of the transition from basement accretionary wedge to passive-margin cover successions. Pahau Terrane deposition was mainly Barremian to Aptian but continued locally through to late Albian time, with major source areas in the adjacent Kaweka and Waipapa terranes and minor inputs from the inboard Median Batholith. Waioeka Terrane deposition was mainly Albian, with distinctive and exclusive sediment sources, principally from the Median Batholith but with minor inputs from the Western Province. Alternative tectonic models to deliver such exclusive Median Batholith and Western Province-derived sediment to the mid-Cretaceous Zealandia continental margin are: (1) the creation of a rift depression across Zealandia or (2) sinistral displacement of South Zealandia with respect to North Zealandia, to expose Western Province rocks directly at the Zealandia margin. Detrital zircon age patterns of Cretaceous cover successions of the Eastern Province of eastern New Zealand demonstrate purely local sources in the adjacent Kaweka and Waipapa terranes. Cretaceous zircon components show a decline in successions of late Early Cretaceous age and disappear by late Late Cretaceous time, suggesting the abandonment or loss of access to both the Median Batholith and Western Province as sediment sources.