Perspectives on Cretaceous Gondwana break-up from detrital zircon provenance of southern Zealandia sandstones

Abstract

-Detrital zircon U-Pb ages in 37 sandstones from late Early -Late Cretaceous marine and non-marine successions across southern Zealandia indicate a provenance from local basement within present-day Zealandia. Samples from Taranaki Basin were derived from Median and Karamea batholith granitoids with transport directions from west to east. Samples from West Coast, Western Southland and Great South basins contain components derived more locally and more variably from Median Batholith and Rahu Suite granitoids and/or the Palaeozoic Buller Terrane. West Coast Basin samples have more plutonic contributions and Great South Basin localities have more Albian-aged (c. 110-100 Ma) zircons. Samples from Canterbury Basin were sourced from Torlesse Composite Terrane basement. The provenance variations are present in both marine and non-marine sandstones and suggest localized watersheds. This fits an interpretation of Late Cretaceous deposition in riftcontrolled basins across southern Zealandia during pre-Gondwana break-up regional extension. More speculatively, some additional source areas may have been created at the rifted margins of Zealandia during this break-up.

Reconnaissance Basement Geology and Tectonics of South Zealandia

“…Thirty zircon grains from Auckland Island granite sample OU21583 were analyzed by LA‐ICPMS at the University of Otago, but 14 were discarded due to >10% discordance, a result of especially high U contents, and one 947 Ma grain is inherited. The remaining 15 grains (Figure b) yield a weighted mean 206 Pb/ 238 U age of 95.6 ± 1.7 Ma (MSWD = 1.2), within error of the 95 ± 1 Ma age reported by Adams et al ().…”

“…Scott et al () and ^Adams et al (). The age for P28371 is considered the best age for Bounty Island granite.…”

“…Previous geochronological work on the Snares granite includes U‐Pb zircon ages of 109 ± 1.0 Ma (P63138; Scott et al, ) and 96 ± 5 Ma (5 grains from R10701; Adams et al, ) for a weakly deformed muscovite granite. We reinterpret the sparse data for sample R10701 given an MSWD of 13 and apparent discordance for one of two younger analyses and suggest an age of 99.3 ± 1.3 Ma, MSWD = 0.5).…”

“…Denison and Coombs () reported K/Ar ages of 93 and 97 Ma on muscovite from two different samples (recalculated using current decay constants) and Mortimer et al () reported a high‐quality 40 Ar/ 39 Ar muscovite isochron age of 99.5 ± 0.8 Ma, which they interpreted as the age at which the sample rapidly cooled through 350 ± 50 °C. From Auckland Island, Adams et al () reported a 95 ± 1 Ma U‐Pb zircon age for granite R24802. K/Ar biotite ages on unaltered samples are as old as 94–97 Ma (Adams, ; Denison & Coombs, ).…”

“…The small area of slightly older Broughton Granodiorite (114 Ma, Scott et al, ) on Snares Islands may, however, belong to the Rahu Suite. A third Snares age of 99.3 ± 1.3 Ma age (recalculated from Adams et al, ) indicates the presence of postsubduction age granitic rocks on Snares Islands.…”