Early Cretaceous greywacke from Colville Knolls, New Zealand

Blocks of greywacke sandstone were dredged from the Colville Knolls, on the margin of the Zealandia continent, in 1989. Re-examination shows them to be quartz-poor feldspathic litharenites similar to those recorded from the basement, rather than sedimentary cover, of the North Island. U-Pb dating of detrital zircons reveals significant age populations at 107, 115, 122, and 245 Ma. These compositions and ages best match those of Waipapa Composite Terrane greywacke basement on nearby Great Barrier Island. As such, an earlier Waipapa correlation is preferred, but Colville Knolls detrital petrography and zircon ages also resemble those from some Early Cretaceous Torlesse Composite Terrane greywackes. Irrespective of terrane correlation, Colville Knolls is a submarine outcrop of Cretaceous greywacke deposited at the toe of the Gondwana Mesozoic accretionary wedge, and likely represents the outer, northeastern margin of Zealandia continental crust.