Abstract

Single-crystal 40Ar/39Ar ages of detrital micas from Greenland Group (Ordovician) low-grade metagraywackes of the West Coast, South Island, New Zealand, indicate a source area having muscovite age patterns of 490–515 Ma. The detrital muscovite ages are characteristic of granitoid and gneiss terranes of the Ross-Adelaide fold belt of Antarctica; therefore, the source area for the Greenland Group sedimentary rocks was the immediately adjacent Pacific margin of Gondwana.

Similar age determinations for Rakaia terrane (Permian–Triassic) Torlesse Supergroup metagraywackes of the Wellington and Canterbury regions of New Zealand indicate that their source area included rocks having prominent muscovite cooling ages populations of 210–290 Ma (80%) and 410–460 Ma (15%). The Torlesse detrital muscovite age data thus suggest that the source area of the metagraywackes was not within the Lachlan fold belt of southeast Australia and analogues in Antarctica, nor in the adjacent Ross-Adelaide fold belt. Rather, the Rakaia terrane of the Torlesse metagraywackes is a true suspect terrane derived from a source area within the Hunter-Bowen fold belt of northeast Australia and the immediately adjacent older orogens of eastern Queensland.

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