Extension of Delamerian (Ross) orogen into western New Zealand: Evidence from zircon ages and implications for crustal growth along the Pacific margin of Gondwana

Ion-microprobe zircon U/Pb age data are presented for two metasedimentary sequences in Fiordland, New Zealand: one is a correlative of the Lachlan fold belt in southeast Australia and incorporates metamorphosed Ordovician turbidites intruded by 350 370 Ma S-type granites, and the other is equivalent in age to the older Delamerian fold belt and is derived from Cambrian-Ordovician protoliths (Kanmantoo Group) intruded by 480 Ma granitic orthogneiss. The latter was exhumed from lower crustal depths and is considered to be representative of basement not only in New Zealand but also in the formerly contiguous regions of southeast Australia and Antarctica. This basement underwent melting and low-pressure high-temperature metamorphism at 350 370 Ma and yields detrital zircon with ages identical to those of inherited zircon in the mid-Paleozoic S-type granites.