Recognition of mid-Paleozoic volcanism in New Zealand

摘要

Two felsic volcanic clasts from conglomerates in Fiordland and northwest Nelson provide U-Pb zircon ages of 359 and c. 362 Ma respectively; ages that occur within the interval between voluminous Western Province plutonic S-type magmatism of the Karamea and Ridge suites. Both volcanic clasts have inherited zircon populations, and trace element signatures suggesting derivation from crustal melts. The dacitic clast from the mid-Cretaceous Seek Cove Formation in southwest Fiordland has whole-rock chemistry and an O-Hf-zircon isotopic signature consistent with derivation from the Takaka Terrane. A rhyolite clast from the Pupu Conglomerate in northwest Nelson also has chemistry consistent with derivation from a Takaka Terrane source. We therefore correlate both volcanic clasts to the S-type Ridge Suite. No comparable S-type plutonic source of the same age has been recognised in the northwest Nelson section of the Takaka Terrane. These volcanic clasts represent the oldest recognised episode of S-type Ridge Suite magmatism in the Takaka Terrane.