Pb, Nd, and Sr Isotopes and REE Systematics of Cambrian Sediments from New Zealand: Implications for the Reconstruction of the Early Paleozoic Gondwana Margin along Australia and Antarctica

Abstract

The Takaka Terrane of New Zealand’s South Island contains a Middle to early Late Cambrian intraoceanic island arc assemblage that consists of the terrigeneous to volcanogenic Haupiri Group sediments and the predominantly mafic Devil River Volcanics. Pb, Nd, and Sr isotopes, and major and trace element data are presented here for the Haupiri Group sediments. These data have implications for (1) the stratigraphy of the Takaka Terrane, (2) the reconstruction of the Cambrian Gondwana margin along Australia/Antarctica, and (3) geochemical and isotope provenance studies in general. Nd isotopes, Th/Sc, and rare earth elements (REE) show that the volcaniclastic components in the Haupiri Group sediments reflect the concomitant island arc and back‐arc volcanism. These sediments can probably be linked with the Early Cambrian Kanmantoo Group and Ordovician Lachlan Fold Belt sediments in SE Australia. To explain the Nd isotope compositions, published detrital zircon populations, and paleocurrent data, an Antarctic source with Grenvillian and Ross‐Delamerian age granitoids, as well as a significant portion of reprocessed Paleoproterozoic and/or Archean crust, is required. We adopt a bipolar subduction model for the Cambrian Gondwana margin along Australia/Antarctica and support the previous suggestion that the Cambrian arc assemblages of the Takaka Terrane of New Zealand and the Antarctic Bowers Terrane belong to the same arc system with a paleogeographical position offshore the Antarctic continent.