Cambrian ocean floor crust preserved in the Takaka Terrane, New Zealand

ABSTRACT

Cambrian igneous rocks in the Takaka Terrane of New Zealand provide important constraints for geodynamic reconstructions of the Cambrian SE Gondwana margin. We provide field data and a comprehensive trace element and isotope dataset for such rocks from the upper Baton River area in northwest Nelson, New Zealand, including the first combined Hf-Nd isotope data for Takaka Terrane rocks. These submarine volcanic rocks, known as Mataki and Benson volcanics of the Devil River Volcanics Group, are both interbedded with Haupiri Group sediments, providing a previously not observed direct stratigraphic link between the two volcanic units. Incompatible element abundances of Mataki Volcanics display a full spectrum from subduction-modified back-arc-tholeiites to E-MORB type tholeiites. Initial Hf-Nd isotope compositions are coupled, spanning a range from MORB-like to OIB-like compositions. The MORB-like endmember (initial ϵNd +7 and ϵHf +13), taps moderately depleted asthenospheric mantle. If extrapolated to present-day composition, this depleted mantle endmember does not resemble modern Pacific-type mantle, suggesting formation in a back-arc basin separated from Pacific mantle by a continent-ward, intra-oceanic subduction zone. The enriched asthenospheric mantle endmember in the Mataki Volcanics may be an equivalent to the sources of Neoproterozic or middle Cambrian intra-continental flood basalts in central and SE-Australia.

KEYWORDS:

• Takaka Terrane
• New Zealand
• mataki volcanics
• isotopes
• trace elements
• southeast Gondwana
• Baton river

Acknowledgements

This work builds on thesis work of all three authors in the 1990s where we started our scientific careers focusing on the geology of northwest Nelson in New Zealand. We are indebted to Roger Cooper for having introduced us into the Early Paleozoic geology of New Zealand with great commitment, patience and endurance. His holistic view on geology is highly appreciated. The Takaka Terrane still carries exciting geodynamic secrets that are a pleasure to unlock and made it a worthwhile endeavour to return to our scientific roots. We thank Alfred Schneider (formerly University of Göttingen, Germany, deceased) for constant support of our work in New Zealand. We also thank Josua Pakulla, Mike Jansen and Laurids Biermanski from Cologne for help during the ICPMS trace element measurements. Reviews by Tod Waight and John Foden as well as careful editorial comments by Richard Jongens helped to improve the paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data are included in the text as tables.