Age and structure of the Permian Brook Street Terrane, Takitimu Mountains, New Zealand

ABSTRACT

We use a recently completed airborne magnetic and gamma-ray spectrometric survey, and new U/Pb and ⁴⁰Ar/³⁹Ar age determinations, to revise and clarify several aspects of Brook Street Terrane geology in the Takitimu Mountains. Steeply dipping and homoclinal Permian Takitimu Subgroup formations defined in the central part of the range can, with moderate confidence, be traced along strike to other parts of the range where they are more complexly folded and faulted. We report intrusion ages for three Brook Street plutonic suites: pyroxene-bearing White Hill Intrusives (306-270 Ma, U/Pb zircon), amphibole-bearing Mackinnon Peak Intrusives (261 ± 1 Ma, ⁴⁰Ar/³⁹Ar amphibole), and shoshonitic Wether Hill Dikes (254 ± 1 Ma, ⁴⁰Ar/³⁹Ar plagioclase). Geological relationships between these intrusions and the host Takitimu Subgroup reinforce the Early Permian age of the latter, which is distinct from the overlying Late Permian Productus Creek Group. The Wether Hill Dikes mark the cessation of igneous activity in the Brook Street Terrane at c. 254 Ma. A large (n = 499) dataset of detrital zircon U/Pb ages from the nonmarine Jurassic Barretts Formation confirms a local Median Batholith-Tuhua Intrusives provenance and supports a post-Permian fore-arc tectonic setting along the Gondwana margin.

KEYWORDS:

• New Zealand
• Eastern Province
• Brook Street Terrane
• Permian
• igneous rocks
• stratigraphy
• geochronology
• remote sensing
• tectonics

Acknowledgements

We thank Anneka Greve, Will Oliver, and High Country Helicopters of Orawia for assistance in the field, and Struan Minty of Beaumont Station and Ceri Lewis of Mount Linton Station for access. Karine Haroumi Moromizato is acknowledged for technical support and guidance. Various aspects of this work were discussed with Oliver Nebel, Richard Kellett and Donna Eberhart-Phillips. The manuscript was improved by comments from Rose Turnbull, Andy Tulloch and Carl Spandler.

Disclosure statement

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

Data availability statement

Supplemental Files 1–5 are available in the Figshare online repository at https://doi.org/10.6084/m9.figshare.20004392. Supplemental File 1 contains whole rock geochemical methods and analytical data. Supplemental File 2 describes U/Pb isotopic methods, and contains cathodoluminescence images and age distribution plots of zircons from sample 010-TK. Supplemental File 3 is a table of all U-Pb zircon analytical data. Supplemental File 4 is a catalogue of photomicrographs of samples dated by ⁴⁰Ar/³⁹Ar methods. Supplemental File 5 describes ⁴⁰Ar/³⁹Ar methods, and contains age plots and provisional interpretive comments for all aliquots dated by ⁴⁰Ar/³⁹Ar methods.

Additional information

Funding

Mortimer acknowledges the New Zealand Ministry of Business Innovation and Employment’s Strategic Science Investment Fund grant C05X1702 to GNS Science.