Sediment provenance in the Murchison and Maruia basins, Aotearoa/New Zealand: a record of Neogene strike-slip displacement, convergence, and basement exhumation along the Australian–Pacific plate boundary

ABSTRACT

The Murchison and Maruia basins are situated on the Australian Plate adjacent the Alpine Fault, an ideal place to study Cenozoic Australian–Pacific plate boundary evolution. Sandstone provenance was investigated using petrographic and detrital zircon U–Pb geochronologic methods and primarily varies geographically. Secondary up-section variation tracks spatiotemporal changes in basement exhumation. Eocene–middle Miocene western Murchison Basin sandstone is arkosic, derived locally from Devonian–mid-Cretaceous granitoids. Early Miocene–?Pliocene eastern Murchison and Maruia basin sandstone is lithic-/plagioclase-rich, reflecting a mixed provenance: proximal Carboniferous–mid-Cretaceous granitoids, and distal mid-Cretaceous Median Batholith and Permian–Triassic Eastern Province metasedimentary sources in the Pacific Plate. This confirms early Miocene Pacific Plate exhumation during initial Alpine Fault evolution began in northern Fiordland/western Otago but the contrast between eastern and western Murchison Basin indicates limited westward sediment dispersal. Higher proportions of Brook Street Terrane (BST) detrital zircon in middle Miocene eastern Murchison Basin sandstone suggests accelerated Pacific Plate exhumation at c. 15 Ma. By c. 10 Ma, the eastern Murchison Basin BST source had switched to the Australian Plate due to Waimea–Flaxmore fault reverse reactivation and dextral plate boundary strike-slip displacement, which by the late Miocene/Pliocene led to Rakaia Terrane-affinity Haast Schist replacing Caples Terrane as the main Maruia Basin sediment source.

KEYWORDS:

• Murchison Basin
• Maruia Basin
• New Zealand
• provenance
• detrital zircon U–Pb geochronology
• point-count
• Alpine Fault
• Australian–Pacific plate boundary

Acknowledgements

David Flynn (VUW) and Malcolm Reid (OU) provided invaluable technical assistance with zircon CL imaging and U–Th–Pb–TE analyses, respectively. Hugh Morgans and Nick Mortimer (GNS Science) kindly provided biostratigraphic and additional petrographic analyses. The assistance of Jared Gooley and Nora Nieminski (USGS), and Henry Gard (GNS Science) with fieldwork is gratefully acknowledged. This study would not have been possible without the field mapping of the late Pat Suggate (GNS Science). Nick Mortimer (GNS Science) is thanked for reviewing an earlier version. Local landowners and the Department of Conservation (permit 40260-GEO) are thanked for permission to sample their properties and conservation estate, respectively. Thorough and helpful reviews by Jared Gooley and Kathleen Marsaglia (CSUN) lead to significant improvements to the manuscript.

Disclosure statement

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

Data availability statement

The sandstone point-count and detrital zircon U–Pb geochronologic data on which the findings of this study are based are accessible via the Open Science Framework at https://osf.io/vwt4m/?view_only = b3709bb0150446c6900b17f63ae7ca13 and are also freely available from the PETLAB database (https://pet.gns.cri.nz/), where they can be found by searching for one or more sample collection numbers (e.g. P91825) using either the Simple Query or Query Builder tools.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was part of the GNS Science Understanding Zealandia/Te Riu-a-Māui research programme, funded by the Ministry of Business, Innovation and Employment (MBIE) through the Strategic Science Investment Fund (SSIF).