Detrital zircon geochronology of the Speewah Group, Kimberley region, Western Australia: evidence for intracratonic development of the Paleoproterozoic Speewah Basin

ABSTRACT

Field observations integrated with new petrographic and sensitive high-resolution ion microprobe (SHRIMP) U–Pb age data for detrital zircons from the Paleoproterozoic Speewah Group of northern Western Australia provide evidence of depositional conditions, source of detritus, timing and evolution of the sedimentary rocks in the Speewah Basin. The Speewah Group is a 1.5 km-thick succession of poorly outcropping, predominantly siliciclastic rocks that preserve a fluviatile to marine, transgressive and regressive event. The Speewah Group unconformably overlies crystalline rocks of the Lamboo Province that were stabilised by the 1870–1850 Ma Hooper Orogeny, then accreted as the Kimberley region onto the North Australian Craton during the 1835–1810 Ma Halls Creek Orogeny. Unconformably overlying the Speewah Group is about 4 km of predominantly siliciclastic marine sedimentary rocks of the Kimberley Group in the Kimberley Basin. This study has detected a detrital zircon component within the Speewah Basin at 1814 ± 10 Ma, with a youngest zircon at 1803 ± 12 Ma (1σ) in fluviatile sandstones located beneath a volcaniclastic rock with magmatic zircons that have been dated at ca 1835 Ma. Previous studies proposed that the Speewah Basin developed as a retro-arc foreland basin during accretion of the North Australian Craton. We interpret the ca 1835 Ma zircons in the volcaniclastic rocks to be xenocrystic in origin. This new 20 million years younger maximum depositional age indicates that the Speewah Group in the Speewah Basin, similarly to the overlying Kimberley Group in the Kimberley Basin, developed in a post-orogenic setting on the North Australian Craton rather than in a syn-orogenic setting associated with the 1835–1810 Ma Halls Creek Orogeny.

KEYWORDS:

• Detrital zircon geochronology
• Kimberley region
• North Australian Craton
• Speewah Group

Acknowledgements

King River Copper Ltd (previously Niplats Australia Ltd) would like to thank the State Government of Western Australia for the grant from the Exploration Incentive Schemes, which contributed to the deep diamond drilling program on the study area and provided the samples for this study. U–Pb measurements were conducted using the SHRIMP II ion microprobes at the John de Laeter Centre at Curtin University in Perth, Australia. This work was carried out as part of foundation research project ‘Metal Sources and Transport Mechanisms in the Deep Lithosphere’ in the Australian Research Council (ARC) Centre of Excellence for Core to Crust Fluid Systems (CCFS). Marco Fiorentini acknowledges support through the ARC Centre of Excellence for Core to Crust Fluid Systems (CE11E0070) and support from the Australian Research Council through Linkage Project LP120100668 and the Future Fellowship Scheme (FT110100241). This is contribution 926 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au). We would like to acknowledge the very insightful reviews of Ian Tyler and Ian Fitzsimons, who have greatly improved the quality of the manuscript. The authors are also grateful for comments from David Maidment, and Christopher Phillips. MTDW publishes with permission of the Executive Director of the Geological Survey of Western Australia. The authors would like to thank the Directors of King River Copper for permission to publish the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Australian Research Council [grant no. CE11E0070].