U–Pb zircon, zircon Hf and whole-rock Sm–Nd isotopic constraints on the evolution of Paleoproterozoic rocks in the northern Gawler Craton

Abstract

U–Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775–1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730–1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780–1750 Ma zircons are somewhat evolved with initial ε_Hf values –4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm–Nd values from most samples have relatively evolved initial ε_Nd values of –3.7 to –1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial ε_Hf zircon values of ca +5.2 to +8.2, and initial ε_Nd values of ∼+3.5 to +3.8. The presence of 1775–1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780–1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic.

Key Words:

• Gawler Craton
• Paleoproterozoic
• Hf isotope
• Nd isotope
• orthogneiss
• zircon

Acknowledgements

We would like to acknowledge Sam Deed for assistance with data collection. We are grateful to Benjamin Wade and Angus Netting of Adelaide Microscopy for invaluable assistance with the LA-ICPMS facility. David Bruce is thanked for assistance with Sm–Nd isotope analysis. We would also like to thank Norman Pearson from GEMOC for assistance with Lu–Hf isotopic analysis. Russell Korsch and William Griffin are thanked for thorough and constructive reviews, which greatly improved the manuscript. This work was supported by Australian Research Council Grant LP0454301 and Australian Research Council Discovery Project DP1095456, Collins, Hand & Condie, ‘The enigmatic link between crustal growth and supercontinent formation.’ The analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS, industry partners and Macquarie University. This contribution forms TRAX record number 165. This is contribution 754 from the Australian Research Council National Key Centre for the Geochemical Evolution and Metallogeny of Continents (URL: <http://www.gemoc. mq.edu.au>).