Cratonisation of Archaean continental crust:Insights from U–Pb zircon geochronology and geochemistry of granitic rocks in the Narryer Terrane, northwest Yilgarn Craton

Assembly of the Yilgarn Craton in Western Australia was related to Neoarchaean magmatic episodes that stabilised an Archaean continent. Neoarchaean granitic magmatism across the Yilgarn Craton was typified by early (2750–2680 Ma) tonalite and granodiorite emplacement, followed by craton-wide 2680–2620 Ma granodiorite and monzogranite emplacement. Products of the younger magmatic event are the most voluminous in the Yilgarn Craton, although magma source compositions and tectonic settings related to magmatism have remained ambiguous. We report U–Pb zircon ages and whole-rock geochemistry of ultramafic, mafic, intermediate, and felsic magmatic rocks from the Narryer Terrane and the adjacent Youanmi Terrane in the northwestern Yilgarn Craton. Our results show that Neoarchaean magmatism occurred in three stages, at c. 2740 Ma, 2680 Ma, and 2630 Ma. The compositions of granitic magmas evolved during each stage, from relatively high CaO/K2O, V, and EuN/Eu* tonalite, granodiorite, and monzogranite to high K2O/Na2O, Zr, and Ga/Al2O3 monzogranite with A-type affinity. We infer that cratonisation of the northwestern Yilgarn Craton involved a change from convergent to intraplate tectonic environments during these three magmatic episodes. We suggest that thickening of Archaean continental nuclei through convergent tectonics was followed by extension and decompression melting of the lithosphere. The latter events triggered craton-wide crustal anatexis and episodic granitic magmatism, culminating in stabilisation of the Yilgarn Craton. This distinctive Neoarchaean crustal evolution, from convergent to intraplate regimes, appears to be consistent with late magmatism associated with cratonisation of other Archaean terranes, and reflects a unique process stabilising continental crust on the early Earth.
Assembly of the Yilgarn Craton in Western Australia was related to Neoarchaean magmatic episodes that stabilised an Archaean continent. Neoarchaean granitic magmatism across the Yilgarn Craton was typified by early (2750–2680 Ma) tonalite and granodiorite emplacement, followed by craton-wide 2680–2620 Ma granodiorite and monzogranite emplacement. Products of the younger magmatic event are the most voluminous in the Yilgarn Craton, although magma source compositions and tectonic settings related to magmatism have remained ambiguous. We report U–Pb zircon ages and whole-rock geochemistry of ultramafic, mafic, intermediate, and felsic magmatic rocks from the Narryer Terrane and the adjacent Youanmi Terrane in the northwestern Yilgarn Craton. Our results show that Neoarchaean magmatism occurred in three stages, at c. 2740 Ma, 2680 Ma, and 2630 Ma. The compositions of granitic magmas evolved during each stage, from relatively high CaO/K2O, V, and EuN/Eu* tonalite, granodiorite, and monzogranite to high K2O/Na2O, Zr, and Ga/Al2O3 monzogranite with A-type affinity. We infer that cratonisation of the northwestern Yilgarn Craton involved a change from convergent to intraplate tectonic environments during these three magmatic episodes. We suggest that thickening of Archaean continental nuclei through convergent tectonics was followed by extension and decompression melting of the lithosphere. The latter events triggered craton-wide crustal anatexis and episodic granitic magmatism, culminating in stabilisation of the Yilgarn Craton. This distinctive Neoarchaean crustal evolution, from convergent to intraplate regimes, appears to be consistent with late magmatism associated with cratonisation of other Archaean terranes, and reflects a unique process stabilising continental crust on the early Earth.