Tectonic switching within a long-lived convergent margin: evidence from the geochemistry of Paleoproterozoic granitoids, Dajarra region, Mount Isa Inlier

Paleoproterozoic granitoids of the Mount Isa Inlier record a prolonged history of crustal magmatism linked to the tectonic evolution of the North Australian Craton during assembly of the Nuna supercontinent. This study presents a lithogeochemical investigation of intrusions from the Dajarra region, in the southern Western Fold Belt, to constrain their geochemical characteristics, petrogenesis, and tectonic setting. The intrusions were emplaced at ca 1850–1650 Ma and correspond to four major magmatic episodes: the Kalkadoon, Argylla, Wonga-Burstall and Sybella igneous events. Thirty-three representative samples of plutons and associated dykes were analysed for whole-rock major and trace elements. The granitoids are dominantly felsic (SiO2, 62.6–76.7 wt%), with low MgO and TiO2 contents, high total alkalis and coherent fractionation trends consistent with extreme magmatic differentiation. Most samples are ferroan, alkalic-calcic to calc-alkalic and strongly peraluminous, whereas the Kalkadoon (KIE) sample is metaluminous. Trace-element patterns are characterised by enrichment in large ion lithophile elements and high-field-strength elements (HFSEs), pronounced negative Nb, Ti, Sr and Eu anomalies, and moderately to strongly fractionated rare earth element patterns. Distinct geochemical differences are observed between granitoid suites and across major structural boundaries, notably between Argylla intrusions east (AIE-E) and west (AIE-W) of the Rufus Fault. Many AIE-E, Wonga-Burstall and Sybella samples display elevated HFSE abundances and high zircon saturation temperatures, whereas AIE-W samples are HFSE-poor and exhibit lower temperatures, consistent with S-type affinities. On granite discrimination diagrams, most samples plot near the I- and A-type boundary and mainly within the A2 field, indicating derivation from reworked continental crust. This suggests that granitoid magmatism in the Dajarra region was dominated by partial melting of continental crust, with episodic mantle input required to achieve high melt temperatures. The magmatism occurred within a long-lived convergent margin system characterised by tectonic switching between contractional and extensional regimes during the Paleoproterozoic evolution of the Mount Isa Inlier.

Australian Journal of Earth Sciences

Australian Journal of Earth Sciences

N/A

1440-0952

N/A

N/A

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