Northern QLD rocks provide insight into some of Australia's most significant mineral provinces

Work undertaken by EDRG researchers has examined the history of the crust in northern Queensland following the assembly of the supercontinent Nuna (approx. 1.6 billion years ago) and provides insight into the genesis of the Mt Isa and Broken Hill mineral provinces.

The study, published in the Geological Society of America Bulletin, examined the crustal evolution of a select northern QLD region over the ~100 million years following the assembly of Nuna. Using high-precision ⁴⁰Ar/³⁹Ar thermochronology, the cooling history of the Georgetown Inlier, which consists of 3 distinct domains separated by tectonic faults and metamorphic charateristics, could be used to decipher the timing, kinematics and magnitudes of the fault movements following the collision of Laurentia an NE Australia 1.6 billion years ago. This data, along with previously published data constraining the structure, geochronology, and petrography of the region enabled the researchers to interpret the broader tectonic significance.

Simplified lithological map of the Georgetown Inlier in northern Queensland, Australia showing the successive stratigraphic packages and the main fault zones.

It was found that differential exhumation histories of the domains that constitute the Georgetown Inlier, along with those from other nearby domains, could be explained through a coherent tectonic model. The model suggests extensional activation of lithospheric faults associated with orogenic collapse and delamination, with the associated magmatism representing melts caused by decompression, heat from the upwelling hot asthenosphere, and perhaps fluids released from the delaminated orogenic root.

The protracted orogenic history in the Georgetown–Mt Isa region, a lack of evidence for high pressure metamorphism, and the width of the orogen, can best be explained by a “soft-collision” during the final assembly of the supercontinent Nuna in a warmer Earth during the Paleoproterozoic.

This model and interpretation have wider implications into the mineralisation of the worlds largest zinc-lead ore deposit at Broken Hill, which was also proximal to Laurentia during the assembly of Nuna.

Conceptional model for the tectonic evolution of NE Australia from 1.60 Ga to 1.50 Ga. (A) The ca. 1.60 Ga continental collision event recorded westward accretion of the Georgetown Inlier in northern Queensland, Australia with synchronous orogenesis and crustal shortening recorded in both the Mount Isa and Georgetown inliers. (B) The orogenic root started to delaminate at ca. 1.55 Ga, replaced by upwelling asthenosphere mainly in the Georgetown Inlier and partially in the Mount Isa Inlier. Elevated geotherm by hot mantle upwelling, together with water released from the sunken crust and reduced pressure caused by orogenic collapse, induced widespread post-kinematic magmatism and exhumation in the Georgetown Inlier, but also some melting in the Mount Isa Inlier. (C) Complete detachment of the lower lithosphere from the Isa region started the younger magmatism, extension, and exhumation in the Mount Isa Inlier (Li et al., 2020) and continued extension and exhumation in the Georgetown Inlier (this study). V—vertical to horizontal ratio (= 1.3).

Contact person: Prof. Zheng-Xiang Li, Earth Dynamics Research Group, Curtin University.

Relevant publication:

Li, J., Li, Z.X., Pourteau, A., Jourdan, F., Volante, S., Nordsvan, A.R., Collins, W.J., Olierook, H.K.H., 2026. Crustal exhumation in the Georgetown Inlier of NE Australia after 1.6 Ga Nuna assembly: New insights from Ar thermochronology. Geological Society of America Bulletin. https://doi.org/10.1130/B38303.1