Deformation in the Agnew-Wiluna Greenstone Belt and host Kalgoorlie Terrane during the c. 2675–2630 Ma Kalgoorlie Orogeny: ∼45 Ma of horizontal shortening in a Neoarchean back-arc region

Abstract

This study re-evaluates the tectonic processes that contributed to the final assembly of the Yilgarn Craton (Western Australia) in the late Neoarchean. We combine regional-scale (10–100 km) geological data collected from surface exposures over the Agnew-Wiluna Greenstone Belt (AWGB) in the Kalgoorlie Terrane of the Eastern Goldfields Superterrane (EGST) together with published and open-file geochronological and structural data from the Geological Survey of Western Australia. The combined datasets are then compared with the structural record in the Kalgoorlie Terrane, allowing for new insights into the tectonic evolution of the EGST and broader Yilgarn Craton. We show that c. 2675–2630 Ma orogenic deformation in the AWGB was associated with a protracted sequence of events, marked by the activation of distinct shear zones through time and repeated shifts in the location of sedimentary depocentres. We propose that the observed strain pattern resulted from the complex interplay of deformation, magmatism, and sediment deposition under progressive, ENE-WSW-directed horizontal shortening spanning ∼45 Ma. We suggest that the identified deformation scheme represents the local expression of tectono-thermal events affecting the Kalgoorlie-Kurnalpi Rift and broader EGST. Building on prior knowledge on the geological evolution of the Yilgarn Craton, our study supports a model proposed more than a decade ago whereby orogenesis was driven by a west-dipping, outboard subduction zone located further east of the exposed margins of the Yilgarn Craton. Lastly, we emphasize that such scale-integrated, unified perspective provides a balanced reconciliation between the debated allochthonous and para-autochthonous models for the EGST.