Structural evolution of a 1.6 Ga orogeny related to the final assembly of the supercontinent Nuna: coupling of episodic and progressive deformation

Volante, Dr Silvia1,2, Collins, Prof William J.1, Pourteau, Dr Amaury1, Li,Prof Zheng-Xiang1, Li, Jiangyu1, Nordsvan, Dr Adam1,3

1Earth Dynamics Research Group, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and The Institute for Geoscience Research (TIGeR), School of Earth and Planetary Sciences, Curtin University, Perth, Australia, 2Institute of Geology, Mineralogy and Geophysics, Ruhr-Universität Bochum, Bochum, Germany 3Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong

The poly-deformed Georgetown Inlier (GTI) in NE Australia has recently been suggested to record a 1.60 Ga orogenic event related to final Nuna assembly. However, the structural evolution of the inlier has remained poorly constrained at the regional-scale, and major tectono-thermal events occurred at c. 1.55 Ga. The GTI is the type-region for conceptualisation of crenulation cleavage development and where the foliation intersection axes (FIAs) approach has been applied. We re-evaluated both concepts by combining a multiscale petrostructural analysis with recent petrological and geochronological data. Three main deformation events (D1, D2, D3) and associated composite fabrics (S1, S2, S3) are identified in the GTI. The original NE-orientation of 1.60 Ga D1 compressional structures is preserved in the low-grade western domain, and the associated composite S1 fabric is retained as microstructural relicts within c. 1.55 Ga D2 low-strain domains to the east. Extensional D2 structures, characterised by a pervasive, high-grade, composite S2 foliation throughout the central and eastern domains, are interpreted as the footwall of a regional N-S-trending, W-dipping crustal-scale detachment zone. Syn-D2 S-type granites formed at 1.55 Ga as the detachment evolved. D1 stage was associated with Nuna assembly, whereas D2 represents post-collisional extension. Progressive foliation development occurred twice in the GTI, at 1.60 Ga (D1) and 1.55 Ga (D2), but the previous FIA analysis only records the 1.60 Ga event and cannot be easily reconciled with the regional structural analysis. This study highlights that a multiscale and multi-disciplinary approach is required to unravel the structural history of orogenic belts.


Our interest lies in reconstructing the structural, magmatic and metamorphic history of Proterozoic inliers to unravel the evolution of NE Australia during the Mesoproterozoic final assembly of the supercontinent Nuna by applying a multi-disciplinary and multi-scale approach which combines structural analysis with geochronology, metamorphic and igneous petrology and geochemistry.

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