Structural Evolution of a 1.6 Ga Orogeny Related to the Final Assembly of the Supercontinent Nuna: Coupling of Episodic and Progressive Deformation

Abstract

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 circa 1.55 Ga. The GTI is the type region for conceptualization of crenulation cleavage development and where the foliation intersection axes (FIAs) approach has been applied. We reevaluated both concepts by combining a multiscale petrostructural analysis with recent petrological and geochronological data. Three main deformation events (D1-D3) and associated composite fabrics (S1-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 circa 1.55 Ga D2 low-strain domains to the east. Extensional D2 structures, characterized 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 postcollisional extension. Progressive foliation development occurred twice in the GTI, at 1.60 (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 multidisciplinary approach is required to unravel the structural history of orogenic belts.

Constraints on the Palaeoproterozoic tectono‐metamorphic evolution of the Lewisian Gneiss Complex, NW Scotland: Implications for Nuna assembly

“…Palaeogeographic reconstructions correlate the LGC to the Archean and Palaeoproterozoic evolution of the North Atlantic and Rae cratons prior to and during the amalgamation of the Earth's first supercontinent Nuna (Baba, 2002; Hughes et al, 2014; Park, 2022; Park & Tarney, 1987). Between 2000 Ma and 1600 Ma, major collisional orogenic belts formed across the globe as a result of convergence, accretion and collision between different major cratons and smaller crustal blocks to form the supercontinent Nuna (Figure 14; e.g., Kirscher et al, 2021; Nordsvan et al, 2022; Pourteau et al, 2018; Volante, Collins, et al, 2020; Volante, Pourteau, et al, 2020; Volante et al, 2022; Wan et al, 2020). Several active margins and convergence directions between adjacent cratonic blocks forming Laurentia and Baltica generated major Palaeoproterozoic (1900–1700 Ma) orogenic belts (Figure 14) such as the Nagssugtoqidian Orogen, following collision between the Rae and the North Atlantic cratons, and the Lapland‐Kola Orogen after the collision between the Karelia and the Kola cratons (Buchan et al, 2000; St‐Onge et al, 2009).…”

“…In this study, petrographic and structural (i.e., petrostructural after Volante, Collins, et al, 2020) investigations were carried out on felsic and mafic lithologies across the central (Figure 3), northern (Figure 4) and southern (Figure 5) regions (Table 1) to better constrain the Laxfordian tectono‐metamorphic evolution of the mainland LGC. Three felsic gneisses (samples LC1903, LC1803 and LC1930) were collected from high‐strain zones within the central region where Badcallian fabrics (Figure 6a,b) are pervasively reworked by Inverian and/or Laxfordian deformation (Figure 3).…”

“…The high‐strain and complex nature of this D1 pervasive gneissic foliation is evidenced by parallel, stretched, thinned and boudinaged abundant mafic lenses and pods as well as subparallel, stretched and/or boudinaged syn‐ to late‐kinematic leucocratic veins (Figure 6a). Considering that the pre/early D1 foliation and S1 both developed during syn‐kinematic and continuous melt segregation (Johnson & White, 2011; Zirkler et al, 2012; e.g., Feisel et al, 2018), the folded, differentiated fabric could be either related to an earlier deformation event or, more likely, reflects early stages of the D1 event (early‐S1) during which progressive folding and fabric development occurred under high‐temperature conditions (e.g., Volante, Collins, et al, 2020). Therefore, the simple nature of the ‘Badcallian’ layering may obscure a complex and progressive deformation history that is commonly homogenized and obliterated under granulite facies conditions.…”

Mineralization proximal to the final Nuna suture in northeastern Australia

“…From ca. 1600-1550 Ma, the Etheridge Group was polydeformed and metamorphosed during the Jana Orogeny (Boger and Hansen, 2004;Cihan et al, 2006;Pourteau et al, 2018;Volante et al, 2020b;Volante et al, In Press;Withnall et al, 2013).…”

Heterogeneous Exhumation of the Mount Isa Orogen in NE Australia After 1.6 Ga Nuna Assembly: New High‐Precision40Ar/39Ar Thermochronological Constraints

“…Despite the period of global orogenesis between circa 2.10 and 1.80 Ga, the supercontinent Nuna (also known as Columbia; Evans & Mitchell, 2011; Evans et al, 2016; Rogers & Santosh, 2002; Zhang et al, 2012; Zhao et al, 2002) was not completely assembled until the juxtaposition between Australia with Laurentia (North America) at circa 1.60 Ga (Figure 1a) (Betts et al, 2016; Kirscher et al, 2019, 2020; Nordsvan, Collins, Li, Spencer, et al, 2018; Pehrsson et al, 2016; Pisarevsky et al, 2014). In western Laurentia, this final Nuna amalgamation event was recorded by the Racklan and Forward orogenies (Furlanetto et al, 2013; Thorkelson et al, 2005), whereas in northeast Australia coeval orogenesis was recorded by the Isan and Jana orogenies of the Mount Isa and Georgetown inliers (Figure 1b), respectively (Betts et al, 2008; Pourteau et al, 2018; Volante, Collins, et al, 2020; Volante, Pourteau, et al, 2020; Withnall & Hutton, 2013).…”