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Archaean Cratonization and Deformation in the Northern Superior Province, Canada: an Evaluation of Plate Tectonic Versus Vertical Tectonic Models Jean H

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Archaean Cratonization and Deformation in the Northern Superior Province, Canada: an Evaluation of Plate Tectonic Versus Vertical Tectonic Models Jean H Precambrian Research 127 (2003) 61–87 Archaean cratonization and deformation in the northern Superior Province, Canada: an evaluation of plate tectonic versus vertical tectonic models Jean H. Bédard a,∗, Pierre Brouillette a, Louis Madore b, Alain Berclaz c a Geological Survey of Canada, Division Québec, 880, ch.Ste-Foy, Quebec City, Que., Canada G1S 2L2 b Géologie Québec, Ministère des ressources naturelles du Québec, 5700, 4e Avenue Ouest, Charlesbourg, Que., Canada G1H 6R1 c Géologie Québec, Ministère des ressources naturelles du Québec, 545 Crémazie Est, bureau 1110, Montreal, Que., Canada H2M 2V1 Accepted 10 April 2003 Abstract The Archaean Minto Block, northeastern Superior Province, is dominated by tonalite–trondhjemite, enderbite (pyroxene tonalite), granodiorite and granite, with subordinate mafic rocks and supracrustal belts. The plutons have been interpreted as the batholithic roots of Andean-type plate margins and intra-oceanic arcs. Existing horizontal-tectonic models propose that penetrative recrystallization and transposition of older fabrics during terrane assembly at ∼2.77 and ∼2.69 Ga produced a N-NW tectonic grain. In the Douglas Harbour domain (northeastern Minto Block), tonalite and trondhjemite dominate the Faribault–Thury complex (2.87–2.73 Ga), and enderbite constitutes 50–100 km-scale ovoid massifs (Troie and Qimussinguat complexes, 2.74–2.73 Ga). Magmatic muscovite and epidote in tonalite–trondhjemite have corroded edges against quartz + plagioclase, suggesting resorption during ascent of crystal-charged magma. Foliation maps and air photo interpretation show the common development of 2–10 km-scale ovoid structures throughout the Douglas Harbour domain. Outcrop and thin-section scale structures imply that many plutons experienced a phase of syn-magmatic deformation, typically followed by high temperature sub-magmatic overprints. Thermobarometric data for plutons indicate near-solidus recrystallization at 4–6 kbar pressures. The common preservation of syn-magmatic fabrics in plutons of different ages seems incompatible with the origin of these fabrics through superimposed regional orogenesis. The broad uniformity of intrusion ages and lithologies throughout the Minto Block, and the rarity of shallowly-dipping planar fabrics, also seem inconsistent with accretion of disparate older terranes, each of which should preserve distinct histories. A possible alternative explanation for these features is provided by vertical tectonic models, whereby buoyant felsic magmas ascended as crystal slurries, while dense supracrustal rocks (and solidified felsic intrusions emplaced into them) subsided as cold fingers (10–20 km-scale instabilities). Shear between upwelling and downwelling limbs would have concentrated in the weak intrusions, generating steeply-plunging syn-magmatic fabrics, and producing ductile overprints in solidified rocks. © 2003 Elsevier B.V. All rights reserved. Keywords: Archaean; Orogeny; Vertical tectonics; Minto Block; Superior Province; Cratonization ∗ Corresponding author. Tel.: +1-418-654-2671; fax: +1-418-654-2615. E-mail addresses: [email protected] (J.H. Bedard),´ [email protected] (L. Madore), [email protected] (A. Berclaz). 0301-9268/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0301-9268(03)00181-5 62 J.H. B´edard et al. / Precambrian Research 127 (2003) 61–87 1. Introduction and regional framework Skulski, 2000; Percival et al., 2001), which were inter- preted to represent cratonic nuclei. Juvenile isotopic Most recent Archaean crustal growth models in- signatures of Qalluviartuuq belt lavas (2.84–2.83 Ga) voke a near-uniformitarian process of subduction, were considered evidence for an intra-oceanic arc arc maturation, and lateral accretion of oceanic arcs setting (Skulski et al., 1996). A 2.81 Ga shear zone and plateaux (e.g. Condie, 1986; Card, 1990; de Wit, in the Qalluviartuuq belt was interpreted as an 1998; Percival et al., 2001). However, recent work intra-oceanic accretionary thrust (D1: Percival and in a number of cratons has favored vertical tectonic Skulski, 2000). However, analogous D1 structures models (e.g. Chardon et al., 1996; Collins et al., are younger in the Vizien belt (<2.718 Ga), and so 1998), leading to a revival of this classic debate. The D1 structures cannot record a unique tectonic event Minto Block (Fig. 1) is the largest plutonic-dominated (Percival and Skulski, 2000). Percival et al. (2001) terrane of the Superior Craton, and is an ideal proposed that a composite cratonic basement was place to investigate how Archaean crust formed and formed when oceanic and continental terranes docked stabilized. at about 2.77 Ga (Fig. 2), with crustally contaminated The Minto Block was poorly known prior to pio- neering work by Percival et al. (1992, 1994, 2001), who subdivided it into lithotectonic domains (Fig. 1), and developed tectonic models. The oldest Minto Block rocks are mafic and ultramafic lavas and felsic tuffs (3.825 Ga) from the Porpoise Cove greenstone belt, embedded in younger (2.75 Ga) tonalitic rocks of the Inukjuak domain (David et al., 2002). The next oldest Minto Block rocks are tonalite and trond- hjemite with embedded supracrustal belts from the Goudalie and Douglas Harbour domains (3–2.8 Ga: Stern et al., 1994; Madore et al., 1999; Percival and Fig. 1. Simplified map of Minto Block adapted from Percival Fig. 2. Cartoon illustrating existing plate-tectonic scenarios et al. (1997).PN= Pelican´ Nantais belt, Ko = Kogaluc belt, (Percival et al., 2001) for origin and assembly of Minto Block Vz = Vizien belt. domains. J.H. B´edard et al. / Precambrian Research 127 (2003) 61–87 63 calc-alkaline volcanics in the Kogaluc belt, Lac Minto Minto Block (D2) is interpreted as a 2.69 Ga over- domain, representing development of a successor print by Percival and Skulski (2000), then how is arc at 2.77–2.76 Ga (Skulski et al., 1996). Younger the pre-Leaf River suite accretion event (∼2.77 Ga) (<2.748 Ga), unconformable greywacke and iron for- manifested in terms of fabric development and meta- mations that contain ancient detritus (Percival et al., morphism, and what was the impact of the 2.69 Ga 1995), and quartzites and ultramafic lavas in the Farib- event on the older fabrics? ault belt (Douglas Harbour domain), were interpreted To clarify these issues, we present field, structural, as a continental overlap sequence (Percival et al., and petrographic data from the poorly-known north- 1997), linked to intra-arc extension by Skulski et al. eastern part of the Minto Block, recently mapped on (1994). a 1:250,000 scale (Figs. 3 and 4) by the Ministère This older composite basement was intruded by des Ressources Naturelles du Québec. After com- voluminous granodiorite and granite (subordinate paring our data with observations from elsewhere in tonalite, enderbite, pyroxene tonalite and mafic intru- the Minto Block, we discuss the relative merits of sions) of the Leaf River suite (2.73–2.72 Ga: Percival different tectonic models to explain the characteristic et al., 1994; Stern et al., 1994), which constitutes fabrics and lithological assemblages associated with most of the Lac Minto and Utsalik domains. Relict Archaean cratonization in this area. zircon cores and Nd-isotopic signatures indicate recy- cling of older continental crust, and so the Leaf River suite was interpreted to be the plutonic root zones 2. Douglas Harbour domain of Andean-type continental arcs (Stern et al., 1994; Percival et al., 1994). The great areal extent of syn- We divide the Douglas Harbour domain into the chronous magmatism and heterogeneous Nd-isotopic Faribault–Thury, Troie and Qimussinguat plutonic signatures were explained in terms of two simultane- complexes (FTC, TC and QC) (Figs. 3–5), each of ously active subduction zones (Fig. 2; Percival et al., which contains supracrustal belts. In the west, the FTC 2001). is cut by granodiorite, granite, pyroxene tonalite and Lin et al. (1996) originally proposed that collision enderbite of the Lepelle complex (2.729–2.727 Ga), and amalgamation of the Lake Minto, Goudalie and which envelops screens and enclaves of rocks equiv- Utsalik arcs generated the dominant N-NW foliation of alent to the FTC (Fig. 3, Kapijuq and Bottequin a regionally distributed, tectono-metamorphic episode suites). To the northeast, Diana complex gneisses (D2). Subsequently, Percival and Skulski (2000) dated (2.78–2.76 Ga) were juxtaposed against the Douglas a D2 fabric at 2.693–2.675 Ga and re-interpreted Harbour rocks during Proterozoic dextral compres- D2 as an overprint related to overthrusting of the sion (Madore and Larbi, 2000), which overprints the 2.71–2.70 Ga Tikkerutuk continental arc onto the eastern FTC (Figs. 1, 3 and 5). To the south, Troie amalgamated Lac Minto + Goudalie + Utsalik + complex rocks are intruded by Utsalik domain granite Douglas Harbour proto-craton (Fig. 2, at 2.7 Ga). and granodiorite (Berclaz et al., 2001; Leclair et al., They further proposed that deformation and amphibo- 2001a). lite to granulite facies metamorphism in supracrustal The FTC is dominated by hornblende tonalite and belts of the west-central Minto Block resulted from biotite trondhjemite (Fig. 6a), with subordinate dior- this crustal thickening event, with transposition and ite, granodiorite and granite. Western FTC tonalites recrystallization of older fabrics into the dominant yield 2.88–2.86 Ga crystallization ages, while eastern N-NW grain, and production of crustally-derived plu- FTC tonalites yield younger ages between 2.81 and tons and diatexites (2.69 Ga). Subsequent activity is 2.77 (Madore et al., 1999; Madore and Larbi, 2000; manifested as a series of less penetrative deformation Percival et al., 2001). Inherited zircon cores yield ages events (D3–D5: Lin et al., 1996; Percival and Skulski, up to 3 Ga (Percival et al., 2001), indicating recy- 2000) and late- to post-tectonic granitoid and syen- cling of older sialic material. The age of FTC pluton- ite intrusions (2.696–2.645 Ga: Stern et al., 1994; ism overlaps with ages from embedded supracrustal Skulski et al., 1996; Percival and Skulski, 2000).
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