Post-convergent structures in lower parts of the 1090–1050 Ma (early-Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield

Schwerdtner, W. M.; Rivers, Toby; Zeeman, Brant; Wang, C.C.; Tsolas, Jason; Yang, Jack; Ahmed, Madeeha

doi:10.1139/cjes-2013-0108

Cited by 9 publications

(22 citation statements)

References 85 publications

(173 reference statements)

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“…In the exhumed mid crust, reliable estimates of the amount of extensional strain are probably not feasible from measurements of outcrop-scale structures, which may record only a finite increment of the total strain. Use of larger strain markers such as plutons, crustalscale boudins, and entire domains should help (Schwerdtner et al 2014), but the ultimate aim should be strain determinations using an external reference frame. Moreover, all such estimates need to be linked to the amount of extension in the orogenic superstructure.…”

Section: Some Future Research Directionsmentioning

confidence: 99%

Tectonic Setting and Evolution of the Grenville Orogen: An Assessment of Progress Over the Last 40 Years

Rivers

2015

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SUMMARYThe Grenville Province is known for its high grade of metamorphism, complex ductile gneissic structure, and polyphase reworking, features indicative of residence in the deep crust (orogenic infrastructure) that hamper recognition of protoliths and original relationships and render tectonic interpretations especially challenging. This paper charts the evolving understanding from the 'Grenville Problem' of the 1950s before the plate tectonic paradigm, through a speculative quasiplate tectonic stage in the 1970s that effectively proved to be a dead end, and the first constrained plate tectonic models for pre-Grenvillian Laurentia in the 1980s, to the recent LHO (large hot orogen) and collapsed LHO models for the Grenville Orogen itself. The collapsed LHO model is based on the finding that significant amounts of the superstructure (upper orogenic crust) are preserved, and that the present crustal architecture can be explained by tectonic juxtaposition of infrastructure and superstructure in a late extensional event associated with crustal-scale collapse of a high-strain channel under an orogenic plateau. Conceptual breakthroughs and critical datasets assembled in the period 1980-2000 that were influential in guiding tectonic thinking are discussed and it is argued that present understanding was contingent on the results of 2-D numerical forward modelling of orogenesis, in particular the LHO experiments and the more recent models of orogenic collapse. As a result, for the first time a conceptual plate tectonic model for the convergence and collapse stages of the Grenville Orogen based on empirical field data (the inverse model) is broadly supported by numerical forward-modelling experiments constrained by physically plausible processes in a LHOand both are available for future testing and refinement. Moreover, they may also have application to other enigmatic high-grade Proterozoic orogens that have resisted simple incorporation within the plate tectonic narrative.

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Section: Some Future Research Directionsmentioning

confidence: 99%

Tectonic Setting and Evolution of the Grenville Orogen: An Assessment of Progress Over the Last 40 Years

Rivers

2015

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“…Moreover, peak P-T estimates for the amphibolite-facies assemblages in the Muskoka domain are not distinctly different from those for the granulites, being in the range 1000-1100 MPa and 750-800°C, leading Timmermann et al (2002) to deduce that the distribution of granulite-and amphibolite-facies assemblages in the transition zone was a function of the a H2O in the ambient fluid. Timmermann et al (1997) dated a Hbl-Bt-bearing, foliation-parallel leucosome in amphibolite-facies gneiss in the Muskoka domain at 1064 ±18 Ma (U-Pb zircon, TIMS), a result subsequently confirmed more precisely by the SHRIMP method (1067 ±9 Ma;Slagstad et al 2004b), and Bussy et al (1995) presented U-Pb TIMS data for metamorphic zircon in dykes in the Moon River subdomain that bracketed the timing of amphibolite-facies ductile deformation between ca. 1065 and 1045 Ma.…”

Section: Ottawan Metamorphism In the Muskoka Domainmentioning

confidence: 80%

“…2) is used as a tectonic template in this study. In this figure, the SE-dipping allochthonous sheets in the hanging wall of the Allochthon Boundary (structural levels 2-3) were emplaced during the main Ottawan collisional phase of the Grenvillian Orogeny (~1090-1020 Ma), and overlie the parautochthon in its footwall (structural level 1) that underwent its principal deformation in the Rigolet phase (~1005-980 Ma;Rivers et al 2012). Specifically the southeast part of structural level 3 is composed of the Muskoka domain and its Moon River and Seguin subdomains that are correlated with the Ahmic and Shawanaga subdomains farther northwest, all of which overlie the Algonquin-Lac Dumoine domain and related subdomains of structural level 2.…”

Section: Metamorphic Core Complexesmentioning

confidence: 97%

“…These interpretations were given concrete expression by U-Pb zircon dating of extensional reworking of the Allochthon Boundary at ~1020 Ma by , and since then a range of evidence for post-peak extension has been described (e.g. Nadeau and van Breemen 1998;Carr et al 2000;Timmermann et al 2002;Rivers 2008Rivers , 2012Jamieson et al 2010;Schwerdtner et al 2014). However, as discussed below its extent remains poorly constrained.…”

Section: Metamorphic Core Complexesmentioning

confidence: 99%

“…However, more recently the data from both levels have been integrated with estimates of regional peak pressure variations during the Ottawan metamorphism, leading to a more holistic picture (Fig. 3;Rivers 2008;2012;Rivers et al 2012;McLelland et al 2013;Schwerdtner et al 2014). In this interpretation, parts of the orogenic superstructure, preserved segments of which are referred to as the orogenic lid, are juxtaposed against exhumed mid-crustal gneiss terranes such as the ORGC (orogenic infrastructure), implying that after crustal thickening and peak metamorphism the orogen underwent profound orogenic collapse (also known as gravitational collapse, extensional collapse, or gravitational spreading).…”

Section: The Large Hot Orogen (Lho) Paradigmmentioning

confidence: 99%

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Post-peak Evolution of the Muskoka Domain, Western Grenville Province: Ductile Detachment Zone in a Crustal-scale Metamorphic Core Complex

Rivers

Schwerdtner

2015

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The Ottawa River Gneiss Complex (ORGC) in the western Grenville Province of Ontario and Quebec is interpreted as the exhumed mid-crustal core of a large metamorphic core complex. This paper concerns the post-peak evolution of the Muskoka domain, the highest structural level in the southern ORGC that is largely composed of amphibolite-facies straight gneiss derived from retrogressed granulite-facies precursors. It is argued that retrogression and high strain occurred during orogenic collapse and that the Muskoka domain acted as the ductile detachment zone between two stronger crustal units, the underlying granulite-facies core known as the Algonquin domain and the overlying lower grade cover comprising the Composite Arc Belt. Formation of the metamorphic core complex followed Ottawan crustal thickening, peak metamorphism and possible channel flow, and took place in a regime of crustal thinning and gravitational collapse in which the cool brittle–ductile upper crust underwent megaboudinage and the underlying hot ductile mid crust flowed into the intervening megaboudin neck regions. Post-peak crustal thinning in the Muskoka domain began under suprasolidus conditions, was facilitated by widespread retrogression, and was heterogeneous, perhaps attaining ~90% locally. It was associated with a range of ductile, high-temperature extensional structures including multi-order boudinage and associated extensional bending folds, and a regional system of extension-dominated transtensional cross-folds. These ductile structures were followed by brittle–ductile fault propagation folding at higher crustal level after the gneiss complex was substantially exhumed and cooled. Collectively the data record ~60 m.y. of post-peak extension on the margin of an exceptionally large metamorphic core complex in which the ductile detachment zone has a true thickness of ~7 km. The large scale of the core complex is consistent with the deep level of erosion, and the long duration of extensional collapse is compatible with double thickness crust at the metamorphic peak, the presence of abundant leucosome in the mid crust and widespread fluid-fluxed retrogression, collectively pointing to the important role of core complexes in crustal cooling after the peak of the Grenvillian Orogeny.RÉSUMÉLe complexe gneissique de la rivière des Outaouais (ORGC) dans la portion ouest de la Province de Grenville au Québec et en Ontario est interprété comme le cœur d’un grand complexe métamorphique à coeur de noyau. Le présent article porte sur l’évolution post-pic du domaine de Muskoka, soit le niveau structural le plus élevé de l’ORGC composé en grande partie d’orthogneiss au faciès amphibolite dérivés de précurseurs au faciès granulite. Nous soutenons que la rétromorphose et les grandes déformations se sont produites durant l’effondrement orogénique et que le domaine de Muskoka en a été une zone de détachement ductile entre deux unités crustales plus résistantes, le cœur au faciès granulite sous-jacent étant le domaine Algonquin, et la chapeau sus-jacent à plus faible grade de métamorphisme comprenant le Ceinture d’Arc Composite. La formation du complexe métamorphique à coeur de noyau est survenue après l’épaississement crustale ottavien, le pic métamorphique et le possible flux en chenal, et s’est produit en régime d’amincissement crustal et d’effondrement gravitationnel au cours duquel la croûte supérieure refroidie a subit un mégaboudinage et où la croûte moyenne chaude et ductile sous-jacente a flué dans les régions entre les mégaboudins. L’amincissement crustale post-pic dans le domaine de Muskoka, qui a débuté en conditions suprasolidus, a été facilité par une rétromorphose généralisée, hétérogène, atteignant à peu près 90 % par endroits. Celle-ci a été associée avec une gamme de structures d’extension ductiles de haute température, incluant du boudinage de plusieurs ordres de grandeur et de plis de flexure d’extension, ainsi qu’un système régional de plis croisés d’origine transtensionnelle. À ces structures ductiles a succédé une phase de plissement de propagation de failles cassantes à ductiles à un plus haut niveau crustal, après que le complexe gneissique ait été exhumé et se soit refroidi. Prises ensemble, les données indiquent une extension post-pic sur la marge d’un complexe métamorphique à coeur de noyau exceptionnellement grand aux environs de 60 m.y. et dans laquelle la zone de détachement montre une épaisseur véritable d’environ 7 km. La grandeur de l’échelle du complexe métamorphique à coeur de noyau concorde avec le fort niveau d’érosion, et la grande durée de l’effondrement d’extension est compatible avec une croûte de double épaisseur au pic de métamorphisme, la présence de leucosomes abondants dans la croûte moyenne et d’une rétromorphose à flux fluidique généralisée, l’ensemble indiquant l’importance du rôle des complexes métamorphiques à coeur de noyau dans le refroidissement de la croûte après le pic de l’orogenèse grenvillienne.

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Tectono-metamorphic history of the eastern Taureau shear zone, Mauricie area, Québec: Implications for the exhumation of the mid-crust in the Grenville Province

Gervais

Tremblay²,

Crowley³

et al. 2015

Precambrian Research

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International audienceThis study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mékinac-Taureau domain of the Mauricie area, central Grenville Province. Macro- and micro-structural analyses reveal the top-down-to-the-ESE sense of shear on the eastern Taureau shear zone, a major extensional structure that exhumed the mid-crustal Mékinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mékinac-Taureau domain, inferred to be the result of northwestward thrusting and regional crustal thickening, took place under P–T conditions of 1000–1100 MPa and 820–880 °C prior to 1082 ± 20 Ma. Retrograde conditions varying from 775 to 675 °C and from 800 to 650 MPa were registered in its upper structural levels prior to and/or during shearing along the eastern Taureau shear zone that was active at 1064 ± 15 Ma. The Shawinigan domain records P–T conditions ranging from 850 to 625 MPa and from 775 to 700 °C, P–T values that are similar to or slightly lower than those for retrogressed samples from the upper structural levels of the Mékinac-Taureau domain, but clearly lower than the peak metamorphism values of the latter domain. Finally, the area cooled below 550–600 °C at ∼1000–1030 Ma and below 450 °C at ∼900–970 Ma on the basis of 40Ar/39Ar geochronology on amphibole and biotite. Structural and metamorphic characteristics of the Mauricie area are similar to those expected from a metamorphic core complex formed during post-convergence orogenic collapse in a gravity-driven fixed-boundary mode. The Mékinac-Taureau and Shawinigan domains were thus probably exhumed by a similar process, which supports the orogenic collapse model recently proposed to explain the exhumation of mid-crustal metamorphic core complexes in the Grenville Province

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Post-convergent structures in lower parts of the 1090–1050 Ma (early-Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield

Cited by 9 publications

References 85 publications

Tectonic Setting and Evolution of the Grenville Orogen: An Assessment of Progress Over the Last 40 Years

Tectonic Setting and Evolution of the Grenville Orogen: An Assessment of Progress Over the Last 40 Years

Post-peak Evolution of the Muskoka Domain, Western Grenville Province: Ductile Detachment Zone in a Crustal-scale Metamorphic Core Complex

Tectono-metamorphic history of the eastern Taureau shear zone, Mauricie area, Québec: Implications for the exhumation of the mid-crust in the Grenville Province

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