The Paleoproterozoic southeastern Churchill Province (SECP) is located in the northeastern Canadian Shield of Labrador and Quebec. The SECP formed through the oblique collisions of the Archean Nain and Superior cratons with a third intervening Archean block, the core zone. The belt has a tripartite structure, comprising the Torngat Orogen (TO) formed by Nain craton -core zone collision in the east, the core zone in the centre, and the New Quebec Orogen (NQO) formed by Superior craton -core zone collision in the west. The SECP thus records transpressional development on the flanks of the Superior and Nain cratons as they indented northwards to form the larger Trans-Hudson -Nagssugtoqidian orogenic belt to the north. Principal stages of tectonic development were (1) 2.2-2.1 Ga crustal rifting of Nain and Superior cratons; (2) ca. 1.9 Ga subduction under eastern Nain craton; (3) ca. 1.87-1.85 Ga collision of Nain craton and core zone to form the TO; (4) 1.845-1.820 Ga sinistral transpression in the TO, and subduction under the western core zone; and (5) 1.82-1.77 Ga collision of Superior craton and core zone to form the NQO, in association with dextral transpression. Crustal-scale cross sections of the SECP have been developed from reflection and refraction seismic data. The western part of the NQO is dominantly west-vergent and associated with an imbricate thick-skinned thrust stack that ramps from the base of the crust. The core zone is characterized by a 35-40 km thick crust and pervasive east-dipping fabrics related to westerly thrusting. The TO is a narrow, doubly vergent belt, associated with a 48 km thick crust that forms a crustal root with a Moho relief of 12 km. The root is interpreted to result from attempted subduction of the core zone under the Nain craton, possibly as a result of mid-crustal wedging by the Nain craton. The TO was the site of intense convergence that resulted in excision of juvenile crust, possibly including tectonic removal of the axial magmatic arc. As a result, the middle to lower levels of the SECP consist largely of refractory Archean lithosphere. This may account for the lack of widespread post-collisional plutonism in the SECP and the preservation of the TO root. 663Résumé : Le sud-est de la Province de Churchill (SECP, Southeastern Churchill Province; Paléoprotérozoïque) est situé dans le nord-est du Bouclier canadien, au Labrador et au Québec. Le SECP a été formé par des collisions obliques entre les cratons archéens de Nain et du Supérieur et un troisième bloc archéen intermédiaire, la zone noyau. La ceinture a une structure tripartite, comprenant l'orogène Torngat (TO), formé par la collision entre la zone noyau et le craton de Nain, à l'est, la zone noyau au centre et l'orogène du Nouveau-Québec (NQO), formé par la collision entre la zone noyau et le craton du Supérieur, à l'ouest. Le SECP enregistre donc le développement de transpressions sur les flancs des cratons de Nain et du Supérieur alors que ces derniers se déplaçaient vers le nord pour former la grande ceinture orog...
As part of the Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT), Lithoprobe acquired 1250 km of deep seismic reflection data along the coast of Labrador and across Ungava Bay, to image evidence of Proterozoic crustal accretion to the Archean nuclei of the Nain and Superior provinces of the Canadian Shield. The relatively pristine Archean crust of the Nain Province has low reflectivity and generally lacks systematic reflector orientations. Reworking of Archean crust on the margins of the Makkovik Province has little effect on this weak signature. In contrast, the Archean crust in the Eastern Churchill (Rae) Province appears to have been overprinted by a strongly developed, whole-crustal, easterly dipping reflection fabric, interpreted to result from Proterozoic collision of the Nain and Superior provinces in the paired New Quebec and Torngat orogens. Juvenile Proterozoic crust in the Makkovik and Grenville provinces also shows strong whole-crustal dipping reflection fabrics, interpretable as outwardly verging structures associated with collisional mobile belts. Crustal thickness varies from 35 to 45 km in Proterozoic provinces, except where thinner in areas probably affected by Mesozoic extension associated with rifting of the Labrador Sea. Dipping reflectors in the mantle are commonly associated with strong lower-crustal dipping reflections in a manner similar to that observed in some modern orogens. The ECSOOT data show that Proterozoic crust in this area has structural forms comparable with those of modern orogens and, inferentially, its tectonic development was controlled by very similar collisional processes.
The Makkovik Province of Labrador represents the extension of the Ketilidian Mobile Belt of south Greenland into mainland North America; it exhibits a threefold division into a foreland region, a fold-and-thrust belt, and an interior magmatic zone. The Kaipokok Domain is dominated by Archaean basement rocks that form an extension of the North Atlantic Craton, but Proterozoic reworking is recorded by the reorientation of a c . 2230 Ma dyke swarm. Supracrustal rocks, consisting of shallow-marine sedimentary rocks overlain by greywackes and mafic volcanic rocks, rest unconformably upon Archaean basement, but towards the interior of the belt the basal unconformity is eradicated by northwest-directed thrusting. In the Aillik Domain , highgrade supracrustal rocks of similar aspect to those of the Kaipokok Domain are separated from the basement by mylonite zones, in a thick-skinned fold-and-thrust belt ( Kaipokok Bay Structural Zone ), believed to record significant northwest-directed translation. The Aillik Domain also contains abundant felsic volcanic rocks that lack typical arc-like geochemical signatures. The Cape Harrison Domain is dominated by plutonic rocks, including suites of 1840 Ma, 1800 Ma, 1720 Ma and 1650 Ma age, but gneissic inliers apparently represent ‘juvenile’ Proterozoic crust. The dominant 1800-1720 Ma plutonic suites are late-orogenic to post-orogenic, siliceous, potassic granitoid rocks, which resemble Phanerozoic post-collisional suites, rather than subduction-related arc batholiths. Nd isotopic variations position the eastern edge of the North Atlantic Craton close to the boundary between the Aillik and Cape Harrison Domains. The structural evolution of the Makkovik Province records a shift from pre- 1800 Ma northwest-directed thrusting to post-1800 Ma tight upright folding, also northwest-verging. However, there is also evidence for earlier (pre- 1890 Ma) events in the Kaipokok Domain. Major unresolved problems include the timing of early sub-horizontal deformation (perhaps related to collisional events), the age relations and setting of supracrustal sequences, the location of suture zones, the absence of clear arc-like magmatic assemblages, and the nature and antiquity of the eastern juvenile crustal block.
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