The Churchill Province was defined by Stockwell (1961) as a tectonic province of the Canadian Shield. It included, among others, the area between the Superior and Nain provinces in northeastern Quebec. Later, Hoffman (1988) viewed this area as a southern extension of the Archean Rae Province, much of which is in the Northwest Territories. In the first regional synthesis, presented at the GAC-MAC in 1987 (Trans-Hudson Symposium; van der Leeden et al., 1990; Wardle et al., 1990b; Hoffman, 1990), the term “Eastern Churchill Province” was chosen for the area affected by the Husonian Orogen. This division then included the New Quebec Orogen to the west, the Torngat Orogen to the east and, according to the author, the Rae Province (Hoffman, 1990) or the “Central Division” (Wardle et al., 1990b) in the centre. Hoffman (1990) notes, however, that the correlation with the Rae Province is uncertain and based primarily on structural orientation. James et al. (1996) renamed the central portion “Core Zone”. The definition of the latter was an amalgamation of remobilized Archean rocks, some of which would have an affinity with the Superior and Rae provinces. St-Onge et al. (1998) subsequently demonstrated that the Trans-Hudsonian Orogen (Stockwell, 1961) extended well into southern Baffin Island, thus rejecting any possible connection to the Rae Province.
The term “Southeastern Churchill Province (SECP)” appears to have been first used by James et al. (1996). It has been repeated in a number of subsequent publications, including that of Wardle et al. (2002), which presents a SECP regional synthesis. This stratigraphic record describes only the Quebec portion of the SECP.
In Quebec, Canada, the Southeastern Churchill Province is located in the northeastern part of the province. It is 415 to 615 km long, 250 to 380 km wide and has a NNW-SSE general orientation. It is bordered to the west by the Archean Superior Province, to the east by the Archean to Paleoproterozoic Nain (North Atlantic Craton and Burwell Lithotectonic Domain) and Makkovik provinces and to the south by the Proterozoic Grenville Province. This part of the Churchill Province is a branch of the Trans-Hudsonian Orogen, which represents a large Paleoproterozoic orogenic belt that extends from central United States to Greenland.
The SECP consists of several lithotectonic blocks of different origins that have been amalgamated by tectonic processes, the latest events being related to the Trans-Hudsonian Orogen. It has been affected to the west and east by the New Quebec and Torngat orogens, respectively, which continue their overprinting in various domains grouped together under the term Core Zone. According to Lafrance et al. (2018), the latter represents a block that evolved during the amalgamation process. These authors consider it to include all lithological units located east of the Labrador Trough up to the Nain Province, represented in Quebec by the Burwell Lithotectonic Domain.
Different tectonic subdivisions of the SECP have been proposed by several authors; those of Wardle et al. (1990a) are the best known. Geological surveys and studies conducted by Government of Quebec and its partners between 2009 and 2017 have resulted in the redefinition of six lithotectonic domains as part of the SECP synthesis (Lafrance et al., 2018). These domains were determined from the main lithologies, large structures cutting the SECP and geochronological and metamorphic data.
From west to east, the proposed SECP lithotectonic domains are the Labrador Trough and the Rachel-Laporte, Baleine, George (Charette et al., 2018), Mistinibi-Raude (Charette et al., 2019) and Falcoz lithotectonic domains.
The Labrador Trough is a metamorphosed volcano-sedimentary belt (greenschist to amphibolite facies) of Paleoproterozoic age (2.17-1.87 Ga), folded and overthrusted on the Superior Craton during the New Quebec Orogenesis. It extends over a length of more than 850 km, from the Grenville Province in the south to Ungava Bay in the north. Contact with the Superior Province in the west is mainly represented by the Maraude Fault. Contact with the Rachel-Laporte Lithotectonic Domain, in the east, is rather marked by various echelon faults running from north to south, namely the Pointe Reef, Lac Hérodier and Lac Keato faults.
The Rachel-Laporte Lithotectonic Domain consists of Paleoproterozoic metamorphosed volcano-sedimentary rocks (amphibolite facies) of the Laporte Supersuite (<1.84 Ga; Henrique-Pinto et al., 2017), previously interpreted as equivalent to the Labrador Trough (Fahrig, 1965; Poirier et al., 1990; Wardle et al., 2002; Simard et al., 2013). Subsequent mapping indicates instead that the Laporte Supersuite metasedimentary rocks differ from those of the Labrador Trough by greater apparent thickness and more homogeneous composition. Detrital geochronological data from Henrique-Pinto et al. (2017) also indicate that these two sedimentary basins are derived from distinct tectonic sources and environments. The author’s work indicates that detrital zircons of the Kaniapiskau Supergroup units (Labrador Trough) have a signature typical of the Superior Province (maximum frequency around 2.72 Ga). In the case of the Laporte Supersuite, the maximum frequency of detrital zircons is more around 1.84 Ga, suggesting that the main source of sediment comes from SECP units. The Rachel-Laporte Domain also includes Archean structural complexes (imbricate blocks not belonging to the Laporte Supersuite), interpreted as having belonged to the Superior Province (Wardle et al., 2002), as well as tectonic slices exhaled during thrusting of the Baleine Lithotectonic Domain on the Rachel-Laporte Domain and Labrador Trough.
The Baleine Lithotectonic Domain consists of two sections (north and south), the boundary of which is approximately 30 km south of Kuujjuaq. The northern section consists mainly of Archean tonalitic gneiss (Ungava Complex; 2.7-2.9 Ga), migmatite (Qurlutuq Complex) and anatectic granite (Aveneau Suite) derived from partial melting of gneiss. It also includes a mafic to intermediate intrusive complex (Kaslac Complex) and volcano-sedimentary sequences (Curot and Akiasirviup Suite) alternating with gneiss in its western part. The southern section includes a large, highly migmatitized supracrustal cover (False and Winnie suites), deformed Archean potassic units (Saffray Suite; 2.7 Ga), but also gneiss, migmatites and anatectic granites similar to those observed in the northern section. A metamorphosed potassic intrusion (Champdoré Suite), synchronous to the De Pas Supersuite (see George Domain below), is also present in the southern part of the domain. The southern portion of the Baleine Domain is also characterized by a domes and basins structural pattern (Charette et al., 2016).
The George Lithotectonic Domain is dominated by Paleoproterozoic intrusions of the De Pas Supersuite (1.86-1.8 Ga), which have been emplaced within gneiss units and their partial melting products (Saint-Sauveur and Guesnier complexes; 2.6-2.7 Ga) and through a large Neoarchean metamorphosed volcano-sedimentary sequence (Tunulic Complex; 2.6-2.7 Ga). Limited by major shear zones to the west (Tudor Lake) and east (Rivière George), this domain is characterized by large mylonitic deformation zones. Lafrance et al. (2018) consider the George Domain to be a transition zone between tectonometamorphic overprinting of the New Quebec and Torngat orogens. Thus, this domain would represent a discontinuous or gradual transition between their contrasting orogenic styles.
The Mistinibi-Raude Lithotectonic Domain stands out in the near absence of Archean lithologies, with the oldest units bordering the Neoarchean and Paleoproterozoic (2.3-2.5 Ga), and the absence of magmatism around 1.8 Ga. It includes a large sequence of paragneiss and diatexite (Mistinibi Complex), metavolcanic rock units (Ntshuku and Zeni complexes), gneiss (Advance and Bourdon complexes) and a clastic metasedimentary sequence (Hutte Sauvage Group). The Mistinibi-Raude Domain is also characterized by the presence of numerous intrusions, mostly potassic, whose composition varies from felsic to mafic. Some of these intrusions have crystallized during the Paleoproterozoic and Neoarchean (Pelland, Nekuashu and Dumans suites). However, the majority of these intrusions are Mesoproterozoic and have been emplaced at the boundary between the SECP and Nain Province (Mistastin Batholith, Michikamau and Napeu Kainut suites). Charette et al. (2019) also include, in this domain, the Orma Domain, which represents an area south of the Zeni Shear Zone, considering that these two areas are characterized by the absence of crystallization age greater than 2.67 Ga, but mostly by the absence of metamorphic overprinting associated with the Trans-Hudsonian Orogen.
The Falcoz Lithotectonic Domain represents the SECP’s eastern margin divided into two parts (west and east) and separated by the Blumath Shear Zone, which marks the passage of the upper amphibolite facies to the granulite facies. The western part is dominated by variously migmatitized gneiss (Kangiqsualujjuaq and Fougeraye complexes) and potassic intrusions (Siimitalik Suite), mostly Mesoarchean (2.7-3.0 Ga). It also includes a sequence of Paleoproterozoic metamorphosed volcano-sedimentary rocks (Lake Harbour Group) intruded by mafic to ultramafic dykes and sills (Nuvulialuk Suite). The eastern part of the Falcoz Domain is dominated by Archean granulitic orthogneiss (Sukaliuk Complex; 2.7-2.9 Ga) and Paleoproterozoic hypersthene intrusions (Inuluttalik Suite; 1.8 Ga). More to the east, this domain also includes intrusive rocks interpreted as the root of a magmatic arc emplaced on the SECP eastern margin around 1877 Ma (Bertrand et al., 1993). These rocks are grouped within the Lomier Complex, which includes supracrustal rocks (Koroc River Group), charnockitic intrusions (Courdon Suite) and gneiss interpreted as being derived from the Koroc River Group and Courdon Suite deformation and alternation.
All SECP lithotectonic domains are cut by Mesoproterozoic subophitic dykes (~1.3 Ga) which have been grouped into swarms of varying direction, the main ones being the Falcoz Swarm (NNW-SSE), Slippery Dykes (E-W) and Harp Dykes (NE-SW).
Recent work by the Ministère and its partners of the Geological Survey of Canada and the academic community has identified six distinct lithotectonic domains within the SECP (see section above). These lithotectonic domains geological evolution is closely linked to the convergence context of the Trans-Hudsonian Orogen involving the assembly of various Archean continental masses to the Superior Craton (Hoffman, 1988). Specifically, the Torgnat Orogen (1.89-1.81 Ga) joins the SECP to the North Atlantic Craton, and the New Quebec Orogen (1.82-1.77 Ga) joins the SECP to the Superior Craton (Wardle et al., 2002; Charette, 2016). Mapping reveals the widespread presence of migmatites throughout the SECP, with the exception of the Rachel-Laporte Domain (Simard et al., 2013; Lafrance et al., 2014, 2015, 2016; Charette et al., 2016). In addition, metamorphic petrochronology indicates that the Torngat Orogen tectonometamorphic overprinting is not limited to granulitic rocks observed in the eastern Falcoz Lithotectonic Domain (Charette, 2016), such that the extent and timing of SECP orogens can only be partially resolved by mapping. Since orogen overprinting likely affects the six lithotectonic domains in various ways, the use of the terms “Torngat Orogen” and “New Quebec Orogen” as lithotectonic divisions is being abandoned in favour of a classification based on domain origin (Lafrance et al., 2018).
Progress in understanding the geological evolution of the SECP require more constraints on the extent of the New Quebec and Torngat orogens, as well as characterization of pressure-temperature-time (PTt) trajectories and structural styles. Current knowledge highlights a gradual metamorphic gradient through the entire Falcoz Domain and a slow erosional exhumation (Charette, 2016). As for the structural style, the George, Mistinibi-Raude and Falcoz domains are all affected by subvertical shear zones. Of these, the Rivière George and Moonbase shear zones are conjugate and show deformation temperatures that are consistent with activity under average crust conditions (Vanier et al., 2018). Although piecemeal, this information suggests continuous tectonometamorphic overptinting from the North Atlantic Craton to the Baleine Domain.
Different tectonic evolution models have been proposed in recent years (for more details, see Lafrance et al., 2018).