Van der Leeden et al. (1990) proposed different tectonic subdivisions for the Southeastern Churchill Province (SECP), including the Mistinibi-Raude Domain, located between the Rivière George (ZCrge) and Moonbase (ZCmob) shear zones. Other authors have also used the terms “Central zone” (James and Mahoney, 1994), “Central Gneissic Zone” (Wardle et al., 1990b) and “Mistinibi-Raude Gneissic Domain” to refer to this area. The term « Mistinibi-Raude Domain » was used by Wardle et al. (1990) and has been used by the scientific community since then. Recently, Corrigan et al. (2018) still used the term “Mistinibi-Raude Block” to define this area.

Geological surveys and studies conducted by the Ministère and its partners between 2009 and 2017 identified the regional boundaries of the Mistinibi-Raude Lithotectonic Domain. These have been redefined slightly as part of the synthesis of the Southeastern Churchill Province (Lafrance et al., 2018).

The Mistinibi-Raude Lithotectonic Domain is located in the southeastern part of the SECP. It has a diamond shape which measures ~290 km in length by 30 km to 70 km in width, for a total area of ~14 115 km². It is generally oriented N-S and limited to the east and south by the Labrador border. The Mistinibi-Raude Domain is limited to the west by the end of the ZCrge influence zone. It is therefore in fault contact with the George Lithotectonic Domain. On the NE side, it is limited by the ZCmob, which marks the contact with the Falcoz Lithotectonic Domain.

The Mistinibi-Raude Lithotectonic Domain is dominated by a Paleoproterozoic sequence of migmatized paragneiss and diatexite (Mistinibi Complex). It also includes gneissic bedrock (Elson, Jannière and Advance complexes) and Neoarchean intrusions, usually felsic (La Pinaudière Granite and Brass Intrusion). These Archean units (2678-2571 Ma) show evidence of partial melting; however, migmatization is less important than in other SECP lithotectonic domains, so no migmatite unit derived from melting of these rocks has been defined.

There are also two volcano-sedimentary sequences in the domain: the Zeni Complex, which age is on the Archean-Proterozoic limit (~2480 Ma), and the Ntshuku Complex, clearly Paleoproterozoic (~2373 Ma). Rocks of the Zeni Complex are concentrated within the Zeni Shear Zone (ZCzen). They are thus highly mylonitized, making it difficult to identify precursors. However, according to Danis (1991) and Taner (1992), the Zeni Complex contains a good proportion of volcano-sedimentary rocks. The Ntshuku Complex is much less deformed and interpreted as an ancient volcanic arc (Corrigan et al., 2018). A well-preserved and minimally deformed Paleoproterozoic metasedimentary sequence (<1973 Ma) (Hutte Sauvage Group) also forms a regional lenticular unit in the west-central part of the domain.

The Mistinibi-Raude Domain is characterized by a large proportion of intrusive rocks, mostly of intermediate to mafic composition, both Paleoproterozoic (2344-2312 Ma) and Mesoproterozoic (1482-1409 Ma). The Nekuashu Suite and the Lac Brisson pluton differ slightly from other intrusions by older (2515 Ma) and younger (1240 Ma) ages respectively. Archean to Paleoproterozoic units are foliated to locally mylonitic near influence zones of the Rivière George, Moonbase and Zeni shear zones. Mesoproterozoic units are massive and generally homogeneous.

Rocks of the Mistinibi-Raude Lithotectonic Domain have been grouped into different lithodemic units, mainly suites and complexes, according to the standards of the North American Stratigraphic Code (Ministère de l’Énergie et des Ressources, 1986; American Commission on Stratigraphic Nomenclature, 2005; Easton, 2009) and taking into account the nomenclature already established. These units were defined based on available geological and geochronological data. The stratigraphic order is shown on the geological map of Charette et al. (2019) and in the table below, from the youngest to the oldest unit.

Geological Evolution

The Mistinibi-Raude Lithotectonic Domain differs from the rest of the SECP by the small proportion of Archean units it includes and by crystallization ages (2.68-2.3 Ga) obtained in all of its units which are relatively uncommon in the rest of the SECP. The oldest ages (2678-2571 Ma; Nunn et al., 1990; James et al., 2003) were obtained in Labrador, more specifically south of the ZCzen. This zone is referred to by various authors as a distinct lithotectonic domain: the Orma Domain (Nunn and Noel, 1982; Nunn et al., 1990; Wardle et al., 1990; James et al., 2003; Hammouche et al., 2011, 2012; Corrigan et al., 2018). Given that these two zones are characterized by the absence of a crystallization age older than 2.67 Ga and, more importantly, the absence of a metamorphic footprint associated with the Trans-Hudsonian Orogen, Charette et al. (2019) preferred to pair this zone with the Mistinibi-Raude Domain as part of the SECP synthesis. While it is uncertain whether these two zones have a common origin, at least they have been amalgamated prior to the Trans-Hudsonian Orogen.

The geological evolution of the Mistinibi-Raude Domain is mainly marked by an intermediate to mafic magmatism between 2344 Ma and 2312 Ma, as well as by a period of erosion of these rocks. The latter produced an important sequence of sedimentary rocks, now recognized as the Mistinibi Complex and having a maximum deposition age of ~2220 Ma (Godet et al., 2018). The evidence of metamorphism under suprasolidus conditions between 2145 Ma and 2070 Ma, as well as the absence of metamorphic ages typical of the Trans-Hudsonian Orogenesis, indicates a tectonometamorphic evolution distinct from the rest of the SECP, as discussed by Charette et al. (2019). Subsequently, erosion of Mistinibi Complex migmatites and surrounding rocks produced the Hutte Sauvage Group sedimentary basin. The absence of geochronological data from detrital zircons that would coincide with crystallization of the De Pas Supersuite (1861-1805 Ma) suggests that the basin was formed prior to the emplacement of this magmatic arc unit.

The stratigraphic diagram presented by Charette et al. (2019) shows initial relationships between Neoarchean to Paleoproterozoic units, intrusions and Mesoproterozoic dykes.

References

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