DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Author:||Simard et al., 2013|
|Type area:||Kuujjuaq and Ungava Bay area (NTS sheet 24K)|
|Geological province:||Churchill Province|
|Geological subdivision:||Rachel-Laporte Lithotectonic Domain|
The Freneuse Suite was introduced by Simard et al. (2013) in the Kuujjuaq and Ungava Bay area to group all Laporte Supersuite metasedimentary rocks. The Laporte Supersuite includes Paleoproterozoic volcano-sedimentary rocks of the Rachel-Laporte Lithotectonic Domain, which represents the eastern part of the New Quebec Orogen in the Southeastern Churchill Province (SECP). The Freneuse Suite was continued southward in the Saffray Lake (Lafrance et al., 2014) and Jeannin Lake (Charette et al., 2016) areas.
Metasedimentary rocks now assigned to the Freneuse Suite were first mapped by Sauvé (1957, 1959), Gélinas (1958a, 1958b, 1959), Fahrig (1964), Dimroth (1966), Dressler (1974, 1979), Baragar (1967), Frarey (1967), Penrose (1978), Clark (1978, 1980) and Girard (1995). These observations were incorporated into the SIGÉOM compilation map by Thomas Clark between 2009 and 2016 and used to supplement the description of several units.
The Freneuse Suite consists mainly of paraschists and various metasedimentary rocks (pPfru1) with lesser amounts of slightly metamorphosed mudstone, siltstone and mudslate (pPfru2), marble and calcosilicate rocks (pPfru3), iron formations (pPfru4), quartzite (pPfru5) and fragmented rocks interpreted as conglomerate or breccia (pPfru6).
The metasedimentary rock unit of the Freneuse Suite (pPfru1) consists of homogeneous, granoblastic, and fine-grained rocks that usually display millimetric to centimetric banding. This banding, marked by variations in composition (proportion of micas) and grain size (finer in less micaceous bands) of the rock, may represent primary bedding. Compared to Core Zone metasedimentary rocks, Freneuse Suite metasedimentary rocks were not (or very little) affected by the migmatization phenomenon associated with a major regional melting event. Partial melting evidence is still recognized locally in thin sections. Unit pPfru1 is commonly cut by quartz veins subconformable to foliation. These veins are dismembered, boudinaged and folded. Metasedimentary rocks contain biotite and muscovite flakes that define primary foliation. The latter is often undulating and is affected by a second foliation (crenulation cleavage) marked by coarser mica flakes, indicating the existence of two generations of micas. In places, the foliation is at an angle with compositional banding. Chlorite, altering biotite, and garnet are frequently observed, whereas amphiboles are sparse and only present in certain beds.
In thin sections, quartz and plagioclase have completely recrystallized. In some places, 5-25% K-feldspar is also observed as lenticular clusters or poikiloblasts. Garnet forms euhedral to subhedral millimetric poikiloblasts, locally elongated in foliation or deviant. These crystals show pressure shadows and generally aligned quartz, plagioclase and mica inclusions, indicating syn-kinematic to late kinematic growth. Garnet overlaps with biotite and also occurs as small skeletal crystals scattered in the matrix. The main accessory minerals observed in metasedimentary rocks are opaque minerals, apatite and tourmaline with, more locally, sillimanite (fibrolite), zircon (as inclusions in biotite and chlorite), epidote, calcite, dark green spinel and sphene.
Simard et al. (2013) divided unit pPfru1 into eight subunits, respecting informal lithological subdivisions proposed by Thomas Clark in SIGÉOM compilation maps. These subunits are based on structural, mineralogical or lithological characteristics and include: 1) biotite-muscovite ± garnet ± sillimanite ± kyanite ± staurolite paraschist (pPfru1a); 2) homogeneous biotite-muscovite ± garnet ± sillimanite metawacke and meta-arenite (pPfru1b); 3) biotite-sillimanite ± muscovite ± garnet paraschist and paragneiss (pPfru1c); 4) biotite-garnet ± muscovite paraschist and paragneiss (pPfru1d); 5) biotite-muscovite paraschist and quartzitic paraschist with abundant amphibolite (pPfru1e); 6) garnet-biotite paraschist with abundant amphibolite (pPfru1f); 7) biotite-muscovite paraschist with some quartzite and marble beds (pPfru1g); and 8) biotite-carbonate ± chlorite schist (pPfru1h). These different subunits are generally interstratified and have not always been able to be individualized during 1:250 000 scale mapping, particularly with respect to subunits pPfru1e to pPfru1h located primarily from previous work. Apart from the presence of secondary lithologies or specific minerals, metasedimentary rocks of subunits pPfru1c to pPfru1h are similar to those of subunits pPfru1a or pPfru1b described below.
Freneuse Suite 1a (pPfru1a): Paraschist
Paraschist of subunit pPfru1a is silver-grey or bluish grey in fresh exposure and beige or light grey in altered patina. It contains a significant amount of muscovite (15-35%) and brown biotite (10-25%) flakes. Locally, schist is characterized by varying amounts of garnet (2-40%), sillimanite, staurolite or kyanite.
When present, sillimanite forms whitish nodules 0.5-2 cm (Simard et al., 2013); this assemblage probably represents a retrogressive transformation of ancient andalusite porphyroblasts. Sillimanite also occurs as prismatic crystals aligned with the main foliation or crenulation cleavage. Staurolite forms poikiloblasts containing aligned quartz ± opaque mineral inclusions. Sparser, kyanite typically occurs as porphyroblasts fractured and elongated in foliation. It locally contains quartz inclusions. Chlorite is also observed as an alteration phase of staurolite, as well as at the edge of kyanite crystals.
Freneuse Suite 1b (pPfru1b): Homogeneous Metawacke and Meta-Arenite
Metasedimentary rocks of subunit pPfru1b are grey in fresh exposure and very light grey in altered surface. Protoliths are probably arkosic and lithic wackes. However, the presence of meta-arenite is also common. Micas, less abundant than in paraschist, consist of brown to reddish brown biotite (10-20%) and muscovite (2-10%) generally concentrated in millimetric laminae. In the Saffray Lake area (Lafrance et al., 2014), rocks are more deformed in the vicinity of the Lac Turcotte Fault and regularly display a mylonitic texture with quartz bands. In the Jeannin Lake area (Charette et al., 2016), 5-10 km north of Nachicapau Lake, laminated outcrops resembling intermediate tuffs were also assigned to subunit pPfru1b. Finally, this subunit also includes beds containing lenticular fragments of mafic or felsic rocks that could represent lapilli metatuffs or lithic metawackes.
In addition to klippes drawn on the map, unit pPfru2 also forms non-mappable decimetric beds interstratified with metasedimentary rocks of unit pPfru1. The rock is weakly metamorphosed, aphanitic and dark grey to black, locally bluish. It consists of a very finely recrystallized feldspar-quartz-mica matrix containing coarser crystals of biotite, garnet and opaque minerals, mainly graphite and sulphides. Chlorite, apatite and zircon are accessory phases observed in thin sections.
Unit pPfru3 consists of marble (pPfru3a) and calcosilicate rocks (pPfru3b) which typically occur in discontinuous beds a few hundred metres thick. These beds are mainly located near large thrust faults, as well as near faulted contacts of the Boulder and Rénia complexes in the Kuujjuaq area (Simard et al., 2013). They could represent decollement surfaces that would have facilitated movement along these faults. These lithologies also form centimetric to decimetric beds and boudins in metasedimentary rocks of unit pPfru1, as well as in mafic rocks of the Klein Suite. On outcrops, unit pPfru3 rocks show a characteristic surface marked by millimetric to centimetric ridges and furrows due to differential erosion of beds more or less rich in carbonates or silicates.
Freneuse Suite 3a (pPfru3a): Impure Marble and Dolomitic Marble
Marble of subunit pPfru3a is homogeneous, fine to coarse grained and whitish grey with a light, beige or orange grey altered surface. It is generally quite pure and composed of completely recrystallized carbonate with a few quartz lenses and phlogopite layers, possibly representing primary bedding. In other areas, marble is impure and contains some tremolite, diopside or wollastonite (Gélinas, 1958a, b). Accessory minerals are sphene, zircon and apatite. High magnesium contents indicate that marble is composed of a mixture of dolomite and calcite.
Freneuse Suite 3b (pPfru3b): Calcosilicate Rocks
Calcosilicate rocks of subunit pPfru3b are more heterogeneous, white, grey or green, and show significant variations in composition. They are mainly composed of feldspar, diopside, carbonate, amphibole (tremolite or hornblende) and quartz. The quartzofeldspathic matrix is granoblastic or as anhedral clusters surrounding ferromagnesian minerals. These frequently occur as large poikilitic crystals. Diopside is replaced by amphiboles. Calcosilicate rocks contain phlogopite (<8%), sphene (<4%) and, in smaller amounts, apatite, zircon, garnet and opaque minerals. Alteration minerals, such as zoisite, scapolite and chlorite, have been observed in places.
Iron formations consist of three generally interstratified facies: 1) silicate facies iron formations (pPfru4a); 2) sulphide facies iron formations (pPfru4b); and 3) carbonate facies iron formations (pPfru4c). The silicate facies is the most common. All silicate and carbonate facies iron formation klippes were observed in the Kuujuaq area (Simard et al., 2013), whereas the two occurrences of sulphide facies iron formation are in the Jeannin Lake area (Charette et al., 2016).
Sauvé and Bergeron (1965) describe ferriferous units in the Thévenet Lake area (sheet 24K03) as rocks composed of quartz, magnetite, garnet, Fe-amphibole and Fe-carbonate. This latter phase is only abundant in two carbonate facies iron formation klippes (pPfru1c) located NE of Rachel Lake.
Freneuse Suite 4a (pPfru4a): Silicate ± Oxide Facies Iron Formation
Silicate facies iron formations are generally well banded and consist of alternating light (quartz) and dark (quartz-magnetite or garnet-amphibole ± magnetite) bands. Amphiboles occur in large grains and radial aggregates. Sauvé and Bergeron (1965) describe two types of amphiboles, one resembling hornblende and another resembling grunerite. The two amphiboles appear to be stable in the presence of each other and are occasionally intergrown. Accessory minerals are biotite, chlorite, apatite and tourmaline. Beds of grunerite schist, oxide facies iron formation and metachert are interstratified with the silicate facies.
Freneuse Suite 4b (pPfru4b): Sulphide Facies Iron Formation
Sulphide facies iron formations, including beds interstratified with the silicate facies, are characterized by a brecciated texture consisting of 15-35% millimetric to centimetric subrounded to subangular fragments of quartzofeldspathic rocks, chert and quartz in a very fine-grained and highly magnetic dark matrix. The matrix is mainly composed of pyrrhotite with lower amounts of graphite and pyrite. The latter occurs as subhedral crystals (1-4 mm).
In addition to klippes of unit pPfru5 drawn on the map, small quartzite beds were observed within other units of the Laporte Supersuite. Quartzite is a finely recrystallized holohyaline rock, whitish, greenish or pinkish, which contains some muscovite or chlorite. It displays millimetric to centimetric bedding marked by muscovite laminae or small hematitized beds. It is cut by 2-10% millimetre to decimetre-wide quartz veins, often boudinaged. Some impure quartzite beds contain millimetric to decimetric biotite-muscovite schist beds.
Unit pPfru6 is located between the Boulder and Rénia complexes in the Kuujjuaq area (Simard et al., 2013). The rock is highly deformed and contains very stretched fragments 5-30 cm long by 1-8 cm wide. Gélinas (1958a) describes this unit as conglomerate or breccia with quartz and feldspar pebbles and fragments in a matrix rich in amphibole and epidote.
The Freneuse Suite is the main unit of the Laporte Supersuite in the Rachel-Laporte Lithotectonic Domain. It is generally 25-40 km wide and oriented NW-SE. This unit thins in the extreme north of the SECP (~3 km), as well as in the vicinity of the Archean Rénia, Highfall and Wheeler complexes. Subunits pPfru1a and pPfru1b are the main units of the Freneuse Suite. Paraschists of subunit pPfru1a dominate in the northern part of the Rachel-Laporte Domain, in the Kuujjuaq area (Simard et al., 2013) and northern Saffray Lake area (Lafrance et al., 2014), where they form a metasedimentary sequence ~12 km wide by 170 km long. Another large sequence, ~10 km wide by 70 km long, was recognized farther south in the Jeannin Lake area (Charette et al., 2016). Smaller strips were also observed between the two sequences. Subunit pPfru1b mainly outcrops in the south-central part of the Rachel-Laporte Domain where it forms a sequence of more than 250 km long by 30 km wide. This subunit thins on the edge of the Wheeler Complex like the rest of the Freneuse Suite.
Subunit pPfru1c was observed in the Kuujjuaq area (Simard et al., 2013) and the northern Saffray Lake area (Lafrance et al., 2014). It is located primarily near the eastern edge of the Rachel-Laporte Domain where it forms a strip ~85 km long by 0.5-3 km wide. Subunit pPfru1d also forms a few hectometric to kilometric strips in the Kuujjuaq and Saffray Lake areas, while subunit pPfru1e forms two strips 15-20 km long and <1 km wide in the central part of the Kuujuaq area. Subunit pPfru1f forms two hectometric klippes in the Boulder Complex area (Simard et al., 2013). Subunit pPfru1g is observed exclusively in the Ballantyne Lake area (sheet 24K11; Sauvé, 1959), where it forms strips a few kilometres wide within paraschist sequences (pPfru1a). Finally, subunit pPfru1h was mapped by Dressler (1974) in the Marcel Lake area (sheet 24C16), near the Lemoyne Complex carbonatite.
Unit pPfru2 is mostly in contact with units of the Labrador Trough, where it forms strips several tens of kilometres long and a few kilometres wide. Units pPfru4 and pPfru5 generally form small hectometric klippes continuous over a few kilometres in the Rachel-Laporte Domain. However, larger quartzite sequences (pPfru5) were observed in the southern portion of the Jeannin Lake area (40 km x 3 km), near the SW edge of the Rénia Complex (10 km x 3 km), and immediately south of Horseshoe Lake (8 km x 1.5 km). Finally, unit pPfru6 consists of two close klippes, 5-10 km long and <500 m wide, located between the Rénia and Boulder complexes, in the Thévenet Lake area (Gélinas, 1958a).
Several authors have proposed that Freneuse Suite metasedimentary rocks mostly represent equivalents of Kaniapiskau Supergroup metasedimentary rocks located in the Labrador Trough just to the west. (Harrison, 1952; Gélinas, 1958a, b; Sauvé and Bergeron, 1965; Simard et al., 2013). However, mapping work by Charette et al. (2016) indicates that metasedimentary rocks of the Laporte Supersuite are distinguishable from those of the Labrador Trough by a greater apparent thickness and a more homogeneous composition.
In the Thévenet and Gabriel lakes areas, Gélinas (1958a, b) mentioned that the paraschist subunit (pPfru1a) might correspond in part to the Thévenet Formation of the Labrador Trough. In the area adjacent to the west, Sauvé and Bergeron (1965) propose that most of metasedimentary rocks now assigned to the Freneuse Suite are equivalent to the Baby Formation, consisting of pellitic rocks, quartzite and ferriferous rocks. The Baby Formation was assigned to the Koksoak Group (Wares and Goutier, 1990), associated with the second deposition cycle of the Kaniapiskau Supergroup, which was between 1884 Ma and 1870 Ma (Clark and Wares, 2004). Carbonate rocks of the Freneuse Suite (pPfru3) could be equivalent to older dolomitic rocks of the Denault Formation (Harrison, 1952), which is the lower part of the Attikamagen Group (Clark & Wares, 2004) associated with the end of the Labrador Trough’s first cycle.
Rocks of the Freneuse Suite are commonly interstratified with amphibolites and mafic and ultramafic intrusions of the Klein Suite. The Freneuse Suite is in fault contact with various Archean or Proterozoic complexes (thrust sheets) of the Rachel-Laporte Domain, namely the Boulder, Rénia, Highfall, Boullé, Wheeler and Giton complexes. (Simard et al., 2013; Lafrance et al., 2014; Charette et al., 2016). The various Klein units are also locally intruded by granite and pegmatitic granite dykes or sills of the Mercier Suite.
Does not apply.