|Author:||Verpaelst et al., 2000|
|Type area:||Koroc River area (NTS sheet 24I)|
|Geological province:||Churchill Province|
|Geological subdivision:||Torngat Orogen|
The Sukaliuk Complex was introduced by Verpaelst et al. (2000) in the Koroc and Hebron River area (NTS sheets 24I and 14L) to describe a package of orthogneiss, supracrustal rocks and mafic rocks for the most part metamorphosed to the granulite facies and part of the Torngat Orogen, i.e. the area east of the Blumath Deformation Corridor (BDC). Part of this complex was assigned to the Lomier Complex by Girard (1990) during 1:50,000 mapping of the Courdon Lake area (sheet 14E12). Granulitic rocks present west of the Lac Pilliamet Shear Zone (LPSZ) were reassigned to the Sukaliuk Complex by Lafrance et al. (2015), as were the rocks mapped by Verpaelst et al. (2000) in the area directly to the north.
Climatic conditions of the summer of 1998 limited the fieldwork and resulted in Verpaelst et al. (2000) not always being able to differentiate granulitic gneiss of the Sukaliuk Complex by composition. They had thus grouped much of the Sukaliuk Complex in an undifferentiated granulitic gneiss unit. This subdivision was not used by Lafrance et al. (2015, 2016) in the southbound extension as the work of these authors allowed the Sukaliuk Complex to be subdivided according to its dominant composition. The regional synthesis of the entire southeastern Churchill Province (SECP; Lafrance and Charette, 2018), summer 2017 field checks in the Koroc River and Hébron area, and staining of samples collected during the summers of 1998 and 2017 have helped to standardize the nomenclature of this unit based on its dominant composition (Mathieu et al., 2018), and to abandon the undifferentiated granulitic gneiss unit.
As part of the regional synthesis of the SECP (Lafrance and Charrette, 2018), the seven (7) known units were reduced to five (5) informal units (ApPsuk1 to ApPsuk5). These changes in the nomenclature are detailed in the table below.
The Sukaliuk Complex is divided into five (5) informal units: 1) a hypersthene tonalitic orthogneiss unit (ApPsuk1); 2) a hypersthene granitic orthogneiss unit (ApPsuk2); 3) a unit of mafic and ultramafic rocks (ApPsych3); 4) a unit of metasedimentary rocks (ApPsuk4); and 5) a garnet felsic intrusion unit (ApPsuk5). The various units of the Sukaliuk Complex are cut by intrusive rocks of the Inuluttalik Suite (pPina) and often contain decimetric to metric horizons of other units of the Sukaliuk Complex.
Unit ApPsuk1 is the main unit of the Sukaliuk Complex. The fine to medium-grained rock is characterized by a greenish grey colour in fresh exposure, typical of orthopyroxene rocks, and a whitish to light grey colour in altered surface. It also shows a well-developed even-grained granoblastic texture. Gneiss banding is often difficult to observe, especially in fresh exposure; however, stains highlight alternating millimetric to centimetric bands of tonalite and quartz diorite (12-25% quartz). This banding is also defined by the presence of a coarser-grained leucocratic phase in diffuse bands, millimetric to centimetric, brown sugar in colour or lighter green. These bands could represent leucosomes, late intrusions, or the result of metamorphic segregation or metamorphic fluid circulation. Most of the outcrops of the Sukaliuk Complex are covered with lichen, which makes it difficult to properly recognize the presence of this enderbitic or, more rarely, charnockitic phase. Gneiss is also intruded to varying degrees by enderbite (in places charnockite) of the Inuluttalik Suite. These intrusions, similar to the leucocratic bands described above, are also in diffuse contact with the gneiss and are difficult to distinguish in outcrop. Sawed samples allow for a better distinction between the two phases. Gneiss contains between 1 and 25% stretched enclaves or centimetric to decimetric horizons of orthopyroxene diorite or granoblastic gabbronorite.
The ApPsuk1 gneiss contains 5 to 20% biotite and hypersthene, but green hornblende and clinopyroxene are also commonly observed, particularly in quartz diorite horizons. Biotite shows intense pleochroism from yellowish to dark brown-red. Hypersthene is usually fresh, in places altered to serpentine (especially iddingsite) or transformed into a mixture of hornblende and actinolite. Smoked quartz forms bands or discontinuous millimetric rods and has a strong undulatory extinction. K-feldspar (≤5%) is observed locally in small interstitial crystals. Opaque minerals (especially magnetite) and apatite are still present (2-5%). Other accessory minerals (epidote, garnet, sphene, allanite, zircon and calcite) are observed in small amounts.
Coarser-grained bands observed in gneiss contain centimetric euhedral orthopyroxene and well-developed quartz rods, giving them a deformed leucosome appearance. Although evidence of partial melting has been extensively identified on the outcrops visited in the Sukaliuk Complex, little evidence of this process can be seen in thin section. It is possible that the majority of partial melting textures were obliterated during deformation following migmatitization. The deformation style and absence of flow textures suggest that these units did not contain significant rheological contrast during the deformation event, excluding the possibility that a large proportion of leucosome was present at that time. A migmatitization episode likely occurred in the early stage of the Torngat Orogen, during which partial melting fluid extraction was effective. This explains the preservation of granulite facies paragenesis due to anhydrous conditions generated by liquid extraction (Charette, 2016).
Sukaliuk Complex 1a (ApPsuk1a): Tonalitic Orthogneiss
In some areas, the tonalitic gneiss does not contain hypersthene and is metamorphosed to the amphibolite facies. Several of these areas are bordered by fault zones, including the Lac Pilliamet Shear Zone (LPSZ), and may be associated with retrograde metamorphism to the amphibolite facies. On the other hand, there are also metric horizons of tonalitic gneiss interbedded with orthopyroxene gneiss, suggesting that the initial composition of the rock may explain the presence or absence of hypersthene. The gneiss composition of subunit ApPsuk1a varies from tonalite to quartz diorite. The rock is grey, non-magnetic and contains between 5 and 20% centimetric to decimetric enclaves or horizons of hornblende-biotite diorite. It also contains 5 to 15% bands or conformable centimetric dykes of coarser-grained pink granite. Quartz (10-25%) forms bands near deformation zones. Mafic minerals (7–20%) mostly consist of brown biotite with hornblende and magnetite more locally. Accessory minerals are scarce and consist of K-feldspar, apatite, chlorite, epidote, hematite and zircon.
Sukaliuk Complex 1b (ApPsuk1b): Banded Granulitic Gneiss with Alternating Tonalitic and Granitic Bands
Subunit ApPsuk1b is a minor component of the Sukaliuk Complex. It is composed of orthopyroxene gneiss showing alternating millimetric to centimetric bands of either tonalitic or granitic composition. The grey-brow sugar colour in fresh exposure and beige patina, regardless of the composition of bands, are characteristic. Only the variable proportion of mafic minerals (~5% for granitic bands and 10-25% for tonalitic bands) allows for individualization of band types in outcrop. Rocks of unit ApPsuk1b unit contain the same mineral phases and have the same textures as the ApPsuk1 unit.
In outcrop, unit ApPsuk2 is difficult to distinguish from unit ApPsuk1. Generally, the rock has slightly lighter green or brown sugar colour and contains few mafic minerals (5-10%). Stains highlight alternating granitic and granodioritic bands in gneiss. With the exception of K-feldspar, rocks of the ApPsuk2 unit contain the same mineral phases and have the same textures as the ApPsuk1 unit.
Sukaliuk Complex 2a (ApPsuk2a): Granitic Orthogneiss
Like unit ApPsuk1, unit ApPsuk2 also includes areas showing retrograde metamorphism to the amphibolite facies. The majority of these areas also appear to be associated with the presence of large shears in the vicinity of the LPSZ. This granitic gneiss, similar to that observed in the Kangiqsualujjuaq Complex (ApPkan2), is finely recrystallized, light grey and contains 5 to 30% millimetric bands of pink granite, slightly coarser-grained but also granoblastic. It also contains 25-40% K-feldspar, 20-25% quartz and 5-12% mafic minerals. The majority of these are brown biotite, in places chloritized with a few green hornblende more locally. The main accessory minerals are apatite and opaque minerals.
Unit ApPsuk3 includes all the intrusive or extrusive mafic and ultramafic rocks of the Sukaliuk Complex. With the exception of ultramafic lithologies, rocks of unit ApPsuk3 unit share many common petrographic characteristics. The unit is subdivided into four informal subunits: 1) a subunit of mafic rocks (ApPsuk3a); (2) a subunit of garnet mafic rocks (ApPsuk3b); an anorthosite and quartz anorthosite subunit (ApPsuk3c); and 4) a subunit of ultramafic rocks (ApPsuk3d).
Sukaliuk Complex 3a (ApPsuk3a): Mafic Rocks
Subunit ApPsuk3a is the most represented of mafic rocks of the Sukaliuk Complex. The fine to medium-grained rock is homogeneous, even-grained, granoblastic and appears to have little deformation except near fault zones. Ranging from gabbro to gabbronorite, it is dark grey to greenish in fresh exposure with a peppery and salt alteration patina. Mafic rocks contain 25 to 65% mafic minerals, mainly green to brown hornblende and clinopyroxene with more locally orthopyroxene porphyroblasts. Biotite, in small brown to red flakes, is almost always present, but is only a secondary phase (<5%). Other accessory minerals are opaque minerals (1-5%), quartz (<3%), apatite, zircon, carbonates and phlogopite. Mafic rocks commonly contain a coarse-grained leucocratic diffuse phase (<10%), forming clusters and millimetric to centimetric discontinuous bands within the rock, as well as orthopyroxene porphyroblasts. Centimetric to metric bands of mafic lithologies are generally banded with rocks of the dominant units of the Sukaliuk Complex.
Sukaliuk Complex 3b (ApPsuk3b): Garnet Mafic Rocks
Mafic rocks containing garnet were grouped into subunit ApPsuk3b. Other decimetric to decametric horizons were also observed within the ApPsuk4 metasedimentary unit, but could not be mapped to the scale of our work. Garnet usually accounts for 10 to 25% of the rock and occurs as 3 to 8 mm porphyroblasts. Centimetric to metric horizons and bands with more than 50% garnet are also common. In addition to garnet, the rock contains the same minerals as subunit ApPsuk3a. However, it is generally banded, richer in mafic minerals and looks like a gneiss or amphibolite. The banded texture and spatial association of this subunit with paragneiss of unit ApPsuk4a suggest that this unit is of supracrustal origin.
Sukaliuk Complex 3c (ApPsuk3c): Anorthosite and Quartz Anorthosite
Anorthosite horizons were reported by Verpaelst et al. (2000). This subunit is difficult to distinguish between orthopyroxene intermediate to tonalitic gneiss from unit ApPsuk1, due to identical beige patina and olive-green colour, and is therefore likely under-represented as a result of summer 2017 mapping (Mathieu et al., 2018). Rocks in this subunit have centimetric to decimetric compositional banding. Plagioclase is very fine-grained granoblastic, quartz forms stretched lenses or rods. Mafic minerals (5-10%) are grouped into millimetric, flattened and stretched clusters of orthopyroxene, clinopyroxene, hornblende and red biotite. Accessory phases are sphene, apatite and opaque minerals. This subunit also incorporates minor amounts of granoblastic gabbronorite in centimetric bands.
Sukaliuk Complex 3d (ApPsuk3d): Ultramafic Rocks
Subunit ApPsuk3d consists of foliated dunite, lherzolite, olivine websterite and pyroxenite. The patina is usually light brown with a very dark green to black fresh surface. Rock outcrops as metric to hectometric horizons conformable with other subunits of the Sukaliuk Complex, mostly near metasedimentary rocks of unit ApPsuk4 or interbedded with them. Rocks are composed of varying proportions of olivine, often partially replaced by serpentine and magnetite, orthopyroxene, partially replaced by iddingsite and carbonates, clinopyroxene and actinolite. Accessory phases represent 10 to 15% of the mode and consist of magnetite and spinel (hercynite and picotite). Serpentine is remobilized into millimetric veinlets. Primary textures are in places preserved as horizons with olivine relics (cumulate), although under the microscope minerals are granoblastic and partially replaced.
Unit ApPsuk4 consists of klippes of metasedimentary rocks, mainly migmatitic paragneiss (ApPsuk4a) and minor amounts of quartzite (ApPsuk4b). It is associated with well-defined negative magnetic anomalies on the residual component of the total magnetic field. It is also observed in thiner horizons, interbedded with orthogneiss units of the Sukaliuk Complex.
Sukaliuk Complex 4a (ApPsuk4a): Migmatitic Paragneiss
Paragneiss is variable migmatitized and contains 0 to 30% millimetric to centimetric bands of whitish or brown sugar to greenish mobilisate, depending on whether or not hypersthene is present. Quartz (30-60 modal %) is systematically recrystallized in lenses or rods and has strong undulatory extinction. Stains and thin sections reveal variations in paragneiss and leucosome composition, particularly in the proportion of K-feldspar ranging from 0 to 35% depending on the samples. Decimetric to metric horizons show greater partial melting (banded metatexite and diatexite). Similarly, several thicker horizons of leucosome are observed in paragneiss.
Metasedimentary rocks have a fine granoblastic texture and is well foliated. They contain 2 to 15% millimetric crystals of dark pink garnet (1-4 mm) and 10 to 25% dark brown to red biotite flakes. Bands rich in green hornblende, clinopyroxene and orthopyroxene are also more locally observed; the latter is more common in the leucosome. There is also alternating horizons with and without hypersthene, as well as horizons rich in sillimanite or graphite. The main accessory minerals are opaque minerals, apatite, graphite, zircon, serpentine, chlorite, sphene, allanite, carbonates and rutile. In some areas, particularly in the northern part of the SECP, the ApPsuk4 paragneiss also contains decimetric to metric horizons of clinopyroxene-garnet amphibolite, quartzite, marble and calcosilicate rocks.
Sukaliuk Complex 4b (ApPsuk4b): Quartzite
Quarzite is often impure and forms klippes less than a kilometre wide. It contains more than 75% quartz, feldspars, biotite and muscovite. Accessory minerals observed are apatite, tourmaline, zircon and graphite. Quarzite may also contain sulphides and magnetite. Quartz grains can be indented, lenticular or as bands. Micas locally give the quartzite a lepidoblastic texture, especially obvious in thin section, but which can give the rock a bedded appearance. Quarzite is regularly cut by quartz veins and veinlets.
Unit ApPsuk5 consists of areas characterized by large white intrusive masses, with paragneiss enclaves, interpreted as the result of melting of these metasediments. Similar to the leucosome bands observed in metasedimentary units, these rocks are tonalitic or granitic, in addition to being rich in quartz (30-60%), massive, homogeneous and medium to coarse grained. They contain 2-10% biotite schlierens and 1-5% garnet.
The Sukaliuk Complex forms a N-S strip 20 to 50 km wide followed over 325 km long, representing the western part of the Torngat Orogen. It is limited by the Blumath Deformation Corridor (BDC) to the west and the Lac Pilliamet Lake Shear Zone (LPSZ) to the east. In the northern part of the SECP, the LPSZ (and the Sukaliuk Complex) converges to the Abloviak Shear Zone, which turns WNW in this area.
In general, the ApPsuk1 tonalitic orthogneiss unit represents the dominant facies. The ApPsuk4 paragneiss unit is the second largest and forms sequences up to 10 to 15 km wide by 30 to 70 km long, as well as elliptical-shaped bodies 3 to 4 km wide by 6 to 10 km long. Unit ApPsuk2 is concentrated on the western and eastern borders of the Sukaliuk Complex, where it forms strips of up to 7 km wide and 40 km long. The remaining units cover smaller areas and form lenticular strips, usually less than two kilometres wide within the complex.
Datings made on several tonalitic orthogneiss samples from unit ApPsuk1 have given Archean crystallization ages and Paleoproterozoic metamorphic ages. The spread of Archean ages (3019 to 2716 Ma) indicates the existence of several generations of Archean zircons and reflects the complexity of this unit which contains several phases in diffuse contact.
Dating was also performed on a biotite-garnet-sillimanite diatexite derived from partial melting of an ApPsuk4a paragneiss. The resulting detrital ages range from 2092 to 2690 Ma, indicating that the paragneiss is of Paleoproterozoic age. Paleoproterozoic ages of zircons and monazites allow us to determine the crystallization age of the leucosome between 1812 and 1825 Ma. However, Lu-Hf ages on garnets obtained by Charette (2016) indicate that melting of metasediments had begun earlier, around 1896 Ma.
|Isotopic System||Mineral||Unit||Crystallization Age (Ma)||(+)||(-)||Inherited Age (Ma)||(+)||(-)||Metamorphic Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||ApPsuk1||2897||11||11||–||–||–||1767||55||55||Corrigan et al., 2018 (13IL3157)|
|U-Pb||Zircon||ApPsuk1||2718||8||8||2779||13||13||–||–||–||David et al., personal communication (14BC6224)|
|1844||5||5||Davis et al., 2018 (2013-MP-0057)|
|U-Pb||Monazite||ApPsuk1||–||–||–||–||–||–||1911||8||8||Davis et al., 2018 (2013-MP-0057)|
|U-Pb||Zircon||ApPsuk1a||2659||14||14||–||–||–||1800||50||50||Corrigan et al., 2018 (13SB4161)|
|1801||13||13||Davis et al., 2018 (2013-BC-6150)|
|U-Pb||Monazite||ApPsuk4a||1825||7||7||–||–||–||–||–||–||Davis et al., 2018 (2013-BC-6150)|
The various units of the Sukaliuk Complex are cut by intrusive rocks of the Inuluttalik Suite and often contain decimetric to metric horizons of other units of the Sukaliuk Complex. It was difficult to distinguish the two units in the field given the poor quality of the outcrops visited (large lichen cover) and the similarity between the lithologies. Contact between the two units appears to be diffuse in fresh exposure; however, stains highlight textural differences. The Inuluttalik Suite may represent an evolved phase resulting from partial melting of rocks of the Sukaliuk Complex. This hypothesis is based on the close spatial association between the two units, as well as the presence of numerous biotite schlierens and centimetric to decimetric enclaves of the Sukaliuk Complex within intrusive rocks of the Inuluttalik Suite. The Sukaliuk Complex is in fault contact with the Kangiqsualujjuaq Complex in the west (DBC) and the Lomier Complex in the east (LPSZ).
Does not apply.