The Nanuk Complex was introduced in the Sirmiq Lake area (Vanier and Lafrance, 2020) in order to group felsic to intermediate gneissic or migmatitic rocks, of gneissic or migmatitic appearance, of the Kovik Lithotectonic Domain.It was extended southwards in the Lake Amarurtuup regionarea (Lafrance et al., 2023), and eastwards in the Deception Bay regionarea (Vanier and Bilodeau, 2024).It includes the gneissic or banded potassic intrusive rocks previously assigned to the Arviq Suite, in the Lake Sirmiq regionarea (Vanier and Lafrance, 2020), as well as those assigned to the ApPkvk4, ApPkvk5 and ApPkvk6 units of the Kovik Complex, in the Cape Wolstenholme regionarea (Charette and Beaudette, 2018).

Tonalite and quartz diorite contain 158-287% quartz, <75% K-feldspar and 7-125% ferromagnesian minerals. Brown to greenBbiotite is always in greater proportion than green hornblende, the latter may even be locally absent. Microcline forms is disseminated in fine interstitial crystals and these are more numerous in leucosome bands. In thin section, the general fabric is partially granoblastic to interlobed. Quartz forms large elongated crystals with undulatory extinction. Biotite is lepidoblastic and slightly chloritized. Epidote, sphene, opaque minerals, apatite, muscovite, monazite, allanite, carbonate and zircon are the accessory phases.Plagioclase is slightly sericitized.

Nanuk Complex 1a (ApPnuk1a): Homogeneous Tonalite and Quartz DioriteBiotite ± hornblende tonalite, quartz diorite bands, <20% granite injections, mafic enclaves

Although it is the main unit on some outcrops, subunit Anuk1a is generally represented by decimetric to decametric layers within unit Anuk1 in the Lake Amarurtuup area (Lafrance et al., 2023).It can be distinguished from the Anuk1 unit by a well-defined rectilinear banding, consisting of alternating milimetric to centimetric bands of grey tonalite, white tonalite and dark grey quartz diorite. These lithologies are all fine-grained, equigranular and partially granoblastic.

This orthogneiss subunit represents the dominant lithological sequence of the Nanuk Complex in the Deception Bay area.It is composed of banded biotite-hornblende tonalite.The percentage of bands varies greatly within this unit.They are mainly intermediate in composition.This unit also contains up to 20% of granitic injections parallel to subparallel to the foliation.Mafic enclaves are distributed heterogeneously in the unit, varying in proportion from 0 to 20% depending on the sector. These enclaves are transposed in the foliation.

The main minerals occurring in tonalite are quartz (20-40%) and plagioclase (40-70%).Microcline is generally not found in the unit, aside from a few areas where the percentage varies from 3 to 10%.Biotite is the most commonly observed secondary mineral, with its proportion varying from 3 to 15% depending on the sample. Biotite defines the characteristic lepidoblastic structure systematically observed in the unit.Fine subhedral hornblende (1-3%) is found in the interstices of plagioclase and quartz crystals.Accessory minerals are apatite and sphene, and to in lesser proportion epidote, allanite, opaque minerals, and finally muscovite and zircon.

Some alteration is noted in several samples, particularly with the presence of muscovite and sericite, interpreted as products of alteration of plagioclase. In the altered samples, the latter are beige with a milky appearance. Chlorite replaces biotite in several samples.

Fieldspar and quartz take the form of heterogranular and interlobed crystals. The grain size varies greatly, particularly in the case of quartz, which can be elongated and amoeboid, indicating grain boundary migration. The preferential axis of elongation is parallel to the one defined by the alignment of biotite. These quartz grains form pinch microstructures with biotite, which is commonly found in several samples

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In addition to forming decimetric layers in unit ApPnuk1, subunit ApPnuk1a may represent the dominant lithology of some outcrops. This tonalite or quartz diorite represents areas where the rock is more homogeneous and free of banding. The rock is even grained, fine grained, foliated and medium-light grey. It contains ~20% quartz and 15% ferromagnesian minerals, which are dominated by biotite, but also includes 2-3% hornblende. Microscopic observations are similar to those of unit ApPnuk1. Retrograde muscovite and carbonates are also incidentally present.

Nanuk Complex 223 (ApPnuk232): Biotite ± Magnetite Banded, Porphyroid or Speckled Granodiorite and Biotite Schlierens

 In outcrop, unit Anuk2 can be difficult to distinguish from unit Anuk1. It can be distinguished by a slightly lighter colour and the scarcity of hornblende, but above all by the common presence of a coarse-grained pink granite facies injected into granodiorite or monzogranite. These injections are visible in the form of millimetric to centimetric bands subparallel to the foliation or intersecting at a slight angle. Granodiorite and monzogranite are equigranular and medium to fine grained. These rocks also contain up to 15% whitish to pinkish leucosome and decimetric dioritic layers.

Anuk2 rocks contain 20-30% quartz, 25-35% K-feldspar and 5-15% ferromagnesian minerals. The latter are dominated by biotite, while hornblende is rarely present. Under the microscope, the general fabric is partially granoblastic to interlobed. K-feldspar consists mainly of microcline and myrmekites are common. Quartz exhibits undulatory extinction and is observed locally as subgrains. Biotite is lepidoblastic and partially chloritized. Accessory minerals include epidote, apatite, allanite, opaque minerals, sphene and zircon.

 In the Deception Bay area, this subunit consists mainly of banded granodiorite with a gneissic appearance and a light grey colour. Main minerals are in highly variable proportions due to the uneven percentage of bands. Its generally more potassic composition, the fine to coarse grain size and the presence of smoky quartz are characteristics that distinguish it from the main unit Anuk1. Granodiorite contains beige to pinkish feldspar bands, typically low in quartz and ferromagnesian minerals. These bands are interpreted as the result of a mineral segregation of metamorphic origin.

 Rocks are composed of 25-40% quartz, 10-50% plagioclase, 5-50% microcline and 5-10% orthoclase, depending on the sample. Recrystallized microcline phenocrysts occur in isolation, accompanied by clusters of very fine-grained microcline in the pressure shadows of these phenocrysts. Feldspars are generally damouritized and locally perthitic. Myrmekites are observed in some samples. Ferromagnesian minerals include biotite (3-7%) and hornblende (0-1%). The distribution of biotite schlieren also varies within the unit. Like the bands, schlierens define the gneissosity of the rock. The biotite they contain appears to predate the main fabric. This biotite is partially replaced by chlorite in some samples. Accessory minerals include magnetite, apatite and muscovite, which account for no more than 1% of the rock. Other minerals observed locally are sphene, epidote, allanite and zircon. Under the microscope, minerals appear to be highly recrystallized, as evidenced by their highly complex amoeboid morphology and wide range of grain sizes. Quartz forms pinch figures with biotite in schlieren-bearing zones, and clusters of subgrains form chessboards in some samples.

Nanuk Complex 2a (Anuk2a): Granitic orthogneiss

 Like the Anuk1a subunit, the Anuk2b orthogneiss, characterized by rectilinear banding, forms decimetric to decametric layers within the unit Anuk2. The composition of the bands, which alternate from millimetric to centimetric, is granitic and locally granodioritic. The bands are either grey, pink or white. The rocks are equigranular and fine grained.

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Migmatite of unit ApPnuk2 is stromatic or containing schlierens, and quartzodioritic, tonalitic or dioritic in composition. It comprises mostly biotite zones in diffuse contact with hornblende zones. This migmatite is interpreted by Vanier and Lafrance (2020) as being derived from partial melting of tonalite and quartz diorite of unit ApPnuk1. Foliation is very undulating and the melting percentage varies greatly. Ferromagnesian minerals either form clusters faintly aligned in foliation or schlierens. The fabric is heterogranular, and quartz is amoeboid and forms subgrains. The same accessory minerals as in unit ApPnuk1 are observed.

Nanuk Complex 32 (Anuk32): MMigmatitic rRocks

In some areas, rocks from the Anuk1 and Anuk2 units have undergone significant partial melting. They have therefore been assigned to the Anuk3 unit. It should be noted that the transition between these units is generally gradual and that the boundary between them is arbitrary. The degree of melting varies greatly.

In thin sections, the grains have a serial distribution and an interlobed shape. Quartz is amoeboid with undulatory extinction and forms subgrains. Ferromagnesian minerals (10-20%) consist of similar proportions of brown to green biotite and green hornblende. Hornblende is locally replaced by a mixture of chlorite-epidote-carbonate. Biotite is variably chloritized and locally intergrown with quartz. Plagioclase is slightly sericitized and in places contains muscovite inclusions in sheets. Epidote, apatite, allanite, zircon, sphene and opaque minerals are present in minor proportions.

Nanuk Complex 3a (Anuk3a): Stromatic metatexite

 The Anuk3a metatexite is stromatic. The leucosome is generally whitish and medium to coarse grained. It forms centimetric undulatory bands that are commonly folded. Its composition varies from tonalitic to granodioritic or granitic. The palaeosome is similar to that of the Anuk1 and Anuk2 units. At the edge of the leucosome, the ferromagnesian minerals are coarser. These commonly form millimetric to centimetric clusters.

Nanuk Complex 3b (Anuk3b): Schlieren diatexite

 Many areas contain an even higher proportion of leucosome. These migmatites have a heterogeneous appearance and contain a high proportion of whitish anatectic granite. In outcrops where banding is present, it is rather chaotic. Raft structures and schlieren are common. The rafts are generally decimetric to metric and their composition is similar to that of the Anuk1 and Anuk2 units. Ferromagnesian minerals (hornblende and biotite) are concentrated in schlieren that weakly mark the foliation.

Nanuk Complex 3c (Anuk3c): Clusters of leucosome diatexite

 In Anuk3c migmatites, leucosome occurs in centimetric clusters (patchy migmatite). These clusters are slightly coarser than the surrounding rock with which they are in diffuse contact. This texture is difficult to distinguish in outcrop, and the rocks of unit Anuk3c can be easily confused with the homogeneous tonalite and quartz diorite of the Uvikkaq Suite.

Nanuk Complex 4 (Anuk4): Amphibolitized Gabbro and Gabbronorite, Locally Containing Garnet or Biotite

This subunit comprises enclaves and boudins of mafic intrusive rocks mappable within the gneissic units of the Nanuk Complex (Anuk1a, 1b, 1c and 2), in the Deception Bay area (Vanier and Bilodeau, 2024). These geological bodies have been observed in several outcrops, but given their relatively modest size, they rarely appear on regional-scale geological maps. Mappable features form isolated megaboudins or multi-decametric rafts, enveloped by the gneissosity of surrounding rocks. The rocks have the same composition as metamorphosed gabbro and gabbronorite. They are brown to dark grey-green in fresh fracture and greenish-beige or greenish-brown to blackish in alteration patina. Rock composition varies widely, with hornblende and plagioclase dominating the mineralogy, followed locally by garnet, clinopyroxene and orthopyroxene. Mineral proportions generally vary significantly. In general, mineral proportions vary markedly. The rock is granoblastic, generally equigranular and medium grained. No crosscutting relationships have been reported between the different facies. The rocks are not magnetic.

Nanuk Complex 5 (Anuk5): Banded and Migmatized Amphibolite, Paragneiss, Minor Proportion of Quartzite and Calc-silicate Rock.

Unit Anuk5 is made up of amphibolite and paragneiss klippes found in units Anuk1a, 1b and 2.

Nanuk Complex 5a (Anuk5a): banded and migmatized amphibolite, layers of migmatized garnet ± sillimanite paragneiss

A few layers of amphibolitized and partially migmatized mafic metavolcanic rocks have been identified on the coast of the Hudson Strait, in the Deception Bay area (Vanier and Bilodeau, 2024). These rocks are strongly deformed. They form tabular bodies that match the gneissosity of surrounding lithologies. They are black to very dark green in fresh fracture and green and white to very dark green in alteration patina. These rocks are mainly composed of hornblende and plagioclase. They also contain variable percentages of coronitic garnet and clinopyroxene, in addition to biotite, quartz and opaque minerals in accessory proportions. Amphibolite has a fine to medium grain size and is characterized by a banded appearance, which is evidenced by variations in composition, colour and grain size. A small percentage of mobilisate, a product of partial melting of the unit, is present in outcrops of this subunit. The mobilisate consists of small feldspathic clusters exhibiting a stromatic structure. The amphibolite contains small layers of slightly migmatitic grey-brown biotite-garnet-sillimanite paragneiss.

Nanuk Complex 5b (Anuk5b): Biotite ± garnet ± sillimanite ± kyanite ± cordierite paragneiss, minor proportion of quartzite and calc-silicate rock

This subunit brings together the mappable klippes of metasedimentary rocks identified within the gneissic units of the Nanuk Complex, in the Deception Bay area (Vanier and Bilodeau, 2024). These rocks form tabular and folded bodies up to 150 m thick. They have been observed in several outcrops, but given their relatively small size, they rarely appear on regional-scale geological maps. The main lithology of this unit consists of a biotite paragneiss and, secondarily, various aluminosilicates such as garnet, sillimanite, kyanite and cordierite.

Thickness and Distribution

The Nanuk Complex is one of the main units of the Kovik Lithotectonic Domain. It mainly forms an elongated structure >145 km long and 30 km wide to the south of the Sugluk Shear Zone (sheets 35F13 to 35F16). It also forms bands a few hundred metres to a few kilometres wide oriented NE-SW to NW-SE outside this elongated structure. Its eastward extension has been defined to the western shore of Deception Bay and extends under the waters of the Hudson Strait to the north (Vanier and Bilodeau, 2024). The size and thickness of the subunits are difficult to assess. Klippes of amphibolite and paragneiss attributed to the Nanuk Complex (Anuk5) form bodies that are interpreted as enclaves of highly variable dimensions, the majority of which cannot be mapped at the scale used in the region.

The Nanuk Complex is currently limited to the southern part of the Sirmiq Lake area (Vanier and Lafrance, 2020), in the Kovik Lithotectonic Domain.

Dating

None.Archean ages obtained from samples collected from outcrops 2021-IL-2132 and 2021-IL-3106 are interpreted by Davis (2023) as indicating the location of an Archean pluton, around 2700 Ma, derived from a basement with an age of ~2800 Ma. Ages around 2700 Ma could also be associated with an episode of Archean metamorphism (Lafrance et al., 2023) that affected rocks emplaced between 2831 Ma and 2770 Ma.