Background

Description

Inuluttalik Suite 1 (nApPina1): Enderbite

Inuluttalik Suite 2 (nApPina2): Charnockite and Opdalite

In addition to forming kilometric intrusive masses, rocks of unit nApPina2 also occur as millimetric to decimetric intrusions, pink or brown sugar in the pPina1 enderbite and in orthogneisses of the Sukaliuk Complex. In outcrop, the rock is easily confused with the brown sugar-coloured phases of the nApPina1 enderbite. However, it contains 20 to 45% K-feldspar, which is generally not twinned in thin section. Charnockite commonly shows an unequal distribution of minerals that tend to form monomineralic centimetric clusters. It contains 20 to 25% quartz with strong undulatory extinction. Ferromagnesian minerals (8-20%) consist of brown to red biotite, orthopyroxene and hornblende with local clinopyroxene. Orthopyroxene is replaced to varying degrees by hornblende or iddingsite. The rock is partially recrystallized along grain edges. The main accessory minerals are opaque minerals, apatite, zircon, sphene, epidote and allanite. 

Inuluttalik Suite 2a (nApPina2a): Granite and Granodiorite

Like the nApPina1 enderbite unit, charnockite and opdalite are locally retrograded to the amphibolite facies. These intrusive rocks are homogeneous, medium grained and light to medium pink. They are foliated and show lineations, locally protomylonitic on the edge of shear zones. The main expression of deformation is the alignment of ferromagnesian minerals (5-12%) consisting of brown biotite and muscovite flakes. Smoky quartz (20-27%) forms large zones with undulatory extinction, lenticular in places. Plagioclase and microcline (15-50%) show partial recrystallization between grains. Subunit nApPina2a contains the same accessory minerals as unit nApPina2. 

Inuluttalik Suite 3 (nApPina3): Pegmatitic Granite and Charnockite

The majority of the outcrops locally consist of pegmatitic intrusive rocks that cut all the units of the Inuluttalik Suite. The rock is dark pink, leucocratic, massive or marked by the lineation. It contains between 2 and 5% ferromagnesian minerals (biotite ± hornblende ± hypersthene), ~25% quartz and a lesser amount of muscovite and magnetite.

Thickness and Distribution

The Inuluttalik Suite forms elongated plutons parallel to the regional structural grain that intrude the orthogneisses of the Sukaliuk Complex and are located in the eastern part of the Falcoz Lithotectonic Domain. It covers a total area of ~2121 km². The rocks of the nApPina1 (~1299 km²), nApPina1a (~386 km²) and nApPina2 (~325 km²) units and subunits form hectometric to decakilometric wide intrusions ranging in length from 1 km to nearly 100 km. The nApPina2a (~22 km²) and nApPina3 (~2 km²) units and subunits are much more constrained and have only been described in the Pointe Le Droit area (Mathieu et al., 2018).

Dating

Samples from outcrops 2013-DB-1000, 2014-IL-3108, 2013-BC-6179, and 2013-CB-5168 were isotopically dated. The abundance of Archean inherited ages, primarily between 2.8 Ga and 2.5 Ga, reflects the complexity of this suite and suggests a mixture between Archean and Paleoproterozoic components (Corrigan et al., 2018; Davis et al., 2018).

Paleoproterozoic ages between ~1864 Ma and ~1822 Ma correspond to metamorphism related to the Torngat Orogeny, which was maintained at the granulite facies over an extended period (1885-1810 Ma; Charette, 2016; Charette et al., 2021). Assuming that the Inuluttalik Suite is a product of partial melting of the Sukaliuk Complex orthogneisses, these ages could represent those of the crystallization of anatexis magmas.

With respect to the Neoarchean component, also recognized locally in the Sukaliuk Complex, it is difficult to determine whether it reflects the emplacement of a Neoarchean crust, as interpreted by Corrigan et al. (2018), or a period of remobilization of an older (~2.9 Ga to ~2.7 Ga) Neoarchean crust. Thus, there may have been more than one episode of migmatization. The younger metamorphic ages (1808 Ma and 1800 Ma) could be explained by the slow cooling episode related to exhumation estimated between 1810 Ma and 1730 Ma by Charette et al. (2021).

Stratigraphic Relationship(s)

The Inuluttalik Suite includes hypersthene felsic intrusive rocks that could represent evolved products of partial melting of orthogneisses of the Sukaliuk Complex (Lafrance et al., 2015; David, 2019). In fact, the rocks of the Inuluttalik Suite contain numerous orthogneiss enclaves, which could constitute rafts within a diatexite. In outcrop, the distinction between these two units is generally difficult due to the poor quality of the outcrops (lichen cover) and the great similarity between lithologies. The contact between the two units seems diffuse on a fresh surface. However, rock staining makes it possible to highlight the structural differences.

Charette (2016) mentioned that the lack of texture indicating partial melting in the Sukaliuk Complex could be linked to their destruction during high temperature deformation. The presence of coarse-grained leucocratic bands in gneiss, the close spatial association between the two units, and the presence of numerous biotite schlieren inside the intrusive rocks of the Inuluttalik Suite indicate that the Torngat orogenesis could represent a migmatization episode associated with the extraction and accumulation of anatectic liquids. 

Paleontology

Does not apply.

References

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