The Nuvulialuk Suite was introduced by Verpaelst et al. (2000) in the Koroc River area (sheet 24I) to group bands of mafic and ultramafic intrusive rocks. It was extended southward in the Henrietta Lake area (Lafrance et al., 2015) and northward in the Pointe Le Droit area (Mathieu et al., 2018). This suite only included rocks located west of the Blumath Shear Zone (ZCblm) at that time. As part of a regional synthesis of the southeastern Churchill Province (SEPC; Lafrance et al., 2018), Lafrance and Vanier (2022) reassigned the mafic and ultramafic rocks previously grouped in the Sukaliuk Complex to the Nuvulialuk Suite. This suite thus includes all mafic and ultramafic intrusive rocks of the Falcoz Lithotectonic Domain. These nomenclature changes are detailed in the table below.

Description

Nuvulialuk Suite 1 (pPnuv1): Gabbro, Gabbronorite, Diorite and Norite

Nuvulialuk Suite 2 (pPnuv2): Harzburgite, Lherzolite and Olivine Websterite

In the field, ultramafic rocks of the Nuvulialuk Suite are easily identifiable since they form fairly well-aligned hills, with buff-coloured or orange-brown patina (lichen present) and elephant skin texture caused by the differential erosion of the polygonal joint network on the surface of the rock. In the Koroc River area, ultramafic rocks are generally more severely broken up into sand. Certain magmatic structures are preserved and ultramafic rocks are generally foliated.

Verpaelst et al. (2000) describe four types of ultramafic rocks in unit pPnuv2: dunite, peridotite, pyroxenite and hornblendite. However, the work of Pedreira Pérez (2017) did not demonstrate the presence of dunite. The large-scale intrusions are differentiated and display well-preserved magmatic bedding and primary mineral assemblage. There are different rock phases, gradually moving from cumulate-rich harzburgite and lherzolite at the base to olivine websterite, then gabbro at the top. These rocks are homogeneous and of fine to medium grained. There are magnetite and serpentine veins in positive relief as well as green or brown spinel (hercynite and picotite; <5%), ilmenite (<5%), chromite (<3%) and finely disseminated magnetite (<5%) and sulphides (<5%). These are disseminated as anhedral grains <1 mm. The most commonly observed assemblage is pyrrhotite-pentlandite ± chalcopyrite ± pyrite. Other accessory minerals include phlogopite, apatite and rutile.

The harzburgite is mainly composed of serpentine (40-85%), with or without relics of olivine, orthopyroxene (7-50%), amphiboles (1-15%), clinochlore (1-12%), chromite (1-3%), magnetite and ilmenite (<1%). Orthopyroxene forms aggregates of subhedral to anhedral millimetric grains with undulatory extinction. The lherzolite is essentially composed of the same mineral phases, but in different proportions, with clinopyroxene, orthopyroxene and amphiboles being more abundant between serpentinized olivine crystals. Pyroxenes also form subhedral and anhedral grains up to locally 15 mm. Olivine relics in peridotite are between 1 mm and 2 cm in diameter and are rimmed by serpentine or orthopyroxene. Chromite grains have a zoned appearance due to the presence of hercynite rim. Deformation and metamorphism result in serpentinization and iddingsitization of olivine to varying degrees and formation of tremolite and clinochlore acicular crystals randomly oriented. In rare cases, epidote develops on amphibole and chlorite. Locally, late fractures in the rock contain carbonates, prehnite and epidote. In some thin sections of carbonate rocks associated with ultramafic rocks, there is an abundance of olivine, pyroxene and spinel crystals associated with carbonates. It could represent zones of alteration and metamorphism of listwaenite-type ultramafic rocks. 

The olivine websterite contains mostly pyroxenes, as large crystals or fine granoblastic matrix, and 5 to 25% olivine cumulates variably serpentinized (antigorite and iddingsite). There are also small mottled phlogopite and clinochlore, plagioclase (1-5%), actinolite, magnetite and spinel. During deformation and metamorphism, some of these pyroxenes became granoblastic aggregates of pyroxenes and amphiboles in varying proportions, accompanied by a lesser amount of clinochlore. Spinel appears at the triple points within these aggregates. Even large pyroxene crystals turn into amphibole as spots on or around the grain. In zones of intense deformation, the rock becomes a tremolite-chlorite schist with a nematoblastic texture. Locally, pyroxenes are completely transformed into a mixture of hornblende and actinolite.

The ultramafic rocks are locally completely amphibolitized and transformed into a fine- to coarse-grained, even-grained rock, composed of hornblende, tremolite, actinolite, phlogopite, chlorite and locally some interstitial plagioclase. Amphiboles are granoblastic or form large tangled or lepidoblastic crystals. Serpentinized orthopyroxene relics were observed in some thin sections. The main accessory minerals are opaque minerals (<5%), apatite, magnetite, hercynite, ilmenite, chlorite and sulphides.

Nuvulialuk 2a Suite (pPnuv2a): Dunite, Lherzolite, Olivine Websterite and Pyroxenite

The pPnuv2a subunit groups ultramafic rocks located east of the ZCblm. It is composed of dunite, lherzolite, olivine websterite and pyroxenite, foliated. The patina is generally light brown and the fresh surface is very dark green to black. The rock outcrops as metric to hectometric layers concordant or interstratified with the Lake Harbour Suite supracrustal rocks. The rocks are composed of variable amounts of olivine, partially replaced by serpentine and magnetite, and orthopyroxene, partially replaced by iddingsite and carbonate, clinopyroxene and actinolite. Accessory phases account for 10-15% of the mode and are magnetite and spinel (hercynite and picotite). Serpentine is remobilized in millimetric veinlets. Primary structures are locally preserved as layers with olivine relics (cumulate), even though the minerals are granoblastic and partially replaced under the microscope.

Nuvulialuk 3 Suite (pPnuv3): Banded Anorthosite

Layers of anorthositic composition have been reported by Verpaelst et al. (2000). This subunit is difficult to distinguish from the tonalitic to intermediate orthopyroxene gneiss of the Sukaliuk Complex due to the identical beige patina and olive-green hue; therefore, it is likely underrepresented following the mapping work of Mathieu et al. (2018). Rocks in this subunit exhibit centimetre- to decimetre-sized compositional banding. Plagioclase is very fine to fine grained and granoblastic. Quartz forms stretched lenses or rods. Ferromagnesian minerals (5 to 10%) are grouped in millimetric, flattened and stretched clusters composed of orthopyroxene, clinopyroxene, hornblende and red biotite. The accessory phases are sphene, apatite and opaque minerals. This subunit also includes a small amount of granoblastic gabbronorite in centimetric bands.

Thickness and Distribution

Rocks of the Nuvulialuk Suite typically are <1 km wide by 1-5 km long. The largest intrusions are in the areas of Mount Nuvulialuk (sheet 24I06) and Ijurvik Lake (sheet 24I03) where they are 2-3 km wide and nearly 20 km long. The Nuvulialuk Suite covers a limited area of ~360 km² and is uniformly distributed within the Falcoz Lithotectonic Domain. Rocks of the pPnuv1, pPnuv1a, and pPnuv1b units and subunits are the dominant lithologies, covering ~104 km², ~114 km², and ~86 km² respectively. The pPnuv2, pPnuv2a, and pPnuv3 units and subunits cover smaller areas, ~42 km², ~10 km², and ~4 km² respectively.

Dating

The age of ~1863 Ma was obtained in a decametric layer of amphibolite within a tonalitic orthogneiss of the Kangiqsualujjuaq Complex. The amphibolite is foliated and displays a lower degree of deformation than the gneiss with which it is intestratified. Verpaelst et al. (2000) interpret this amphibolite layer as a dyke of the Nuvulialuk Suite that was probably tectonically juxtaposed to the gneiss during the Paleoproterozoic deformation episode. The Archean age is interpreted as an inherited age of zircons that underwent remobilization during Trans-Hudsonian metamorphism.

The Geological Survey of Canada has dated the emplacement of a mafic intrusion associated with the Nuvulialuk Suite at ~1840 Ma. The sample was taken from the NE portion of sheet 24H10. 

Charette et al. (2021) interpret a crystallization age of a garnet gneissic gabbronorite of the Nuvulialuk Suite around 1856 Ma (oldest zircon population). The sample analyzed was from an outcrop that was reassigned to the Nuvulialuk Suite by Lafrance and Vanier (2022). Charette et al. (2021) also dated the regression to the solidus phase at ~1817 Ma from the younger zircon population. Finally, Lu-Hf and Sm-Nd geochronological studies on garnets by these authors allowed them to interpret respectively the minimum crystallization age of this mineral (~1839 Ma) and the cooling age at the amphibolite facies (~1806 Ma).

Stratigraphic Relationship(s)

Ultramafic and mafic intrusive rocks of the Nuvulialuk Suite are commonly spatially associated with metasedimentary rocks of the Lake Harbour Suite. The contacts with the paragneiss and quartzite are marked by significant alteration indicating fluid circulation. Verpaelst et al. (2000) interpret these intrusive rocks as sills and dykes a few kilometres long that have developed within the Lake Harbour Suite volcano-sedimentary sequences. They also form imbricate layers within Archean gneissic complexes.

The work of Pedreira Pérez (2017) suggests that some of the intrusions assigned to the Nuvulialuk Suite, located near the ZCblm, correspond to an ophiolitic sequence. However, the work of Charette (2016) indicates that metasedimentary rocks from the area began to melt as of 1885 Ma (start of compressive regime and burial). The emplacement ages of 1840 Ma and 1863 Ma obtained in the Nuvulialuk Suite therefore seems to exclude the possibility that it is an ophiolite but rather differentiated intrusions. 

Paleontology

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References

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