The Sainte-Hélène Complex was introduced by Charette and Beaudette (2018) to distinguish gneissic and migmatitic, orthopyroxene-free tonalite to diorite lithologies of the Narsajuaq Lithotectonic Domain. It was recently extended eastward in the Sirmiq Lake area (Vanier and Lafrance, 2020). Previously, these lithologies were mostly included in unit pPNAR1 of the older suite and, in a smaller proportion, in unit pPNAR2 of the younger suite described by St-Onge and Lucas (1992) and St-Onge et al. (1992).

Based on geochronological data, the units formerly grouped in the Sainte-Hélène Complex by Charette and Beaudette (2018) and located north of the Naujat Shear Zone were reassigned to the Uummanaq Suite (Vanier and Lafrance, 2020).

The name of the unit refers to Pointe de Sainte-Hélène (NTS sheet 35L01).

The Sainte-Hélène Complex groups foliated to gneissic rocks metamorphosed at the amphibolite facies located north of the Sugluk Shear Zone, whose composition varies from tonalitic to dioritic. In addition to the compositional variations that mark gneissosity within this complex, many injections and bands conformable with foliation produce a banded appearance. Locally, isoclinal folds with an axis parallel to the foliation affect the gneissosity and felsic bands. Open folds of metric amplitude, folding the entire banded gneissic sequence, were also observed, particularly near the coast SW of Ivujivik.

The two main lithologies in this group were divided according to the dominant composition observed in outcrop, namely, migmatized quartz diorite (pPshn1) and migmatized tonalite (pPshn2). These two units are commonly observed in transitional contact or as imbricate layers. The diatexite unit (Ashn3) is interpreted by Charette and Beaudette (2018) as resulting from melting of quartz diorite and tonalite since diatexite forms zones within the latter. Finally, unit Ashn4 consists of quartz diorite and quartz monzodiorite. 

Quartz diorite is dark grey, foliated, fine to medium grained and gneissic. Gneissosity is produced by a transitional or sharp variation in the amount of ferromagnesian minerals (15-30%) and quartz (5-17%). Thus, there is alternating centimetric to decimetric bands and layers of dark-grey hornblende-biotite diorite, grey biotite ± hornblende quartz diorite and light-grey biotite quartz diorite. In some parts of the Cape Wolstenholme area (Charette and Beaudette, 2018), quartz diorite displays little compositional variation (non-gneissic), but commonly includes diffuse and lenticular leucosomes as well as small (0.5-1 cm) plagioclase crystals. Quartz diorite has characteristic banding marked by two types of bands.

First, leucocratic bands make up 15-20% of lithology; they are interpreted as leucosome. These bands are millimetric to centimetric and have the same grain size (or are slightly coarser grained) as quartz diorite, with which they are in sharp contact. Their composition is tonalitic, but may include a small amount of K feldspar locally, which then corresponds to a granodiorite. Leucosomes are locally folded or discontinuous and generally conformable to gneissosity. In places, they become coarser and cut the planar fabric. It is possible to observe in places that these conformable and cross-cutting bands produce a typical metatexite mesh texture. Lenticular clusters of clinopyroxene and hornblende are also observed and could be melanosome. Locally, orthopyroxene occurs as relic in the core of hornblende. In less migmatized zones, the leucosome forms slightly coarser-grained centimetric clusters.

Second, diorite, monzodiorite or gabbro bands or layers richer in ferromagnesian minerals (25-50%)  also occur in quartz diorite. Making up 5-15% of outcrops, these are in sharp contact with quartz diorite, and, in places, boudinaged. They are centimetric to decametric and are conformable to foliation. These mafic layers are even grained, medium-grained and can easily be confused with the hypersthene-free gabbro and diorite unit of the Pingasualuit Complex (nApgs1a). However, they are distinguished by the presence of biotite, in similar amounts to hornblende, and the absence of pyroxene.

In thin sections, the fabric is mostly not even grained and interlobed to amoeboid. Plagioclase can be locally granoblastic and ferromagnesian minerals mark foliation. Hornblende is the main ferromagnesian mineral, closely followed by biotite, which has a reddish colour in some thin sections. The latter, in addition to occurring as flakes, also replaces hornblende. Chloritization of biotite is observed in some bands. Quartz has undulatory exticntion and commonly forms thin lenses. Partially uralitized clinopyroxene is oberved locally. Observed accessory minerals are, in order of importance, sphene, apatite, opaque minerals, zircon, epidote, carbonate and chlorite (altering biotite).

Complexe de Sainte-Hélène Complex 1a (Ashn1a): Mylonitized Heterogeneous Diorite

Subunit Ashn1a groups heterogeneous outcrops forming an E-W strip located in the northern part of sheet 35K01. Rocks of this subunit are mostly protomylonitic, but less deformed areas have also been identified. The deformed rock displays sharp or diffuse alternation of centimetric to decimetric layers of diorite, quartz diorite, tonalite and amphibolitized gabbro in varying proportions, giving a tectonic gneiss appearance to the rock. There are also millimetric to centimetric hornblende ± clinopyroxene porphyroclastic leucocratic bands. These could represent leucosome highly transposed by deformation. Bands have a quartz diorite, locally quartz monzodiorite composition. Quartz forms milimetric bands and plagioclase locally forms millimetric to centimetric porphyroclasts. Some metric layers also contain millimetric to centimetric garnet porphyroclasts.

In less deformed areas, the main lithology is granular tonalite containing numerous decimetric to metric diorite and quartz diorite boudins. Tonalite is usually massive in appearance, but contains schlierens or elongated clusters of ferromagnesian minerals similar to those observed in diorite and quartz diorite, that is, predominantly hornblende with lower amounts of biotite.