Background and Methodology

This record is based on aeromagnetic maps’ interpretation (Intissar et al., 2014) and information gathered from geological survey conducted in the summer of 2019 in the Sirmiq Lake area (Vanier and Lafrance, 2020).

Boundaries and Morphology

Stratigraphic Units Concerned

The main stratigraphic units present in the DSaku are the Pingasualuit, Sainte-Hélène and Estre complexes. The Crony and Gastrin suites are also present in lesser proportions and are concentrated in the southern part of the domain.

Structural Characteristics

❯ Main Fabrics

The dominant fabric in the DSaku is a tectometamorphic foliation oriented WSW dipping of 45° northward on average. This planar fabric is penetrative and features a stretching lineation slightly offset westward from the average regional foliation’s slope line. The foliation is marked by the alignment of biotite flakes and by mineral segregation in millimetre-thick bands, which gives a more or less gneissic appearance to the rock, particularly within the Sainte-Hélène Complex. Discontinuous quartz bands a few millimetres wide are also present in the richest quartz lithologies. As for the linear fabric, it is expressed by the stretching of quartz in intermediate and felsic rocks and by the elongation of ferromagnesian mineral clusters in mafic protoliths.

❯ Other Fabrics

Not observed.

❯ Folds

Does not apply.

❯ Crosscutting Relationships

None.

❯ Kinematics

Not observed.

Deformation Style

The intensity of deformation in the DSaku is moderate to intense. All outcrops have a clearly defined foliation that can be correlated with surrounding outcrops. The same applies to lineations that are regularly present. Mylonites are not widespread in the DSaku, but several outcrops dispaly strong anisotropy which is marked by the stretching of quartz, feldspar or ferromagnesian mineral clusters. The deformation style attributed to the DSaku is parallel, since fabrics observed are regular and parallel to each other at the scale of the domain.

Metamorphic Characteristics

The metamorphic peak in the DSaku is assessed at the granulite or amphibolite facies, depending on the area (Vanier and Lafrance, 2020). Indeed, like the Crony Suite, the Sainte-Hélène Complex is mostly free of orthopyroxene. Like other structural domains of the Narsajuaq Lithotectonic Domain, the presence of stromatic banding parallel to the tectometamorphic foliation supports the view that partial melting is synchronous with the main deformation. Thus, the metamorphic facies associated with the main deformation is the upper amphibolite to granulite facies.

Alterations

Does not apply.

Geophysical Characteristics

On the residual magnetic field map, the DSaku corresponds almost exclusively to a positive magnetic anomaly which is particularly marked for the Estre and Pingasualuit complexes. This positive anomaly is elongated parallel to the regional structural grain and has low amplitude magnetic peaks. These are also parallel to regional foliation and were used to draw foliation traces.

Chronological Markers

There is no geochronological analysis available in the DSaku. It is assumed that the main deformation occurred at the same period as in surrounding structural domains, where it may have occurred in conjunction with regional metamorphism. The latter is constrained to ~1806 ±38 Ma (Navvaataaq Suite), 1880 ±2 Ma and 1841 ±2 Ma (Pingasualuit Complex; Davis and Sutcliffe, 2018).

References

Publications Available Through Sigéom Examine

Suggested Citation

Contributors