Background and Methodology

The Koksoak Shear Zone (ZCkok) was introduced as part of the Southeastern Churchill Province synthesis. No regional shear zone had previously been identified in this area. However, aeromagnetic maps had prompted some authors to extend the Lac Tudor Shear Zone in a NNW direction to join the Lac Turcotte Fault (Wardle et al., 2002; Corrigan et al., 2018). This record is based on a compilation of structural measurements and on the interpretation of aeromagnetic maps (D’Amours and Intissar, 2012) of the northern part of the Baleine Lithotectonic Domain.

Boundaries and Morphology

Stratigraphic Units Concerned

Stratigraphic units affected by the ZCkok are the Qurlutuq and Ungava complexes, as well as the False Suite.

Structural Characteristics

❯ Main Fabrics

The compilation of structural measurements allows defining an average foliation plane oriented at 117°/85°. A certain variability of the data is observed, but in general, foliations are strong and have a dip >60°. A very limited number of mineral and stretch lineation measurements are available for this shear zone. Three measurements suggest that the dominant linear fabric is subhorizontal and oriented NW-SE.

❯ Other Fabrics

Not observed.

❯ Folds

Does not apply.

❯ Crosscutting Relationships

Not observed.

❯ Kinematics

No observations were made in the field to determine the kinematics of this shear zone; however, assuming that this zone is an extension of the Rivière George Shear Zone (ZCrge), a dextral movement is interpreted.

Deformation Style

The intensity of deformation in the ZCkok varies from moderate to intense. Most outcrops display a regular planar fabric, such as foliation or gneissosity. The more deformed sites are affected by a mylonitic fabric. Although it is difficult to define a deformation style from geological compilation and aeromagnetic data, it appears that the deformation style of the ZCkok is parallel. Indeed, aeromagnetic lineaments associated with this structure are parallel to each other and projected fabrics have a constant orientation.

Metamorphic Characteristics

Rocks of the Baleine Lithotectonic Domain were affected by a partial melting event in the Archean and by amphibolite facies metamorphism in the Paleoproterozoic (Lafrance et al., 2020). Structures observed in the ZCkok area are probably Paleoproterozoic in age (Simard et al., 2013). The ZCkok is therefore believed to have developed at the amphibolite facies.

Alterations

Not observed.

Geophysical Characteristics

The aeromagnetic signature of the ZCkok is defined by a strip of continuous and parallel lineaments. Within this strip, rocks are generally more deformed than outside. The lineaments are cut by units of the De Pas Supersuite characterized by barely deformed rocks.

Chronological Markers

The ZCkok is cut by the De Pas Supersuite, which intruded between  1865 Ma and 1805 Ma. This structure is therefore probably contemporaneous with the ZCrge, whose minimum age of deformation is 1812 Ma (Vanier, 2019). Furthermore, by extrapolating the ZCkok to the SSE in the De Pas Supersuite, it approximately joins the ZCrge.

References

Publications Available Through Sigéom Examine

Other Publications

Suggested Citation

Contributors