Background

Description

Suluraaq Suite 1 (pPslq1): Speckled Quartz Monzodiorite and Monzodiorite

Lithologies of unit pPslq1 display a mineralogical variation from monzodiorite to quartz monzodiorite, as well as a characteristic speckled texture. Banding is produced by compositional variations as well as the heterogeneous distribution of K-feldspar. The latter are concentrated in diffuse, discontinuous, leucocratic and coarser-grained bands. Compositional variations are defined by the content of ferromagnesian minerals that fluctuate between 20% and 30%. Millimetric plagioclase clusters give a speckled appearance to the rock, while centimetric leucocratic bands, interpreted as leucosomes, mark migmatitic banding. These leucosomes make up between 10% and 15% of outcrops. They are granitic, conformable to foliation and in sharp to diffuse contact. Generally, the appearance of this unit is homogeneous, but may have different facies marked by a change in grain size, from fine to medium. Centimetric to decimetric (2-50 cm) layers or boudins of ultramafic composition containing clinopyroxene, hornblende and magnetite are in diffuse or transitional contact and are observed in varying proportions on the outcrop.

Suluraaq Suite 2 (pPslq2): Banded and Mylonitized K-feldspar Porphyroclastic Quartz Monzonite

Unlike subunit pPslq1a, quartz monzonite of the Suluraaq Suite (pPslq2) is mylonitized and banding is marked by porphyroclastic bands separated by thin layers of ferromagnesian minerals. The latter are associated with discontinuous felsic bands marking banding. Lithology can in places be almost exclusively made up of bands, but when they are smaller in proportion, they typically account for 15-25% of the lithology. Millimetric to centimetric (0.5-2 cm) polycrystalline porphyroclasts are formed of recrystallized plagioclase and K-feldspar. Quartz forms thin millimetric bands. Ferromagnesian minerals occur as millimetric blades forming an anastomosed network between porphyroclastic bands. Biotite is the most abundant ferromagnesian mineral, and forms elongated clusters in foliation. Apatite is also present in these clusters (5-10%). This unit is rich in K-feldspar and geochemical analyses reveal a higher K₂O content than in unit pPslq1 (~5 wt.%).

Thickness and Distribution

Speckled monzodiorite (pPslq1) and porphyraceous quartz monzonite (pPslq1a) are located within and north of the Sugluk Suture. However, subunit pPslq1a forms smaller masses than unit pPslq1. K-feldspar porphyroclastic quartz monzonite (pPslq2) forms kilometric oblong masses that are concentrated in the Nallujuaq Lake and Frichet River area. North of the Naujaat Shear Zone, porphyraceous quartz monzonite (pPslq1a) is the dominant lithology of the Suluraaq Suite.

Dating

None.

Stratigraphic Relationship(s)

The speckled monzodiorite unit (pPslq1) is locally in transitional contact with K-feldspar porphyroclastic quartz monzonite (pPslq2). These two units appear to be comagmatic and unit pPslq2 could be a highly deformed equivalent of unit pPslq1 porphyraceous rocks. These intermediate intrusive rocks of the Suluraaq Suite are cut by a late massive monzodiorite, hololeucocratic and whitish in altered surface.

Different lithologies occur as klippes or folded horizons in sharp contact in unit pPslq2 masses, such as the gabbronorite and mesocratic hypersthene diorite of the Pingasualuit Complex. Unit pPslq1a is in sharp contact and alternating with the Sainte-Hélène Complex.

Paleontology

Does not apply.

References

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