DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Author:||Beaudette et al., 2020|
|Stratotype:||None. Reference outcrop 19-CB-1130 is located 2 km NE of Ammaluttuq Lake|
|Type area:||West-central part of the Parent Lake area (NTS sheet 35G11)|
|Geological province:||Churchill Province|
|Geological subdivision:||Ungava Orogen / Northern Domain|
The Sirluaq Suite was introduced by Beaudette et al. (2020) to individualize massive gabbro intrusions in the Parent Lake area (NTS sheet 35G11). These rocks were previously assigned to the Watts Group (Lamothe, 2007).
The Sirluaq Suite consists of ophitic to subophitic mesocratic gabbro, generally massive and fine to coarse grained. The unit also contains gabbronorite and minor phases of leucogabbro and anorthositic gabbro. Overall, rocks are greenish grey in altered patina and generally dark grey in fresh exposure. Variations in composition and texture are only very locally observed on the same outcrop. Some gabbro layers contain bands with fairly sharp contacts richer in plagioclase or bands of melanocratic gabbro.
The dominant mesocratic phases are composed of equal parts of plagioclase in non-oriented, stocky laths and ferromagnesian minerals in clusters or isolated crystals, generally coronitic. The ferromagnesian minerals are represented in variable amounts by clinopyroxene and hornblende, and to a lesser extent biotite and orthopyroxene. Clinopyroxene is almost completely replaced by hornblende, the latter forming rims around clinopyroxene crystals. Leucogabbro and anorthositic gabbro phases are composed of ≥70% entangled centimetric plagioclase laths completely epidotized. The preferential orientation of plagioclase crystals in certain layers is interpreted as a fabric of magmatic origin. The main accessory minerals are opaque minerals (up to 2%) and, locally, interstitial quartz within plagioclase crystals. Some phases are magnetic, notably gabbronorite. The Sirluaq Suite is marked by a strong positive anomaly on the regional aeromagnetic map.
Thickness and Distribution
The Sirluaq Suite forms two plutons located in the Parent Lake area (sheet 35G11). The first covers an area of 8 km² NE of Ammaluttuq Lake, and the other occupies 2 km² east of Perrault Lake. The rooting thickness of these intrusions is unknown.
No crosscutting relationship with the surrounding units was observed in the field. Rocks of the Sirluaq Suite are massive and interpreted as post-tectonic. They cut the surrounding foliated units, namely the Qikirtalialuk, Foucault and Iqiat suites.
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Publications Available Through SIGÉOM Examine
BEAUDETTE, M., BILODEAU, C., MATHIEU, G. 2020. Geology of the Parent Lake area, Ungava Orogen, Nunavik, Quebec, Canada. MERN. BG 2020-04, 1 plan.
LAMOTHE, D. 2007. Lexique stratigraphique de l’Orogène de l’Ungava. MRNF. DV 2007-03, 66 pages and 1 plan.
Ministère de l’Énergie et des Ressources naturelles (MERN). Sirluaq Suite. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-de-churchill/suite-de-sirluaq_en [accessed on Day Month Year].
Mehdi A. Guemache, P. Geo., Ph.D. (coordination); James Moorhead, P. Geo., M.Sc. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); Ricardo Escobar Moran (HTML editing).