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:||Reference outcrop 19-GL-2108 is located north of Katsuaq Lake|
|Type area:||Bélanger Lake area, Nunavik (NTS sheet 35G06)|
|Geological province:||Churchill Province|
|Geological subdivision:||Ungava Orogen / Southern Domain|
|Lithology:||Clastic sedimentary rocks (conglomerate and arenite)|
Table des matières
Beaudette et al. (2020) introduced the Hubert Formation to individualize sedimentary beds unconformably overlying (angular discordance) the Chukotat Group. These beds had already been mentioned by Roy (1989), Moorhead (1989) and Barrette (1990b), without, however, recognizing the angular unconformity observed more recently (Beaudette et al., 2020).
The Hubert Formation consists of coarse silicoclastic beds of pebble conglomerate and sandstone having a brick-red patina and fresh surface. The presence of conglomerate beds and thin (4-40 cm) sandstone beds displaying parallel laminae, as well as the absence of fine deposits, imply a proximal energetic deposition environment probably of fluvial origin. Parallel laminations and several erosion surfaces allow the measurement of primary bedding with normal polarity towards the NW. The Hubert Formation is not magnetic.
Polymictic conglomerate contains joint fragments; the proportion of the sandy matrix is <20% and generally almost non-existent. Fragments are 5 mm to 25 mm in size. They consist mostly of angular reddish aphanitic volcanic rock fragments (20-90%), subangular to subrounded aphanitic or very fine-grained greenish grey rock fragments interpreted as being of volcanic origin (up to 15%) and, in smaller amounts, subrounded milky chert fragments (up to 5%), rounded massive gabbro fragments (up to 5%) and subrounded to rounded massive or foliated intermediate to felsic intrusive rock fragments (0-15%). Clastic sequences display normal sorting towards the NW. They consist of conglomerate covering a thickness of 50 cm to 2 m at the base and overlain by a sandstone bed 5 cm to 40 cm thick. The latter is generally truncated by the erosion surface of the next sequence.
In thin section, arenite is composed of an assemblage of subangular quartz and rarely twinned feldspar grains (50%), chlorite (30%) and interstitial carbonates (5%), as well as disseminated hematite (10%) and epidote (10%), as well as trace amounts of muscovite flakes. Epidote is heterogeneously distributed, either disseminated in the matrix or in clusters.
Conglomerate is characterized by a very low spaced schistosity defined by the local orientation of fragments and muscovite flakes observed in thin section. The difference between primary bedding (245°) and foliation (260°) is 15°.
The unconformity carries native copper mineralization (Dryade mineralized zone).
The Hubert Formation outcrops as elongated sedimentary basins of modest dimensions with a surface area of ≤1 km2. Outcrops are located at the structural and stratigraphic summit of the Chukotat Group, directly south of the boundary between the Northern and Southern domains, in the wall of the Bergeron Fault. The true thickness of the formation observed on outcrop 19-GL-2108 is ~90 m.
The Hubert Formation unconformably overlies (angular discordance) basalt of the Chukotat Group. The unconformity was directly observed on geofiche outcrops 19-GL-2108 and 19-GM-5188. It is marked by high hematitization of the underlying volcanic rocks. Its stratigraphic position and the fluvial origin of deposits imply the emergence of the Southern Domain before collision with the Northern Domain. Although volcanic fragments are undoubtedly the product of erosion of Chukotat Group basalt, the origin of intrusive rock fragments remains to be determined. The study of detrital populations will help define the sources and validate the hypothesis stated above if ages correspond to those of the Superior Province. If not, the Hubert Formation could represent a syn-tectonic basin resulting from collision of the Northern and Southern domains.
No fossils reported.
BARRETTE, P D. 1990. GEOLOGIE DE LA REGION DU LAC BOLDUC (FOSSE DE L’UNGAVA). MRN. ET 89-03, 48 pages and 3 plans.
BEAUDETTE, M., BILODEAU, C., MATHIEU, G. 2020. Geology of the Parent Lake Area, Ungava Orogen, Nunavik, Quebec, Canada. MERN. BG 2020-04, 1 plan.
MOORHEAD, J. 1989. GEOLOGIE DE LA REGION DU LAC CHUKOTAT (FOSSE DE L’UNGAVA). MRN. ET 87-10, 64 pages and 2 plans.
ROY, C. 1989. GEOLOGIE DE LA REGION DU LAC BELANGER – FOSSE DE L’UNGAVA – RAPPORT FINAL. MRN. MB 89-13, 119 pages and 1 plan.
Ministère de l’Énergie et des Ressources naturelles (MERN). Hubert Formation. Quebec Stratigraphic Lexicon. http://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-de-churchill/formation-hubert_en [accessed on Day Month Year].
Guillaume Mathieu, Eng., M.Sc. email@example.com (redaction)
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); André Tremblay (HTML editing).