First published: 28 October 2020
Last modified:
DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
| Author(s): | Fahrig and West, 1986 |
| Age: | Mesoproterozoic |
| Stratotype: | None |
| Type area: | Schefferville area (NTS sheet 23J15) |
| Geological province: | Churchill Province |
| Geological subdivision: | New Quebec Orogen (Labrador Trough) / Schefferville Lithotectonic Zone |
| Lithology: | Diabase, gabbro |
| Category: | Lithodemic |
| Rank: | Lithodeme |
| Status: | Formal |
| Use: | Active |
None
Background
Several north-trending diabase dykes cut the Kaniapiskau Supergroup in the Schefferville area. The first references to these dykes come from the work of the Geological Survey of Canada (Harrison, 1952; Frarey, 1961), where they are simply referred to as « diabase ». Harrison et al. (1972) then informally introduced the name « Maryjo Diabase » to group these dykes, one of which is well exposed along Maryjo Lake, NE of Schefferville. The name « Maryjo Diabase » was used by Wardle (1979, 1982), but not by Dimroth (1972, 1978) and Fahrig (1976). These authors refer to the dykes as « diabase » and « Schefferville diabase dykes » respectively. The first mention of the name Schefferville Dykes comes from Fahrig and West (1986).
Description
The Schefferville Dykes consist of olivine diabase and gabbro. These dykes are undeformed and weakly altered. The rock is dark greenish grey, fine to medium grained and ophitic. It is mainly composed of plagioclase (labradorite), clinopyroxene (augite) and minor amounts of olivine and trace biotite (Harrison et al., 1972; Zajac, 1974; Dimroth, 1972, 1978). Plagioclase is partly saussuritized. The main accessory minerals are ilmenite, pyrite, pyrrhotite and chalcopyrite (Zajac, 1974). The rock’s relatively low silica (46.45-46.9% SiO2) and high alkali (2.86-3.2% Na2O and 0.9-1.37% K2O) contents suggest an affinity with alkaline basalts (Harrison et al., 1972; Dimroth, 1972, 1978).
Thickness and distribution
The Schefferville Dykes is made of a swarm of discontinuous, echelon dykes that are oriented N-S to NNW-SSE. This swarm was mapped south of latitude 55° N in the southern part of the Labrador Trough (Frarey, 1961; Harrison et al., 1972; Dimroth, 1972, 1978; Zajac, 1974; Wardle, 1979, 1982). In Quebec, these dykes are concentrated between Hayot Lake and the Schefferville area (sheet 23J15). Dimroth (1978) indicates that some dykes cut the western edge of the Labrador Trough, south of Schefferville. According to Harrison et al. (1972), the dykes’ thickness is ~30 m. Magnetic lineaments suggest that the dykes are followed over a distance of ≥25 km in Quebec.
Dating
The Schefferville Dykes are Mesoproterozoic in age (~1325 Ma, according to Fahrig and West, 1986) and represent the youngest igneous rocks of the Labrador Trough in the Schefferville area (Zajac, 1974; Clark, 1994). A crystallization age of 1264 ±70 Ma was obtained by Leech et al. (1963) on a sample of olivine diabase (FA-307-61). Another geochronological study on total rock gave an age of 1146 ±104 Ma (Wanless et al., 1968).
| Unit | Sample Number | Isotopic System | Mineral | Crystallization Age (Ma) | (+) | (-) | Reference(s) |
| mPsch | FA-307-61 | K-Ar | Total rock | 1264 | 70 | 70 | Leech et al., 1963 |
| mPsch | – | K-Ar | Total rock | 1146 | 104 | 104 | Wanless et al., 1968 |
Stratigraphic relationship(s)
The Schefferville Dykes were emplaced hundreds of millions of years after the Hudsonian tectonic phase, during a period of E-W tension (Harrison et al., 1972; Dimroth, 1972, 1978). They cut folded and faulted rocks of the Kaniapiskau Supergroup (Swampy Bay, Attikamagen and Ferriman Groups) located in the Schefferville area (Frarey, 1961; Harrison et al., 1972; Dimroth, 1972, 1978; Zajac, 1974; Wardle, 1979). The Schefferville Dykes have structural similarities with gabbro of the Shabogamo Intrusive Suite in the southern Labrador Trough (Wardle, 1979).
Paleontology
Does not apply.
References
Publications Available Through SIGÉOM Examine
DIMROTH, E. 1972. STRATIGRAPHY OF PART OF THE CENTRAL LABRADOR TROUGH. MRN. DP 154, 304 pages and 6 plans.
DIMROTH, E. 1978. RÉGION DE LA FOSSE DU LABRADOR ENTRE LES LATITUDES 54° 30′ ET 56° 30′. MRN. RG 193, 417 pages and 16 plans.
HOCQ, M., VERPAELST, P., CLARK, T., LAMOTHE, D., BRISEBOIS, D., BRUN, J., MARTINEAU, G. 1994. GÉOLOGIE DU QUÉBEC. MRN. MM 94-01, 172 pages.
Other Publications
FAHRIG, W.F., WEST, T.D., 1986. Essaims de dykes diabasiques du Bouclier canadien. Geological Survey of Canada; Map 1627A. doi.org/10.4095/133917
FRAREY, M.J., 1961. Menihek Lakes, Newfoundland and Québec; Geological Survey of Canada; Map 1087A. doi.org/10.4095/124105
HARRISON, J.M., 1952. The Quebec-Labrador iron belt, Quebec and Newfoundland. Geological Survey of Canada; Paper 52-20, 21 pages. doi.org/10.4095/123923
HARRISON, J.M., HOWELL, J.E., FAHRIG, W.F., 1972. A geological cross-section of the Labrador miogeosyncline near Schefferville, Quebec. Geological Survey of Canada; Paper 70-37, 34 pages. doi.org/10.4095/102389
LEECH, G.B., LOWDON, J.A., STOCKWELL, C.H., WANLESS, R.K., 1963. Age determination and geological studies (including isotopic ages-report 4). Geological Survey of Canada; Paper 63-17, 146 pages. doi.org/10.4095/101067
WANLESS, R.K., STEVENS, R.D., LACHANCE, G.R., EDMONDS, C.M., 1968. Age determination and geological studies, K-Ar isotopic ages, report 8. Geological Survey of Canada; Paper 67-2A, 141 pages. doi.org/10.4095/103342
WARDLE, R.J., 1979. The Western Margin of the Labrador Trough. Department of Mines and Energy, Government of Newfoundland and Labrador; Report 79-1, 7 pages. nr.gov.nl.ca/nr/mines/geoscience/publications/reportactivities/1979/Wardle2_ROA1979.pdf
WARDLE, R.J., 1982. Geology of the south-central Labrador Trough. Government of Newfoundland and Labrador, Department of Mines and Energy, Mineral Development Division, Map 82-005. gis.geosurv.gov.nl.ca/geofilePDFS/ReceivedBatch58/LAB_0603.pdf
ZAJAC, I.S., 1974. The stratigraphy and mineralogy of the Sokoman formation in the Knob Lake area, Quebec and Labrador. Geological Survey of Canada; Bulletin 220, 159 pages. doi.org/10.4095/123946
Suggested Citation
Ministère de l’Énergie et des Ressources naturelles (MERN). Schefferville Dykes. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-du-superieur/dykes-de-schefferville_en [accessed on Day Month Year].
Contributors
First publication | Charles St-Hilaire, GIT, M.Sc. charles.st-hilaire@mern.gouv.qc.ca (redaction) Mehdi A. Guemache, P. Geo., Ph.D. (coordination); anonymous (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); André Tremblay (HTML editing). |