Last modification: 10 March 2020
| Author(s) | Moukhsil and Daoudene, 2019 |
| Methodology | Defined from geological survey |
| Geological(s) subdivision(s) | St. Lawrence Platform and Grenville Province |
| Main movement | None |
| Deformation style | Undeformed and subhorizontal bedding |
| Metamorphic facies (mean facies related to main deformation) | Not metamorphosed |
Background and Methodology
The Lac-Saint-Jean Structural Domain was defined following geological mapping surveys conducted by Moukhsil and Daoudene (2019) in the Commissaires Lake area, and by Moukhsil and El Bourki (2020) in the Normandin area.
Boundaries and Morphology
| Width (km) | Undetermined |
| Length (km) | Undetermined |
| Orientation | Undetermined |
To date, the extent and morphology of the Lac-Saint-Jean Structural Domain are unknown. It is exposed in the NE corner of sheet 32A08 from which it extends northward in the central portion of sheet 32A09. The domain also appears to be continuing in sheets 22D05 and 22D12. The presence of sedimentary rock outcrops belonging to the Trenton Group, NE of sheet 22D06 (Hébert and Lacoste, 1998), suggests that at least a portion of the Lac-Saint-Jean Structural Domain could be exposed as a small outlier north of Chicoutimi (Saguenay). By its nature, the Lac-Saint-Jean Structural Domain forms an uneroded klippe, located far NW of the boundary with the Laurentian plateau, of the St. Lawrence Platform Ordovician sedimentary sequence (Brisebois and Brun, 1994).
Ordovician sedimentary rocks of the Lac-Saint-Jean Structural Domain mainly unconformably overlie Mesoproterozoic rocks of several Grenvillian structural domains. These include the Saint-André-du-Lac-Saint-Jean, Bouchette, Sainte-Hedwidge and Patrick Ouest structural domains, as well as the Saint-François-de-Sales Shear Zone (sheets 32A08 and 32A09).
Stratigraphic Units Concerned
The Lac-Saint-Jean Structural Domain contains Ordovician sedimentary rock formations of the Trenton Group, Île aux Couleuvres Formation and Pointe-Bleue Formation.
Structural Characteristics
❯ Main Fabrics
The Lac-Saint-Jean Structural Domain is undeformed, so the main fabric corresponds to bedding, which appears to be subhorizontal overall. However, the stereographic projection of measurements collected in the NE corner of sheet 32A08 and in the southern part of sheet 32A09, following mapping surveys of Morfin et al. (2015), Moukhsil and Daoudene (2019) and Moukhsil and El Bourki (2020), shows that the S0 stratification in this area has a very shallow mean dip of ~10.7° northward. Locally, the S0 stratification has a steeper dip of 50° northward (outcrop 19-AM-120). This outcrop is located in the vicinity of a reverse regional fault which could explain tilting of the S0 structure.
| Main Fabric | Type of Fabric | Direction (°) | Dip (°) | Number of Measurements | Comments |
| Stratification S0 | Bedding | 291 | 10.7 | 21 | 13 measurements were taken in sheet 32A08 and 8 in sheet 32A09; those with excessive or 0° dips have been excluded from statistical processing. |
❯ Other Fabrics
Not observed.
❯ Folds
Not observed.
❯ Crosscutting Relationships
Not observed.
❯ Kinematics
Does not apply.
Deformation Style
Does not apply.
Metamorphic Characteristics
The Lac-Saint-Jean Structural Domain shows no evidence of any metamorphic episode.
Alterations
Not observed.
Geophysical Characteristics
To date, high-resolution magnetic field imaging is only available in the western portion of Lake Saint-Jean (sheets 32A08 and 32A09; Intissar and Benahmed, 2015). It is therefore difficult to determine what the total magnetic field pattern and its derivatives could be domain wide. However, in sheets 32A08 and 32A09, the Lac-Saint-Jean Structural Domain shows areas where susceptibility is highly variable. Some sectors are characterized by magnetic highs, while others have more moderate susceptibility. Furthermore, in sheet 32A09, the magnetic field high-resolution vertical gradient map shows that variations in susceptibility are partly arranged as curvilinear bands, which in some cases extend into neighbouring Grenvillian structural domains. This suggests that the magnetic pattern observed in the Lac-Saint-Jean Structural Domain largely mirrors that of the underlying Precambrian basement.
Chronological Markers
Ordovician sedimentary rocks of the Trenton Group, Île aux Couleuvres Formation and Pointe-Bleue Formation are the youngest in the Saguenay-Lac-Saint-Jean region.
References
Publications available through Sigéom Examine
HEBERT, C., LACOSTE, P. 1998. GEOLOGIE DE LA REGION DE JONQUIERE-CHICOUTIMI (22D/06). MRN. RG 96-08, 34 pages and 1 plan.
BRISEBOIS, D, BRUN, J.1994. La plate-forme du Saint-Laurent et les Appalaches. Dans : HOCQ, M., VERPAELST, P., CLARK, T., LAMOTHE, D., BRISEBOIS, D., BRUN, J., MARTINEAU, G. 1994. GEOLOGIE DU QUEBEC. MRN. MM 94-01, pages 95-120.
INTISSAR, R., BENAHMED, S. 2015. LEVE MAGNETIQUE AEROPORTE DANS LE SECTEUR OUEST DU LAC-ST-JEAN, PROVINCE DE GRENVILLE. MERN, GOLDAK AIRBORNE SURVEYS. DP 2015-06, 7 pages and 2 plans.
MORFIN, S., TREMBLAY, C., SOLGADI, F., MOUKHSIL, A., DAIGNEAULT, R. 2015. GEOLOGIE DE LA REGION DE CHAMBORD, ROBERVAL ET NOTRE-DAME-DE-LA-DORE (FEUILLETS SNRC 32A08, A09 ET A10) ET RECONNAISSANCE DES FEUILLETS 32A06, A07 ET A11. MERN, CERM. MB 2015-07, 69 pages and 5 plans.
MOUKHSIL, A., DAOUDENE, Y. 2019. Géologie de la région du lac des Commissaires, Province de Grenville, région du Saguenay–Lac-Saint-Jean, Québec, Canada. MERN. BG 2019-01.
MOUKHSIL, A., EL BOURKI, M. 2020. Géologie de la région de Normandin, Province de Grenville, région du Saguenay–Lac-Saint-Jean, Québec, Canada. MERN. BG 2020-01, 1 plan.