Background and Methodology
The Jean-Marie Structural Domain (DSjme) was defined from a geological mapping survey conducted by Moukhsil and El Bourki (2020) in the Girardville area (NTS sheets 32H02).
Boundaries and Morphology
|~11 km (mean, along an E-W axis)
|~26 km (maximum, along a N-S axis)
|N-S elongation (NTS sheet 32H02)
The Jean-Marie Structural Domain (DSjme) occupies the western part of sheet 32H02. It is bounded to the south by the Lac Rond Structural Domain (DSrnd), and to the east by the Vertu (DSvtu) and Bois Vert (DSbvt) structural domains. The DSjme extends westward in sheet 32H03 and towards the NW and north in sheets 32H06 and 32H07, respectively.
Stratigraphic Units Concerned
Stratigraphic units belonging to the Jean-Marie Structural Domain are:
The Jean-Marie Structural Domain (DSjme) corresponds to the orientation of the planar fabric in units of the Jean-Marie and Bolduc intrusive suites and in the Barrois Complex (mPboi4 and 4c). The planar structure is represented mainly by secondary tectonometamorphic mineral foliation, mylonitic foliation or banding in intrusive rocks, and by gneissosity in metasedimentary facies of the area.
❯ Main Fabrics
The Jean-Marie structural domain is characterized by a homogeneous planar fabric trajectory (Sn) in the different lithostratigraphic units that form it. This planar fabric has an average N-S orientation and an eastward dip (mean Sn foliation: 04°/55°). In rocks of the Bolduc and Jean-Marie intrusive suites, the Sn planar fabric is mainly expressed by a secondary tectonometamorphic mineral foliation or by mylonitic banding in fault zones. This foliation is characterized by the preferential alignment of minerals and, locally, by flattening and grain size reduction in mylonitic zones of the area. In metasedimentary rocks of the Barrois Complex (mPboi4, mPboi4c), gneissosity is characterized by alternating light layers (containing quartz-feldspar) and dark layers (enriched in biotite, magnetite or orthopyroxene).
In general, mineral lineations borne by these planar fabrics are secondary mineral lineations of tectonometamorphic type. Their average orientation is 135° and they have an oblique component (average Ln: 135°/44°). In stereographic projection, these lineations are distributed in particular in the SE quadrant of the canvas with some points in the SW part.
|Type of Fabric
|Dip / Plunge (°)
|Number of Measurements
|Secondary tectonometamorphic mineral foliation, mylonitic foliation or banding, and gneissosity
|Secondary tectonometamorphic mineral lineation
❯ Other Fabrics
On some outcrops of the Jean-Marie structural domain, the Sn planar fabric is cut by a second mineral foliation Sn+1. This is easily recognizable at fold hinges, where minerals generally have a preferential orientation and quartz grains are stretched.
Analysis of the distribution of geophysical lineaments, interpreted from maps of the total magnetic field and its derivatives (Intissar and Benahmed, 2015) and the planar fabric, indicates that the Jean-Marie Structural Domain (DSjme) is affected by at least one folding phase having a mean axial plane orientation N-S to NNE-SSW. At the outcrop scale, isoclinal or symmetrical-style folding has been observed in rocks of the Jean-Marie and Bolduc intrusive suites as well as in enclaves of the Barrois Complex 4 (mPboi4). The stereographic projection of axial planes indicates that folds are overturned towards the east or west.
Geometric Parameters of Regional Folds:
|Fold or Family of Folds
|Type (Anticline, Syncline or Undetermined)
|Shape (Antiform or Synform)
|Attitude (Overturned or Upright)
|Position (Certain or Probable)
❯ Crosscutting Relationships
The Jean-Marie Structural Domain is cut by two families of faults inferred from high-resolution magnetic maps or observations made on outcrops. The first family is N-S to NNW-SSE oriented and is represented by normal and reverse faults of undetermined movement whose orientation is subparallel to the structural pattern interpreted for this domain and which probably played a role in structuring the intrusions of the area. The second family of faults, generally oriented NE-SW, is represented by faults of undetermined movement and by a reverse fault in the SE part of the domain, in contact with the Bois Vert Structural Domain.
Geometric Parameters of Regional Faults Cutting the Jean-Marie Structural Domain:
|Fault or Family of Faults
|Mean Direction (°)
|Mean Dip (°)
|Lineation Plunge in the Fault Plane
|Estimated Width (m)
|Estimated Length (km)
|Family of N-S to NNW-SSE faults
|N-S to NNW-SSE
|Normal, reverse and undeterminate
|Family of NE-SW faults
|Reverse and undeterminate
Does not apply.
The Jean-Marie Structural Domain has undergone moderate to strong deformation characterized by a well-developed planar fabric, which is homogeneous between outcrops of each lithostratigraphic unit. The Sn planar fabric represents the early phase of deformation and is marked essentially by secondary mineral foliation or mylonitic banding in intrusive rocks or by gneissosity in metasedimentary rocks of the area. The domain underwent a second phase of deformation (Sn+1) characterized by folding that indicates E-W compression.
About 30 samples representative of the lithostratigraphic units of this domain (DSjme) were studied under a polarizing microscope to determine the type and spatial distribution of metamorphism. Mineralogical associations and petrographic characteristics of the samples indicate that the temperature and pressure conditions within the domain have largely reached the granulite facies, including a few places at the upper amphibolite facies.
The presence of orthopyroxene and perthite (K-feldspar with albitic exsolution) is evidence of temperature conditions typical of the granulite facies (≥600°C). In places, a biotite-hornblende ferromagnesian mineral assemblage (pyroxene absent) is observed, as well orthopyroxene altering to hornblende or biotite (uralitization) that can be explained by amphibolite facies retrograde metamorphism.
The high-resolution residual magnetic field map (Intissar and Benahmed, 2015) of the Jean-Marie Structural Domain indicates that the geophysical pattern is quite homogeneous, including areas of highly contrasting magnetic susceptibility of high magnetism. In the central part of the domain, the magnetic pattern displays an elliptical ring texture with moderate density magnetic banding in units of the Bolduc (mPblc) and Jean-Marie (mPijm) intrusive suites. Elsewhere, the magnetic pattern is rather banded in the NE part of the domain, but lineaments are curvilinear with an overall moderate to intense magnetic susceptibility.
Does not apply.
Publications Available Through Sigéom Examine
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 et 2 plans.
MOUKHSIL, A., EL BOURKI, M., 2020. Géologie de la région de Girardville, Province de Grenville, région du Saguenay – Lac-Saint-Jean, Québec, Canada. MERN; BG 2021-02, 1 plan.
Ghyslain Roy, P. Geo. (coordination); Fabien Solgadi, P. Geo., Ph.D. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); André Tremblay (HTML editing); Céline Dupuis, P. Geo., Ph.D. (English version).