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Zeni Shear Zone
Structural label: ZCzen

First publication: 19 February 2019
Last modification:
Author(s) Taner, 1992
Methodology Defined from a geological survey
Belonging Churchill Province Mistinibi-Raude Lithotectonic Domain
Main movement Dextral
Deformation style Anastomosed
Metamorphic facies (mean facies related to main deformation) Amphibolites

Background and Methodology

The Zeni Shear Zone (ZCzen) was described by Taner (1987, 1992) as the “Deformation Zone South of Zeni Lake”. Hammouche et al. (2011) replaced this term with the “Zeni Shear Zone” during mapping.

 

Boundaries and Morphology

Width 13 km
Length 40 km
Orientation ESE-WNW

 

The ZCzen is a 5 km to 13 km wide corridor that spans nearly 65 km in Quebec and continues in Labrador. To the west, it is truncated by the Rivière George Shear Zone (ZCrge) (Vanier et al., 2018). In Quebec, the Mesoproterozoic Ramusio Granite intrusion partially masks the eastern extension of this shear zone.

 

Stratigraphic Units Concerned

Mylonitic zones associated with the ZCzen mainly affect lithologies of the Zeni Complex.

 

Structural Characteristics

The ZCzen consists of several protomylonitic to mylonitic zones between which units are affected by strong planar and linear deformation.

❯ Main Fabrics

The main fabrics of this shear area are well-developed secondary tectonometamorphic foliations (Sn), steeply dipping towards the NE and which include, in some cases, a strong subhorizontal stretch lineation (Ln). There are also protomylonitic and mylonitic foliations or banding.
Main Fabric Type of Fabric Direction (°) Dip / Plunge (°) Number of measurements Comments
Foliation Sn Foliation, gneissosity, mylonitic foliation or banding, schistosity 304 81 195  
Lineation Ln Lineation 125 10 15

 

 

❯ Other Fabrics

Not observed.

 

❯ Folds

Not observed.

 

❯ Cross-Cutting Relationships

The Adelaide Fault is a branch south of the ZCzen that deforms an amphibolite strip of the Zeni Complex, in addition to separate orthogneiss of the Elson Complex in the west from those of the Jannière Complex in the east. Its presence and trace were inferred by Hammouche et al. (2012) from the geophysical survey. According to magnetic lineaments, the Adelaide Fault is cut by the ZCzen and ZCrge. The ZCzen is itself cut to the west by the ZCrge; at this location, positive magnetic anomalies corresponding to the Zeni Complex are also shifted according to a dextral movement.

Geometric Parameters of the Adelaide Fault:

Fault or Family of Faults Type Mean Direction (°) Mean Dip (°) Lineation Plunge in the Fault Plane Estimated Width (m) Estimated Length (km) Apparent Movement Position Comments
Adelaide Fault Shearing N-S Undetermined Undetermined Undetermined 20 Undetermined Uncertain, deduced from geophysical survey  

 

❯ Kinematics

The only kinematic indicators observed are sigma-type feldspar porphyroclasts. They indicate dextral horizontal movement (Hammouche et al., 2012).

 

Deformation Style

The intensity of deformation within the ZCzen is variable, moving from zones with little deformation to mylonites.

 

Metamorphic Characteristics

ZCzen rocks have been affected by granulite facies metamorphism (Taner, 1992; Hammouche et al., 2012). Taner (1992) observed pyroxenes having undulatory extinction that indicate that deformation is postmetamorphism. Silification and hematitization are superimposed on protomylonitic fabrics near the contact between the Zeni and Jannière complexes.

 

Alterations

Not observed.

 

Geophysical Characteristics

The ZCzen corresponds to a succession of ESE-WNW linear magnetic ridges. The high magnetic susceptibility of this shear zone is attributed to amphibolites and tonalitic to granitic mylonites of the Zeni Complex. The closely alternating magnetic ridges are caused by high transposition of geological contacts parallel to the main shear foliation. Interpretation of geophysical maps also indicates that the ZCzen is truncated by the ZCrge (Vanier et al., 2018).

 

Chronological Markers

The ZCzen deformation is later than 2480 Ma, the crystallization age of a mylonitized felsic rock of the Zeni Complex (David et al., 2009), and prior to the ZCrge deformation, which ended around 1825 Ma (Dunphy and Skulski, 1996).

 

References

Publications available through Sigéom Examine

DAVID, J., MOUKHSIL, A., CLARK, T., HEBERT, C., NANTEL, S., DION, C., SAPPIN, A A. 2009. DATATIONS U-PB EFFECTUEES DANS LES PROVINCES DE GRENVILLE ET DE CHURCHILL EN 2006-2007. GEOTOP UQAM-MCGILL, UNIVERSITE LAVAL, MRNF. RP 2009-03, 32 pages.

HAMMOUCHE, H., LEGOUIX, C., GOUTIER, J., DION, C. 2012. GEOLOGIE DE LA REGION DU LAC ZENI. MRN. RG 2012-02, 35 pages and 1 plan.

HAMMOUCHE, H., LEGOUIX, C., GOUTIER, J., DION, C., PETRELLA, L. 2011. GEOLOGIE DE LA REGION DU LAC BONAVENTURE. MRNF. RG 2011-03, 37 pages and 1 plan.

TANER, M F. 1987. RECONNAISSANCE GEOLOGIQUE DE LA REGION DU LAC JUILLET – NOUVEAU-QUEBEC -. MRN. DP-87-11, 23 pages and 7 plans.

TANER, M F. 1992. RECONNAISSANCE GEOLOGIQUE DE LA REGION DU LAC JUILLET – TERRITOIRE DU NOUVEAU-QUEBEC -. MRN. MB 91-19, 132 pages and 7 plans.

VANIER, M.-A., GODET, A., GUILMETTE, C., HARRIS, L B., CLEVEN, N R., CHARETTE, B., LAFRANCE, I. 2018. Extrusion latérale en croûte moyenne dans le sud-est de la Province de Churchill démontrée par les interprétations géophysiques, l’analyse structurale et les pétrofabriques du quartz. UNIVERSITE LAVAL, INRS, MERN. MB 2018-12, 58 pages.

Other publications

Dunphy, J.M., Skulski, T. 1996. Petrological zonation across the De Pas Batholith: a tilted section through a continental arc? In Eastern Canadian Shield Onshore-Offshore (ECSOOT) Transect Meeting, 1996 (Wardle, R.J. and Hall, J., editors). The University of British Columbia, Lithoprobe Secretariat; Report, 57, pages 44-58.

Vollmer, F.W. 1995. C program for automatic contouring of spherical orientation data using a modified Kamb method. Computers and Geosciences; volume 21, pages 31-49. doi.org/10.1016/0098-3004(94)00058-3

26 août 2020