|Author:||Leclair et al., 1998|
|Type area:||Bermen Lake area (NTS sheet 23F)|
|Geological province:||Superior Province|
|Geological subdivision:||Ashuanipi, La Grande and Opinaca subprovinces|
Table des matières
The Viau Suite was introduced by Leclair et al. (1998) in the Bermen Lake area to describe two biotite-fluorine-magnetite syenogranite post-tectonic intrusions. Subsequently, several other intrusions were assigned to the Viau Suite in the Nitchequon Lake (Lamothe et al., 2000), Hurault Lake (Thériault and Chevé, 2001), Caniapiscau Reservoir (Simard et al., 2009) and Lake Léran (Talla-Takam et al., in preparation) areas. The Viau Suite is also described in the Ashuanipi Subprovince geological and metallogenic synthesis (Simard et al., 2015).
The Viau Suite groups several subcircular anorogenic granite intrusions (Simard et al., 2015). It has been divided into two units: nAvia2 and nAvia3. This nomenclature is retained to facilitate the link between the synthesis map and maps of the various previously published reports. Thus, the Viau Suite does not have a nAvia1 unit (Simard et al., 2015).
The Viau Suite consists of pinkish biotite-titanite-magnetite ± hornblende syenogranite and monzogranite displaying a porphyraceous or pegmatitic texture, which generally form the pluton edge phase (nAvia2). The core of plutons is occupied by alkaline granite (nAvia3) which is distinguished from the edge phase by a redder colour and the presence of interstitial fluorine (Simard et al., 2015). Rocks are characterized by very high contents of rare earth elements and other incompatible elements (i.e. Hf, Nb, Rb, Th, Y). The presence of fluorine, combined with the very high enrichment in incompatible element, suggests that these intrusions are A-type granites (i.e., anorogenic; Thériault and Chevé, 2001).
Unit Avia2 is the most common. It consists of homogeneous and massive pinkish biotite-titanite-magnetite ± hornblende syenogranite and monzogranite. The rock is medium to coarse grained and generally displays a porphyraceous or pegmatitic texture (Simard et al., 2015). Myrmekitic textures between quartz and plagioclase are also common (Thériault and Chevé, 2001). This unit usually forms the edge phase of Viau Suite intrusions (Simard et al., 2015).
In thin section, K-feldspar occurs as subhedral phenocrystals and euhedral interstitial grains. Subhedral olive-green biotite is partially chloritized. Titanite forms subhedral to anhedral crystals often associated with magnetite, biotite and apatite. Locally, euhedral allanite crystals reach 3 mm in length (Thériault and Chevé, 2001).
Unit Avia3 usually occupies the central part of plutons, is a biotite-magnetite alkaline granite that differs from rocks of unit Avia2 by a more reddish colour and the presence of interstitial fluorine (Simard et al., 2015). Allanite is also observed in this unit (Talla-Takam et al., in preparation).
The Viau Suite groups several subcircular granite intrusions corresponding to strong positive aeromagnetic anomalies located in the southwestern Ashuanipi Subprovince. These intrusions are concentrated along a NE-oriented corridor ~80 km by 200 km, extending from Naopocane Lake to Caniapiscau Reservoir (Thériault and Chevé, 2001). Some intrusions are also located directly to the south, in the Opinaca Subprovince (Simard et al., 2015).
A U-Pb dating returned a crystallization age of 2571 ±2 Ma in a fluorine syenogranite of the Bermen Lake area (David and Parent, 1997). Another U-Pb dating gave a crystallization age of 2572 ±1 Ma in a fluorine granite of the Nitchequon Lake area (Parent, 1998). The Viau Suite is thus the youngest Archean unit known to date in the Ashuanipi Subprovince.
|Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||2571||2||2||David and Parent, 1997|
The Viau Suite intrudes into several geological units of the Ashuanipi Subprovince and, to a lesser extent, into the La Grande and Opinaca subprovinces, including the Grosbois Complex, the Opiscotéo, Gamart and Lataignant suites, and the Mercator Formation.
Does not apply.