|Author:||Goutier et al., 2001a|
|Reference section:||Reference outcrop 2014-JG-2088, located along the Transtaïga Road; sampled for U-Pb isotopic dating.|
|Type area:||SE area of La Grande 3 Reservoir, centre of NTS sheet 33G12 (Bezier Hill). Bezier Hill is now an island as a result of the creation of the La Grande 3 Reservoir. Representative outcrops are visible on the shores of the islands. The main pluton also outcrops along the Transtaïga Road (in sheet 33G05).|
|Geological province:||Superior Province|
|Geological subdivision:||La Grande and Opinaca subprovinces|
|Lithology:||K-feldspar porphyritic quartz monzodiorite, quartz monzodiorite, monzodiorite and granodiorite|
Table des matières
The first mention was used as “Bezier Pluton (Abez)” by Goutier et al. (2001, 2002). This unit was subsequently elevated to the suite rank in the preliminary report prepared by Bandyayera et al. (2013) to group plutons of similar composition. Subsequently, Goutier (2018) added the western end of the main pluton to sheet 33F08, while Goutier et al. (in preparation) described other similar plutons in sheet 33H12. One of the important features is the emplacement of this suite at the interface between the La Grande and Opinaca subprovinces. Intrusions previously defined as belonging to the Bezier Suite and present only in the Opinaca Subprovince were re-assigned to the Féron Suite. These changes relate to five intrusions on sheets 33G06 and 33G07.
The Bezier Suite defined by Goutier et al. (2001a) consists of a K-feldspar porphyritic quartz monzodiorite and local quartz monzodiorite, monzodiorite and granodiorite. The various plutons in this suite are generally well visible on aeromagnetic maps because the delineation coincides with positive magnetic anomalies (Bandyayera et al., 2013). The exception is the pluto found in sheet 33G06. It occurs in an area of low magnetic susceptibility with a few small, poorly defined areas of higher susceptibility. Although its magnetic signature is weaker than other plutons in the Bezier Suite, it has the same lithological characteristics.
One of the determining factors is belongingness in the La Grande Subprovince. The main intrusion cut units in both the La Grande and Opinaca subprovinces. Units located in the La Grande Subprovince previously assigned to the Bezier Suite were re-assigned the Féron Suite.
The rock is greyish to whitish and its fresh surface is greenish to pinkish grey. Its grain size varies from medium to coarse and its structure is massive to slightly foliated. It is characterized by the presence of K-feldspar phenocrystals (6-12%) ranging in size from 0.5 to 3 cm. Feldspars are rectangular to square and zoned; they contain hornblende or biotite inclusions between growth rings. This growth zoning with mineral inclusions is one of the features of the Bezier Suite that distinguishes it from the Radisson Pluton. In addition to being in inclusion in feldspars, hornblende and biotite account for a large proportion of the rock (20-50%). Accessory minerals are magnetite, titanite and epidote.
It is very common to observe centimetric fusiform enclaves of amphibolite and diorite (~3%). Bandyayera et al. (2013) also described the presence of 5% metric enclaves of fine-grained and foliated amphibolite and 3% centimetric angular fragments of mafic to intermediate composition.
Several plutons of a similar nature were identified in the northern region of sheets 33G05, 33G06 and 33G11 (Goutier et al., 2002), in sheets 33G02, 33G07 and 33G10 (Goutier, 2018), 33G09 (Bandyayera et al., 2013), and 33H12 and 33H13 (Goutier et al., in preparation).
The Bezier Suite has nine separate intrusions covering an area of approximately 700 km² and spread in eleven sheets: 33F08, 33G05, 33G06, 33G09, 33G10, 33G11, 33G12, 33G14, 33H13 and 33H14.
The first U-Pb isotopic dating (2674 ±12 Ma) of a K-feldspar porphyritic granodiorite from Guyer Lake (sheets 33G06-33G11) was performed by St. Seymour et al. (1989). This pluton and age have been associated with the Bezier Pluton since the few pluton outcrops have similar petrographic characteristics. Since it was not possible to find an outcrop in the coordinate area of sample LE-132 from St. Seymour et al. (1989), a new sample was taken along the Transtaïga Highway (outcrop 2014-JG-2088) in the main pluton. The latter gave an older age to 2712.3 ±5.8 Ma. From now on, that age is the one assigned to the Bezier Suite.
|Isotopic System||Mineral||Cristallization Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||2712.3||5.8||5.8||David, J., personal communication, 2017|
|U-Pb||Zircon||2673||12||12||St. Seymour et al., 1989|
Units of the Suite of Bezier cover a large area in the Eeyou Istchee James Bay region, over a width of 150 km. Moreover, they cut numerous various lithologies. These relationships are highlighted by dating or field observations.
Does not apply.