|Author:||Talla Takam et al., in preparation|
|Type area:||NTS sheets 33A08, 33A09 and 23D12|
|Geological province:||Superior Province|
|Geological subdivision:||Opatica Subprovince|
|Lithology:||Tonalite, tonalitic gneiss, granodiorite and quartz diorite|
Table des matières
The Misasque River massif was identified by Hocq (1985). He defined this unit as a heterogeneous band of intrusive rocks, leucotonalitic to granitic, between Neptune and Fire lakes (west) to Léran Lake. The area occupied by the Misasque River massif is approximately 1500 km2. Following the summer 2016 geological mapping work, Talla Takam et al. (in preparation) divided the Misasque River massif into different plutons based on their mineral composition, geochemistry and magnetic signature. The Misasque Pluton essentially includes intrusions of tonalite, granodiorite and quartz diorite that are located north of the René Group. It was subdivided into two units by Beauchamp and Massei (2018). The Misasque Pluton became the Misasque Suite due to the varied nature of intrusive rocks included in the unit (Beauchamp and Massei, in preparation).
The Misasque Suite consists of fine to medium-grained, foliated and light grey tonalite and granodiorite. These rocks contain biotite and magnetite, with varying amounts of green hornblende, chlorite and epidote. Mafic minerals are in the form of clusters representing 5 to 15% of the rock. Traces of sphene, apatite and rutile can also be observed. Coarse plagioclase crystals are subhedral, twinned and weakly to strongly altered (sericitized and saussuritized). Biotite is partially to completely chloritized and locally epidotitized. In thin section, tonalite and granodiorite have polygonal and interlobed textures. Quartz grains have a sutured rim and an undulating extinction. Apatite and three types of epidote are also observed in places: allanite, pistachite and clinozoisite. Foliation is marked by the preferential alignment of chloritized biotite and green hornblende when present. The most deformed areas of the suite exhibit L tectonics (outcrops 2016-WM-3781 and 2016-WM-3782). Near the contact with the Laguiche Complex in the north, the Misasque Suite outcrops are hematitized (outcrop 2016-SB-4013) and epidotized (outcrop 2016-SB-4227).
Tonalite and granodiorite outcrops belonging to the Misasque Suite contain in places diorite, quartz diorite, gabbro and, very rarely, paragneiss xenoliths. At least two types of granitic intrusions have been observed, one being intrusions that cut the gneissosity but are also deformed and folded, and the other being straight-line, massive and undeformed dykes composed of granite and pegmatite in several late phases.
Rocks from unit nAmiq1 are more deformed than those of unit nAmiq2. They range from tonalite to tonalitic gneiss and are made up of alternating millimetric to decametric bands of tonalitic, dioritic or granitic composition. Fine-grained, recrystallized gneiss is grey with white, black and locally pink bands. Under the microscope, gneissosity is in the form of alternating mafic horizons (with biotite ± hornblende) and white quartzofeldspathic horizons. The sharp, irregular and very contrasting banding is accentuated by the presence of sub-comformable granitic intrusions.
Rocks of unit nAmiq2 are granodiorites. They therefore contain more K-feldspar and are more rich in potassium (1.82-3.44% K2O, compared to 0.76-1.62% for unit nAmiq1). However, their main geochemical characteristics remain the same as for unit nAmiq1; they are of calc-alkaline affinity, peraluminous and have europium anomalies. These granodiorites show slightly higher magnetic susceptibility on aeromagnetic maps.
From a geochemical point of view, all the rocks of the Misasque Suite are of calc-alkaline affinity. Samples analyzed are enriched in light rare earth elements relative to heavy rare earth elements, with either positive or negative europium anomalies (Eu/Eu* = 0.55 to 2.78). Spider diagrams have negative Nb, Ta and Ti anomalies and Zr and Hf enrichments. The samples are peraluminous (Frost et al., 2001) and plot into the volcanic arc granitoid field (Pearce et al., 1984).
The Misasque Suite is present in the area Léran and Emmanuel lakes (NTS sheets 33A09 and 23D12). It extends more than 75 km in a NNE-SSW direction, from Léran Lake to 15 km north of Cadieux Lake. The Misasques Pluton has a width ranging from 5 to 25 km in a NNW-SSE direction. Its northward extension is limited by the Ribera and Nikos plutons, two plutons that mask the contact between the Opinaca and Opatica subprovinces. To the south, it is in contact with the Upper Eastmain Greenstone Belt. Most of the pluton consists of unit nAmiq1. Unit nAmiq2 is observed in the northwestern portion of sheet 33A08 and in the northern portion of sheet 33A09.
U-Pb analyses gave two age categories for zircons. The oldest is 2822 ±5 Ma and the youngest is 2695 ±8 Ma. The best estimate for the age of magmatic crystallization of the tonalite is 2695 ±8 Ma. Zircons dated to 2822 ±8 Ma would be inherited from an old underlying basement. A rim with low Th/U ratio also yielded an age of 2622 ±16 Ma and would represent the age of a metamorphic event (Davis, personal communication, 2018).
|Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Inherited Age (Ma)||(+)||(-)||Metamorphic Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||2695||8||8||2822||5||5||2622||16||16||Davis, personal communcation, 2018|
The Misasque Suite stratigraphic relationships with rocks of the Opinaca Subprovince are not known at this time. Contact between these units does not occur. In the southern portion, the Misasque Suite intrudes rocks of the Upper Eastmain Greenstone Belt.
Does not apply.