|Author:||Morfin et al., 2015|
|Type area:||NTS sheets 32A10 and 32A07|
|Geological province:||Grenville Province|
Table des matières
The Barrois Complex was introduced by Morfin et al. (2015) during the geological survey of the Chambord, Roberval and Notre-Dame-de-la-Doré region.
Unit mPboi1 consists mainly of orthogneiss. These are very heterogeneous and closely related to paragneiss horizons (mPboi4). Generally, these orthogneiss are whitish grey, fine to medium grained and more or less banded. Their composition is highly variable, but it is usually granodioritic to tonalitic and, more locally, monzogranitic. Ferromagnesian minerals (biotite, brown hornblende) can make up 15 to 25% of the rock.
The gneiss is greyish to pinkish and medium grained. It is granitic in composition with K-feldspar, plagioclase, amphibole and biotite. Orthopyroxene is generally replaced by amphibole or biotite along grain edges, giving the rock a coronitic texture. Gneissosity is mainly marked by the elongation of discontinuous clusters of ferromagnesian minerals that delineate quartzo-feldspathic bands whose grains themselves show a slight preferential flattening perpendicular to foliation.
Unit mPboi2 was only observed in sheet 32A10, mainly in its western portion (Morfin et al., 2015). It consists of orthopyroxene gneissic rocks (charnockite, enderbite), medium-grained and granoblastic. Orthopyroxene is observed in the field and in thin section. It is millimetric in a fine-grained foliated quartzo-feldspathic matrix.
Unit mPboi3 consists of orthogneiss containing decimetric horizons of gneissic amphibolite, medium-grained, more or less boudinaged and migmatitized. Orthogneiss resembles that of unit mPboi1. Dark green to black amphibolites are composed of plagioclase, hornblende and locally clinopyroxene. They are regularly magnetic, generally fine grained and relatively homogeneous. When present, pyroxene is usually very minor (<1% of the rock). Amphibolites contain medium-grained leucocratic clusters locally. These are interpreted as leucosome when associated with mafic clusters.
Unit mPboi4 consists of paragneiss within orthogneiss of the complex’s other units. Paragneiss is banded and is generally differentiated from orthogneiss by a greater proportion of biotite, making it more mesocratic. Sillimanite and garnet are locally present. Garnet occurs as lilac-pink porphyroblasts that can grow to centimetric size. Sillimanite is fibrous and can represent up to 10% of the rock. It is locally associated with minor amounts of graphite (1-2% of the rock). Paragneiss is migmatitic and the whitish to pinkish mobilisate is granitic. Contact between paragneiss and orthogneiss is not observed. Two informal subunits were identified by Morfin et al. (2015). The work of Moukhsil and Daoudene (2019) did not distinguish them on maps because of their non-mappable size at the 1:50 000 scale.
Barrois Complex 4a (mPboi4a): Rusty Garnet-Sulphides-Graphite Paragneiss
Subunit mPboi4a is a rusty paragneiss containing up to 2% sillimanite, 5% pyrite and 2-3% graphite flakes a few millimetres thick.
Barrois Complex 4b (mPboi4b): Paragneiss with Quartzite Interbeds
Subunit mPboi4b consists of a paragneiss containing quartzite horizons a few decimetres to several metres thick.
The Barrois Complex outcrops mostly in sheet 32A10 where it occupies more than 50% of the area (Morfin et al., 2015). It also occupies ~20% of sheet 32A07 area, where it forms a large NNW-SSE-oriented horizon over a distance of several kilometres (Moukhsil and Daoudene, 2019).
Informal units of the Barrois Complex form metric to decametric enclaves and tectonic slices in several intrusions of the area (Mimosa, Marianne, Bardeau and Léo plutonic suites). Units of the Barrois Complex are also cut by granitic to syenitic pegmatite dykes and the Claire Gabbronorite.
Does not apply.