Structure of the Lac Nominingue - Mont-Laurier region, Central Metasedimentary Belt, Quebec Grenville Province

The Lac Nominingue - Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation - transposed compositional layering (S-1; host to peak-pressure parageneses) has been folded by isoclinal folds (F-2 and F-3) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F-3 folds, indicating that 1.20-1.18 Ga granulite-facies metamorphism post-dated D-3. D-3 structures are cut by ductile shear zones and boudinaged in D-4 and are folded by regional-scale, open, upright north-south folds (F-5). Folds with shallowly dipping axial surfaces (F-6) are subsequently developed in the Sourd group. F-5 (and probably F-6) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the Nominingue-Cheneville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F-8) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F-2 to F-5 folds may have formed during either subhorizontal, east-west contraction or east-west extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESE-WNW contraction and NNE-SSW (orogen-parallel) extension in D-7 syn- to post-intrusion of the Chevreuil suite. F-8 folds imply a late, Grenvillian SSE-NNW contraction.