Tectonic reactivation of transverse basement structures in the Grenville orogen of SW Quebec, Canada: Insights from gravity and aeromagnetic data

• Basement faults were reactivated in allochtonous belt during grenvillian orogeny.
• Basement faults were reactivated to sinistral shear corridors in the lower deck.
• A megakink were developed during differential post-orogenic collapse in the CMB-Q.
• Distinct deformation responses occur at different crustal levels in the allochtonous belt.
• The Labelle shear zone is interpreted as a late, reverse shear zone.

NW-SE trending, transverse lineaments, including the lithospheric-scale Mont-Laurier lineament, are interpreted from regional Bouguer gravity of the Grenville orogen of SW Quebec and adjacent Superior Craton in southeastern Canada. These lineaments, transverse to the ENE trending Grenville orogen, are inferred to correspond to Palaeoproterozoic structures in Archaean basement that have played an important role: (i) in the development of volcano-sedimentary back-arc basins along this segment of the Laurentian margin; (ii) on the geometry of thrust sheets and folds formed during thrusting in the ca. 1.23–1.2 Ga Elzevirian orogeny and incorporation of the basins within the orogen; (iii) on reorientation of early-formed structures in the Central Metasedimentary Belt of Quebec (CMB-Q) during ca. 1.19–1.17 Ga post-Elzevirian orogenic collapse; and (iv) for development of syn-plutonic deformation corridors and shear zones at the onset of the emplacement of the Morin anorthosite-mangerite-charnockite-granite (AMCG) suite. In the CMB-Q, a 100 km wide megakink zone developed during ca. 1.19–1.17 Ga differential, post-Elzevirian orogenic collapse in the upper-most nappe above transverse sinistral shear corridors 10–20 km wide located in an underlying thrust sheet or “lower-deck”. Emplacement of 1.17 Ga Chevreuil intrusive suite preferentially occurred within the megakink zone, starting late in the post-Elzevirian collapse and culminating during a switch to local shortening early in (and in part as a consequence of) the emplacement of the voluminous Morin anorthosite and associated AMCG-suite plutons. The Labelle deformation zone separating the CMB-Q and Morin terrane is interpreted as a post-Shawinigan, reverse shear zone that truncates folded lithological layering in the eastern CMB-Q and western Morin terrane that is either subsequently folded above the Mont-Laurier lineament during its further reactivation, or developed as a curved shear zone stepping across the Mont-Laurier lineament. The Grenville Province of SW Quebec therefore provides an example of strain partitioning and distinct deformation responses at different crustal levels during reactivation of basement structures.