Crustal-scale flexural slip folding during late tectonic amplification of an orogenic boundary perturbation in the paleoproterozoic torngat Orogen, northeastern Canada

Large variations in metamorphic grade over short distances, disparate orientations and diverse kinematics of contemporaneous structures, and a previously unexplained, 90° counterclockwise bend in the orogenic boundary of the amphibolite- to granulite-facies northern segment of the Paleoproterozoic Torngat Orogen are shown to be the result of multiple tectonic events acting upon an orogenic boundary perturbation. The perturbation was initiated when a promontory on the Nain Province margin, composed of a 1910-1885 Ma continental magmatic arc (Burwell domain), indented the Rae Province hinterland during the onset of collisional orogeny at ca. 1870 Ma (D_n+1). Sinistral transpression at ca. 1845-1822 Ma (D_n+2) caused formation of the orogen-parallel Abloviak shear zone and oblique burial of the Nain Province margin beneath a tilted section of the hot, buoyant magmatic arc. Reactivation of the orogen at ca. 1798-1770 Ma (D_n+3) involved crustal-scale flexural slip folding of the perturbation and simultaneous exhumation of the Burwell domain and the previously buried Nain crust across the Komaktorvik shear zone, which represents a sheared, tightened fold train localized along the western limit of thinned Nain crust affected by preorogenic rifting, but which does not represent a fundamental plate boundary. The along-strike heterogeneities in the Torngat Orogen document the influence of geometrical and competency heterogeneities in the colliding margins on subsequent deformation and the fact that heterogeneities in the deep crust persist through high-grade metamorphism.