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 degrees counterclockwise bend in the oro genic 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 Provinc e margin, composed of a 1910-1885 Ma continental magmatic are (Burwell domain), indented the Rae Province hinterland during the onset of col lisional orogeny at ca. 1870 Ma (Dn+1). Sinistral transpression at ca. 1845 - 1822 Ma (Dn+2) caused formation of the orogen-parallel Ablovia k shear zone and oblique burial of the Nain Province margin beneath a tilted section of the hot, buoyant magmatic are. Reactivation of the o rogen at ca. 1798 - 1770 Ma (Dn+3) involved crustal-scale flexural sli p folding of the perturbation and simultaneous exhumation of the Burwe ll 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. T he along-strike heterogeneities in the Torngat Orogen document the inf luence 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.