Coeval sedimentation, magmatism, and fold-thrust development in the Trans-Hudson Orogen: propagation of deformation into an active continental arc setting, Wekusko Lake area, Manitoba

Abstract

Early structures in the southeastern part of the Trans-Hudson Orogen (THO), Wekusko Lake area, Manitoba, comprise northwest-verging folds and a set of steep, southeast-dipping faults that occur at a low angle to bedding. Kinematic indicators are rare, however, the vergence of the associated folds supports reverse movement on the faults. These folds and faults formed prior to the peak of regional metamorphism and therefore must correlate with the widely recognised deformational (D2) event which developed pre- to syn-metamorphism and involved development of a regional, south- to southwest-directed fold-thrust belt. The D2 folds and reverse faults in the study area are interpreted to have originally formed as gently dipping, southwest-verging structures, i.e., as inclined folds and thrust faults, which were then rotated into a steep, northwest-verging orientation during later deformation (D3). In the southeastern THO, regional D2 fold and thrust structures are cut by ca. 1839-1830 Ma plutons, indicating that D2 initiated prior to ca. 1839 Ma. Recognition of these structures in the study area, and their relationships to key stratigraphic units, has provided significant insights into the tectonic setting during the regional D2 event. The D2 fold and thrust structures deform ca. 1834 Ma fluvial sedimentary rocks and ca. 1836-1832 Ma volcanic (subaerial) and plutonic rocks with a "continental" arc geochemical signature. These are the youngest known volcanic and sedimentary rocks within the THO. The subaerial deposition of these young rocks was coeval with initiation of D2 deformation in the region. They were then rapidly incorporated into the thrust fault sequence soon after their formation, which suggests that the fold and thrust structures propagated into a zone of active magmatism which must have been located in the foreland to the belt of thrusting and folding.