Postcollisional (1.8--1.7 Ga) intracontinental deformation in the Trans-Hudson Orogen (Canada) produced a series of orogen-parallel high-angle faults and folds. In seismic reflection profiles, the faults are imaged by subvertical zones of diffractions and truncated reflections that extend to 4--8 s (12--24 km). The folded and faulted upper part of the crust is underlain by laterally coherent shallow-dipping reflections that are locally bounded by discrete, highly reflective zones. These zones are interpreted as detachments (shear zones) and can be traced from the upper to lower crust, where some of them appear to pass into laterally continuous reflections that define the Moho. Two distinct regimes of postcollisional crustal deformation are inferred from the seismic images: high-angle faulting and lateral block extrusion in the upper crust and low-angle ductile shearing in the mid/lower crust. The surface geology indicates that the faults resulted in southwest (orogen-parallel) extrusion of the orogen's internal zone relative to the bounding Archean Hearne and Superior cratons. Faulting was concurrent with the development of upright folds with trends that are subparallel to the extrusion direction. The seismic images suggest that the high-angle fold/fault structures are kinematically linked to low-angle detachments represented by laterally coherent, highly reflective zones. The detachment shear zones are inferred to have a top-to-the-southwest sense of shear associated with a subhorizontal, northeast-southwest extension direction, parallel to those observed for 1.83--1.80 Ga collisional shear zones exposed in major postcollisional fold culminations. Long-lived orogen-parallel extension is interpreted as a consequence of the boundary conditions imposed by the northeast trend of both the Superior and Hearne margins. ¿ American Geophysical Union 1996