Seismic images from a 250 km Lithoprobe reflection profile in the interior of the eastern Grenville province provide important new constraints on the crustal architecture of this part of the orogen. Prominent upper-crustal reflections can be correlated with exposures of high-pressure metamorphic rocks in the Manicouagan shear belt, providing the first direct evidence for eclogite reflectivity in the Grenville province. The eclogites are cut by major late Grenvillian normal faults that penetrate the deep crust and preserve evidence of extensional collapse of the overthickened orogen. North-to-south crustal thinning, indicated by a change in Moho reflection time from 16 to 13 s, correlates well with regional Bouguer gravity trends and is accompanied by a dramatic increase in the reflectivity of the lower crust. These features underscore the significance of recently recognized along-strike variations in tectonic style within the Grenville province and point to the internal complexity that characterizes the root zones of collisional orogens.