In the Central Metasedimentary belt of the Grenville orogen, we recognize two contrasting packages of rocks within what traditionally has been interpreted as a continuous, intact stratigraphic sequence metamorphosed under upper amphibolite–facies to granulite-facies conditions. The two packages are separated by a thrust fault, the hanging wall of which was transported northwestward relative to rocks of the footwall. Upper greenschist– to lower amphibolite–grade marbles make up the footwall, whereas the allochthon contains granulites, metamorphosed prior to deposition of an unconformably overlying quartzite and intrusion of a compositionally diverse suite of 1179–1162 Ma plutons. Emplacement of the pluton-saturated allochthon occurred at ∼1161 Ma and metamorphosed platformal carbonates into the marbles of the footwall. We interpret this thrust as part of a fundamental suture within the Grenville orogen.