AN 1161 MA SUTURE IN THE FRONTENAC TERRANE, ONTARIO SEGMENT OF THE GRENVILLE OROGEN

In the Central Metasedimentary belt of the Grenville orogen, we recogn ize two contrasting packages of rocks within what traditionally has be en interpreted as a continuous, intact stratigraphic sequence metamorp hosed under upper amphibolite-facies to granulite-facies conditions. T he two packages are separated by a thrust fault, the hanging wall of w hich was transported northwestward relative to rocks of the footwall. Upper greenschist- to lower amphibolite-grade marbles make up the foot wall, 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 similar to 1161 Ma and metamorphosed platformal carbonates into the marbles of the footwall. We interpret this thrust as part of a fundamental suture within the Gr enville orogen.