The Central Mobile Belt of the Appalachian System in Newfoundland varies in width across the island from 130 mi on the northern coast to about 40 mi on the southern coast. Granitic gneisses, metasediments, amphibolites, and mylonites that form the eastern margin of the belt in the north are involved in a major “S” shaped structure, the Hermitage Flexure. This structure brings them into proximity with the present western margin of the belt in southwestern Newfoundland. There the belt is apparently truncated by the Cabot Fault.
Assuming a constant width for the Central Mobile Belt during the developmental stages of the geosyncline, then its southward thinning and partial disappearance can be explained first by open folding of the belt around the Hermitage Flexure and then by westward truncation by left-lateral (sinistral) displacement along the Cabot Fault.