The undeformed Newport megacrystic granite of northwestern Bonavista Bay postdates nearly all the other granites in the area, many of which are strongly cataclastic. It also cuts a regional swarm of diabase dikes. The Rb–Sr isochron of 332 ± 42 Ma for the Newport overlaps the 300 ± 18 Ma isochron age of the deformed Lockers Bay megacrystic granite which is cut both by the Newport and the diabase dikes. This indicates that the emplacement of the Lockers Bay pluton, its deformation, and the intrusion of the diabase dikes and the Newport granite all took place in the interval 290–320 Ma, that is in late Carboniferous times. Major movements along the Dover Fault line, which truncates the Newport in the southeast, probably occurred subsequent to this interval.