Silurian plutonic suites in the Newfoundland Appalachians include abundant gabbro, monzogabbro and granite to granodiorite and lesser quartz diorite and tonalite. Most are medium- to high-K, but included are some low-K and shoshonitic mafic compositions. Felsic rocks are of both alkaline (A-type or within-plate granite (WPG)) and calc-alkaline volcanic arc granite (VAG) affinity. Mafic rocks include both arc-like (Nb/Th < 3) calc-alkaline and non-arc-like (Nb/Th > 3) transitional calc-alkaline basalt to continental tholeiitic affinity compositions. εNd(T) values range from − 9.6 to + 5.4 and δ18O (VSMOW) values range from + 3.1 to + 13.2‰.