Tectonic evolution of southwestern Newfoundland as indicated by granitoid petrogenesis
Four granitoid suites are recognized in the region of the Cape Ray Fault Zone of southwestern Newfoundland. The two oldest (Ordovician-Silurian (?)) suites represent partial melts of their enclosing host rocks. The Port aux Basques granite is modelled as a partial melt of the gneissic component of its host, Port aux Basques Complex. The Cape Ray granite forms a dominantly tonalitic terrane derived by partial melting of ophiolitic material. The Red Rocks granite and a megacrystic phase of the Cape Ray granite form coherent lines of geochemical descent from the parental tonalite but show evidence of some continental crust contamination. The Late Devonian Windowglass Hill granite is a subvolcanic equivalent of felsic volcanic rocks in the Windsor Point Group. Both units were derived as partial melts of continental crust. The post-tectonic, Late Devonian to Early Carboniferous Strawberry and Isle aux Morts Brook granites constitute the youngest granitoid suite in the region. These A-type granitoids were derived as partial melts of an underlying depleted granulitic (felsic) crust. The depleted nature of the source may have resulted from previous generation of the Windowglass Hill granite and Windsor Point Group. The only possible protolith for the granulitic source is Precambrian Grenvillian gneiss. The presence of this gneiss beneath the Cape Ray Fault Zone of southwestern Newfoundland implies that the complete series of lithologies is allochthonous.