Magmatic History of the Avalon Terrane of Southern New Brunswick, Canada, Based on U-Pb (Zircon) Geochronology

Abstract

U-Pb (zircon) dates from volcanic and plutonic units confirm that igneous activity throughout the Caledonian Highlands of southern New Brunswick occurred in two main episodes: ca. 620 Ma and ca. 560-550 Ma. The ca. 620 Ma episode is represented by mainly metatuffaceous rocks of the Broad River Group and associated dioritic to granitic plutons that form most of the eastern highlands. Igneous rocks of similar age and type have been documented in Avalonian areas throughout the northern Appalachian Orogen and are interpreted generally to have formed during subduction at a continental margin. In contrast, the ca. 560-550 Ma igneous episode may be unique to the Caledonian Highlands. It is represented by tuffs and bimodal flows of the Coldbrook Group and co-genetic gabbroic and granitic plutons that occur mainly in the western highlands. This voluminous magmatism may have taken place in a volcanic arc and intra-arc extensional setting, perhaps like that represented by older but lithologically similar rocks of th...