A REVIEW OF THE GEOLOGY OF THE ANTIGONISH HIGHLANDS, AVALON TERRANE, NOVA SCOTIA

The Antigonish Highlands (Avalon terrane, mainland Nova Scotia) are predominantly underlain by the ca. 620-608 Ma Georgeville Group (GG), which records the development of an intra-arc basin. Arc-related felsic and mafic volcanics are coeval with rift-related tholeiites, and are overlain by a thick sequence of turbidites with minor tholeiites. This magmatism is a local representative of regional arc magmatism along northern Gondwana. Detrital zircon data indicate that the turbidites were derived from Amazonia. Polydeformation of GG was accompanied by lower greenschist facies metamorphism. Intrusion of mafic to felsic plutonic complexes (e.g. 607 + 2 Ma Greendale Complex) occurred during the later stages of deformation. The limited time gap between deposition, deformation and intrusion suggests that GG deposition occurred in a strike-slip basin within the arc. Cambrian-Early Ordovician rocks unconformably overlie GG and are divided into two groups. The Iron Brook Group consists of red conglomerate and red slate overlain by Early Cambrian limestone with cosmopolitan Acado-Baltic fauna. The McDonalds Brook Group consists of red conglomerate and shale overlain by bimodal rift-related volcanics and was probably deposited in a pull-apart basin associated with regional San Andreas-style faulting along the northern Gondwanan margin. By 460 Ma, Avalonia was a microcontinent. Bimodal volcanics were emplaced in an ensialic arc. Early Silurian-Early Devonian clastic rocks (Arisaig Group) were deposited during accretion to Baltica (Early Silurian) and to Laurentia (middle Silurian). The Late Devonian McArras Brook Formation was deposited during post-accretionary strike-slip tectonics along the Laurentian margin. Along the southern flank of the highlands, Late Devonian-Early Carboniferous clastic rocks (St Marys Basin) were deposited and deformed during progressive dextral shear along the Avalon-Meguma boundary during convergence between Laurentia and Gondwana.