SYNTHESIS OF PALEOZOIC DEFORMATIONAL EVENTS AND TERRANE ACCRETION IN THE CANADIAN APPALACHIANS

Plate tectonic theory predicts that most deformation is associated wit h subduction and terrane accretion, with some deformation associated w ith transform/transcurrent movements. Deformation associated with subd uction varies between two end members: (1) where the tectonic regime i s dominated by subduction of oceanic lithosphere containing small terr anes, a narrow surface zone of accretionary deformation along the subd uction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over-ridi ng plate; and (2) where continent-continent collision is occurring, a wide surface zone of accretionary deformation starts synchronously or with limited diachronism. Palaeozoic deformational events in the Canad ian Appalachians correspond to narrow diachronous events in the Ordovi cian and Silurian, whereas Devonian, Carboniferous and Permian deforma tional events are widespread and broadly synchronous. Along the wester n side of the Canadian Appalachians, the Taconian deformational event starts diachronously throughout the Ordovician and corresponds to the north - north-west accretion of the Notre Dame, Ascot-Weedon, St Victo r and various ophiolitic massifs (volcanic arc and peri-arc terranes) over cratonic North America. Within the eastern half of the Central Mo bile Belt, the Late Cambrian - Early Ordovician Penobscotian deformati onal event corresponds to the ?south-easterly accretion of the Exploit s subzone (various volcanic arc and peri-arc terranes) over the Gander Zone (?continental rise). In the centre of the orogen, the Late Ordov ician - Silurian Beothukan deformational event corresponds to the sout h-easterly accretion of the Notre Dame over the Exploits-Gander subzon es. Along the south-eastern side of the Central Mobile Belt, the Silur ian Ganderian deformational event corresponds to the north - north-eas t, sinistral transcurrent accretion of the Avalon Composite Terrane (m icrocontinent) over the Gander-Exploits zones. Along the south-eastern half of the orogen, the Late Silurian-Middle Devonian Acadian deforma tion event corresponds to the westerly accretion of the Meguma terrane (intradeep or continental rise) over the Avalon Composite Terrane. Af fecting the entire orogen, the Late Devonian, Carboniferous and Permia n, Acadian-Alleghanian deformational events correspond to the east - w est convergence between Laurentia and Gondwana (continent-continent co llision).