Synthesis of Palaeozoic deformational events and terrane accretion in the Canadian Appalachians

Abstract

Plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion, with some deformation associated with transform/transcurrent movements. Deformation associated with subduction varies between two end members: (1) where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes, a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over-riding 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 Canadian Appalachians correspond to narrow diachronous events in the Ordovician and Silurian, whereas Devonian, Carboniferous and Permian deformational events are widespread and broadly synchronous. Along the western 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 Victor and various ophiolitic massifs (volcanic arc and peri-arc terranes) over cratonic North America. Within the eastern half of the Central Mobile Belt, the Late Cambrian-Early Ordovician Penobscotian deformational event corresponds to the ?south-easterly accretion of the Exploits subzone (various volcanic are and peri-arc terranes) over the Gander Zone (?continental rise). In the centre of the orogen, the Late Ordovician-Silurian Beothukan deformational event corresponds to the south-easterly accretion of the Notre Dame over the Exploits-Gander subzones. Along the south-eastern side of the Central Mobile Belt, the Silurian Ganderian deformational event corresponds to the north-north-east, sinistral transcurrent accretion of the Avalon Composite Terrane (microcontinent) over the Gander-Exploits zones. Along the south-eastern half of the orogen, the Late Silurian-Middle Devonian Acadian deformation event corresponds to the westerly accretion of the Meguma terrane (intradeep or continental rise) over the Avalon Composite Terrane. Affecting the entire orogen, the Late Devonian, Carboniferous and Permian, Acadian-Alleghanian deformational events correspond to the east-west convergence between Laurentia and Gondwana (continent-continent collision).