Cambro-Ordovician continental-margin rocks of the Humber zone of the Quebec Appalachians were mainly deformed during the Taconian orogeny (Middle Ordovician to Early Silurian). Two Taconian deformational events are recorded west of the Sutton–Notre-Dame mountains anticlinorium axis. They are characterized, respectively, by northwest-directed faulting and synmetamorphic folding (D1−2) and by southeastward back-thrusting motion (D3); the latter deformation has previously been poorly documented in the Quebec Appalachians. This duality of structural vergence is probably induced by the progressive tectonic wedging of basement rocks during a nearly constant northwest–southeast Taconian shortening. In correlative higher grade metamorphic rocks of New England, back-thrusting structures (D3) have not been described and are most probably absent because their root zone is located well above the present-day erosional surface of that part of the Appalachian belt.

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