Along-strike Acadian structural variations in the Quebec Appalachians: Consequence of a collision along an irregular margin

The Quebec Appalachians have been shaped by two major orogenies: the Middle to Late Ordovician Taconian and the Middle Devonian Acadian. Thrust faults and nappe structures characterized the Taconian deformation throughout the Quebec Appalachians, whereas structural styles pertaining to the Acadian orogeny differ from southern Quebec to the Gaspe Peninsula. Structural analysis of Late Ordovician to Middle Devonian supracrustal rocks shows two different Acadian deformational regimes: strike-slip tectonics in the Gaspe Peninsula and thrust or dip-slip tectonics in southern Quebec. In southern Quebec, Acadian regional deformation produced folds which vary from upright to overturned and tight to isoclinal from the NW to the SE. Major faults (e.g., La Guadeloupe) are northwestward directed thrust faults marked by highly ductile shear zones outlined by mylonite. In the Gaspe Peninsula, structural trend is NE and major E-W dextral strike-slip faults transect this trend. Folds are open and upright, inclined and tighter near the major faults where they have a clockwise rotation like the regional cleavage. Major faults (e.g., Grand Pabos) follow corridors delimiting high-strain zones where the fabrics developed are indicative of a ductile-brittle regime of deformation. In the Temiscouata region, major structural features of both southern Quebec and the Gaspe Peninsula are recognized. Structures of this region consist of ENE trending dextral strike-slip faults and high-angle WNW verging reverse faults, parallel to major NNE folds. These structures reflect the transition from purely horizontal movement along major strike-slip faults of the Gaspe Peninsula to vertical movement along thrust faults in southern Quebec. Acadian structural variations within the Quebec Appalachians are interpreted in terms of a continental collision of Gondwana along the irregular margin of Laurentian and its Taconian accreted terranes.