Taconian and Acadian transpression between the internal Humber Zone and the Gaspé Belt in the Gaspé Peninsula: tectonic history of the Shickshock Sud fault zone

The Shickshock Sud fault has a history of Ordovician (Taconian), Silurian (Salinic), and Devonian (Acadian) movements. Taconian deformation involving ductile dextral oblique-slip faulting is recorded in Cambrian rocks in the footwall of the Shickshock Sud fault. Metabasalt and metaarkose at amphibolite grade are converted into phyllonite and mylonitic schist. Shear bands, asymmetric garnet porphyroclasts, C–S fabrics, and mica-fish textures indicate dextral shearing. The regional sense of shear is top to west and southwest on generally southeast dipping shear zones. Hornblende of metabasalt yielded an 40Ar/39Ar age of 455.9 ± 2 Ma, and muscovite from the mylonitic schist yielded an 40Ar/39Ar age of 454.3 ± 0.9 Ma, which indicate metamorphism and deformation during the Taconian orogeny. Evidence for Silurian activity is indicated by the Salinic unconformity to the south related to normal block-faulting. Deformation features in the Ordovician and Silurian–Devonian rocks in the hanging wall were predominantly brittle and involved dextral transpression. Kinematic indicators point to predominantly dextral strike-slip movement. Kinematic analysis of brittle fault-slip data indicates that the shortening axis direction during strike-slip deformation was northwest–southeast and subhorizontal, which is essentially coaxial to the average pole of Acadian cleavage. Deformation in the hanging wall of the Shickshock Sud fault is Acadian-related. The irregular geometry of the Laurentian margin, including the Grenville basement, might be the cause for Taconian and Acadian transpression in the Gaspé Appalachians.