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

Abstract

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.

Pre-Carboniferous, episodic accretion-related, orogenesis along the Laurentian margin of the northern Appalachians

“…Investigations in southern Quebec (e.g. Castonguay et al 2001Castonguay et al , 2007 and Gaspé (Sacks et al 2004;Pinchivy et al 2003) revealed a comparable Taconic movement picture involving both orthogonal westdirected thrusting and oblique -dextral tectonic transport near the Baie Verte-Brompton line.…”

“…Tremblay & Pinet 1994;Waldron et al 2003), locally seems to have continued until 450 -445 Ma in parts of New England (e.g. Ratcliffe et al 1998Ratcliffe et al , 1999 and Quebec (Sacks et al 2004), possibly due to convergence driven by subduction rollback of old oceanic lithosphere trapped in re-entrants in the Laurentian margin. Blueschists and eclogites in the Piedmont of the southern Appalachians, Vermont, southern Quebec and the west of Ireland, which mainly involved rocks of the continental margin, yielded ages between 470 and 459 Ma (Laird et al 1993;Chew et al 2003;Miller et al 2006).…”

Hinterland-directed transtensional faulting at an orogen structural front: The example of the Cap-Chat melange, Quebec Appalachians

“…In Figure 10B, the proto-Cap-Chat mélange is envisioned as the westernmost expression of an orogen-scale zone of mechanical decoupling in the upper crust, allowing faulting and block tilting in its hanging wall. In such a model, Silurian normal or transtensional faults documented in the inner part of the Taconian orogen (Sacks et al, 2004;Tremblay and Pinet, 2005) and in the Gaspé belt sedimentary basin just south of the Shickshock-Sud fault (Bourque, 2001) may branch on this decoupling zone.…”

Reconstruction of Taconian and Acadian paleostress regimes in the Quebec and northern New Brunswick Appalachians

“…Since milestone studies by Rodgers (1970), Bird and Dewey (1970), and Williams (1979), among others, many structural analyses have been directed toward the kinematics of major ductile faults at terrane boundaries (Stanley and Ratcliffe 1985;Tremblay et al 1989;Kirkwood et Malo 1993;Sacks et al 2004). Their findings have been essential to understanding the dynamics of deformational processes and the direction of the tectonic transport.…”