Distribution and characteristics of Taconian and Acadian deformation, southern Québec Appalachians

Abstract

The regional structure of the southern Quebec Appalachians is redefined in terms of superposed Taconian and Acadian deformation events. Taconian structures and metamorphism dominate in Cambro-Ordovician rocks west of the Baie Verte-Brompton Line (BBL). The Taconian orogen is subdivided into a northwestern external zone, composed of fault-imbricated continental rocks displaying single-phase foreland structures, and a south-eastern internal zone of polydeformed and metamorphosed continental and oceanic rocks. The structural relationships of Cambro-Ordovician rocks astride the BBL demonstrate that the continent-ocean contact was deformed by both southeast-verging late Taconian and upright Acadian folds. East of the BBL, syn- and post-Taconian rocks were mainly affected by Acadian deformation. The Acadian external zone consists of Cambro-Ordovician and post-Ordovician rock units characterized by a single phase of folding. The zone is bounded to the southeast by the Riviere Victoria fault. The Acadian internal zone displays polyphase deformation in the easternmost part of the Quebec Appalachians. The Acadian deformation shows a significant overlap with Taconian structures and metamorphism, and structural windows of the Taconian orogen are found within both the external and internal zones of the Acadian orogen.