PLATE TECTONICS DURING THE 1.9 – 1.7 GA ASSEMBLY OF NUNA; EXAMPLES OF MODERN CRUSTAL COLLISION AND TRANSPORT PROCESSES FROM THE SOUTHEASTERN CHURCHILL PROVINCE

Abstract

The Southeastern Churchill Province (SECP) is an elongate Paleoproterozoic-age mobile belt that is part of the Trans-Hudson composite orogen which formed between ca. 1.87 and 1.75 Ga during the amalgamation of the supercontinent Nuna (Columbia). The SECP is on the eastern flank of the large-scale Ungava Indenter system which was the leading edge of the Superior craton during the closure of the Manikewan paleo-ocean. It contains several Archean to Paleoproterozoic crustal fragments which form the Core Zone and is bound to the west by the New Quebec Orogen (NQO), and to the east by the Torngat Orogen (TO). The NQO – Core Zone system preserves thin-skinned as well as thick-skinned tectonic styles and is an ideal area in which to study a complete system of modern-style plate tectonics. The NQO – Core Zone system includes excellent examples of passive margin sedimentation, continental rifting magmatism, ocean-basin closure, back-arc magmatism, and transpressional deformation of all these elements. The collision of the North Atlantic Craton with the Core Zone and subsequently with the Superior Craton produced an oblique collision which resulted in bulk dextral shear that is exceptionally well-preserved in the NQO and between the different crustal blocks of the Core Zone. Several of the crustal scale shear zones that accommodated this movement were reactivated former sutures between blocks or between Core Zone blocks and the Superior or North Atlantic Cratons, thus overprinting the original collisional history in these zones. The rotation of the North Atlantic Craton during the collision, partly due to rotation around the Ungava Indenter, accommodated rigid block extrusion of the crustal fragments that make up the Core Zone along well-defined shear zones. This rigid block extrusion during oblique collision, possibly assisted by lower crustal flow, operated in a manner analogous to the present-day extrusion of Indochina as a result of India – South China convergence and plateau development during the Himalayan Orogen.