Structural patterns and tectonic evolution of supracrustal domains in the Archean Slave Province, Canada

Abstract

A new plate-tectonic model accounts for lithological relations and regional structural patterns in late Archean supracrustal domains of the Slave Province. Multiple dykes and pillowed mafic flows, most common in the western part of the province, suggest sea-floor spreading. The mafic volcanics, lying in narrow homoclinal belts stratigraphically below more extensive turbidites, are viewed as megaxenolithic remnants of oceanic crust preserved on the periphery of granitoid plutons and blocks of sialic crust. Closure of an oceanic basin was marked by emplacement of the granitoid plutons and coeval felsic volcanics, the latter predominating over mafic volcanics in northeastern domains. The felsic calc-alkaline magmas may have risen from a shallow-dipping subduction zone. Westerly verging folds, westerly convex fold arcs, and inclinations of later foliations, particularly in lower level rocks of higher metamorphic grade, are in accord with underthrusting to the east. The zone of underthrusting shifted progressively westward, and calc-alkaline magmatism swept across the western part of the province. Plutons followed crustal fracture systems, some of which were inherited from initial rifts, producing a rectilinear zigzag pattern of contacts between plutons, and mafic volcanics. The fracture systems and rising plutons redirected stresses, resulting in distinctive sets of regional and local foliations that reflect crustal compression only indirectly related to the sense of subduction.