Exploring the link between spatiotemporal patterns of plutonism and geodynamic regimes at the end of Archean: an example from the northeastern Superior Province, Canada

Abstract

This paper presents new U–Pb zircon ages obtained using laser ablation ICP-MS from various plutonic units that intruded along the southern margin of the Bienville domain, a presumed Neoarchean magmatic arc in the northeastern Superior Province, Québec, Canada. The U–Pb ages indicate that the arc plutons were emplaced episodically between ca. 2745 Ma and ca. 2697 Ma, synchronous with regional transpressional deformation. Furthermore, the observed intra-pluton age variations show that the largest examined intrusion, the Radisson pluton, grew incrementally over a period of at least 15 My, perhaps in a series of elongated, sheet-like magma batches straddling the presumed arc margin and emplaced successively, younging inwards. This emplacement style is comparable (though not unique) to modern arc plutons emplaced along or within regional transpressional shear zones. The new ages are then complemented with a statistical analysis of previously published U–Pb pluton zircon ages from the adjacent units (La Grande, Opinaca, Opatica), which revealed a subtle southward-younging trend (i.e., towards the presumed trench) in otherwise broadly coeval and areally extensive plutonism characterized by diverse compositions. The observed spatiotemporal pattern of plutonism is transitional between unfocused, plume-related magmatic centers and focused, unidirectionally migrating magmatism of modern arcs, perhaps as a result of hotter environment and complex interplay between the waning plume-related regime and increasingly dominating modern-style plate tectonics at the end of Archean.