The Arrowsmith orogeny: Geochronological and thermobarometric constraints on its extent and tectonic setting in the Rae craton, with implications for pre-Nuna supercontinent reconstruction

Abstract

Geochronological and thermobarometric data for two widely spaced and previously unstudied areas of the Rae craton, Canada provide important temporal and spatial links between previously investigated areas in the northern and southern Rae craton that had been interpreted to have been reworked during the ca. 2.5–2.3Ga Arrowsmith orogeny. On southern Boothia Peninsula, upper amphibolite- to granulite-facies metamorphism, dated by in situ SHRIMP U–Pb analysis of monazite, occurred at ca. 2.64–2.60, 2.54, 2.50–2.49, 2.44, and 2.37–2.34Ga, with retrograde monazite growth at 2.27Ga. SHRIMP U–Pb ages of zircon in two metasedimentary rocks provide a further indication of metamorphism at ca. 2.54 and 2.50Ga, which also corresponds to the age determined for a K-feldspar augen granite. Textural relationships indicate that the regional foliation formed between ca. 2.54Ga and 2.50–2.49Ga. Peak metamorphic conditions of ∼700°C and 5–6kbar are interpreted to have been reached during the 2.37–2.34Ga event. In the McCann–McArthur Lake region of the southwestern Rae craton, upper amphibolite- to granulite-facies metamorphism is dated by in situ SHRIMP monazite ages of ca. 2.53, 2.47, and 2.37–2.28Ga. Textural relationships indicate deformation initiated by ca. 2.37Ga and terminated by ca. 2.30Ga. Metamorphic conditions of ∼5kbar and 700–735°C were quenched at ca. 2.3Ga following peak conditions of ∼7kbar and 800°C.The evidence for regional deformation at 2.54–2.49Ga on southern Boothia Peninsula supports an Andean-type accretionary margin setting for the Arrowsmith orogeny. A collisional event may have terminated high-grade metamorphism in the northern region by ca. 2.34Ga while metamorphism associated with continental arc magmatism continued in the south until at least ca. 2.28Ga. These combined data demonstrate the continuity and broad extent of the Arrowsmith orogen along the western flank of the Rae craton, extending ∼1500km from northern Saskatchewan to northern Baffin Island. The broad extent of this globally rare orogenic event provides an important piercing point for supercontinent reconstructions which are discussed in a companion paper. The inferred convergent tectonic activity between ca. 2.54 and 2.28Ga is interpreted to have occurred on the flank of a growing supercontinent, a setting that could account for an apparent slowdown, but not shutdown in global tectonics.