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

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. 2.5–2.3 Ga 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 2.37–2.34 Ga, with retrograde monazite growth at 2.27 Ga. SHRIMP U–Pb ages of zircon in two metasedimentary rocks provide a further indication of metamorphism at ca. 2.54 and 2.50 Ga, which also corresponds to the age determined for a K-feldspar augen granite. Textural relationships indicate that the regional foliation formed between ca. 2.54 Ga and 2.50–2.49 Ga. Peak metamorphic conditions of ∼700 °C and 5–6 kbar are interpreted to have been reached during the 2.37–2.34 Ga 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 2.37–2.28 Ga. Textural relationships indicate deformation initiated by ca. 2.37 Ga and terminated by ca. 2.30 Ga. Metamorphic conditions of ∼5 kbar and 700–735 °C were quenched at ca. 2.3 Ga following peak conditions of ∼7 kbar and 800 °C.The evidence for regional deformation at 2.54–2.49 Ga 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. 2.34 Ga while metamorphism associated with continental arc magmatism continued in the south until at least ca. 2.28 Ga. These combined data demonstrate the continuity and broad extent of the Arrowsmith orogen along the western flank of the Rae craton, extending ∼1500 km 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 2.28 Ga 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.

► First geochronological and thermobarometric data for southern Boothia Peninsula (SBP), north-central Rae craton.
► First geochronological and thermobarometric data for McCann–McArthur Lake region (MMLR), southwestern Rae craton.
► ca. 2.54–2.49 Ga deformation in SBP suggests convergent, followed by arc rift setting.
► Inferred 2000 km long extent of ca. 2.54–2.27 Ga orogen provides piercing points for supercontinent reconstruction.
► Convergent tectonics and crustal addition at 2.4–2.27 Ga argues against global plate tectonic shutdown at that time.