Isotopic constraints on the architecture and early (ca. 2.4–2.3 Ga) Paleoproterozoic evolution of the northwestern Rae craton, Canada

Abstract

Queen Maud block (QMb) is re-defined as an area of dominantly Mesoarchean crust forming the northwestern part of the Rae craton. Four U-Pb zircon age determinations (ca. 3.3–2.97 Ga) extend QMb ∼40 km farther west than previously known to a major tectonic boundary marked by a >450 km-long belt of ca. 1.9 Ga peraluminous leucogranite in the Thelon tectonic zone. Crust older than 3.3 Ga is indicated by inherited zircon up to 3.95 Ga in one sample. The absence within QMb of 2.6 Ga plutonic rocks, a dominant component of the central Rae craton, suggests distinct Neoarchean tectonic histories and separation of these crustal blocks prior to accretion of ca. 2.56–2.51 Ga Boothia terrane, stitching by ca. 2.5 Ga Queen Maud granitoids and a shared post-2.5 Ga history.

Tonalite dated at 2.41 Ga in QMb and monzogranite dated at 2.34 Ga in the adjacent Thelon tectonic zone have geochemical characteristics of convergent plate margin magmatism (arc ± slab-failure). Similarity in the Nd isotopic compositions of 2.34 Ga Thelon monzogranite and ca. 2.3 Ga plutonic rocks in Buffalo Head terrane, as well as 2.07 Ga and 2.0 Ga plutonic rocks in both regions point to a similar Neoarchean basement component. This basement terrane is proposed to have collided with the Rae at ca. 2.41 Ga and driven ca. 2.4–2.3 Ga tectonometamorphism during the Arrowsmith Orogeny.

The western Rae represented a convergent margin at 2.41–2.3 Ga and potentially 2.6–2.5 Ga, the latter broadly synchronous with the MacQuoid orogeny on the southeastern Rae margin. Throughout this time period, the central Rae craton was in an upper-plate position. Sustained mantle downwelling driving plate convergence towards the central Rae craton, as previously recognized at 2.0–1.9 Ga, was maintained from the Neoarchean through multiple Paleoproterozic orogenies (Arrowsmith, Taltson-Thelon and Hudsonian), establishing the Rae craton as the nucleus of proto-Laurentia within the Nuna supercontinent.