Is the late Archean Superior Province, Canada, the oldest orocline on Earth?

• Four distinct deformational fabrics were detected in the Archean Superior Province. • The fabrics are interpreted as recording oroclinal crustal buckling. • Magnetic fabrics suggest vertical crustal stretching associated with the buckling. • The orocline recorded min. 540 km of horizontal displacement at a rate of 2.9 cm/y. • The ‘Superior’ orocline marks assembly of the late Archean Superia supercraton. The mechanisms and timing of the onset of modern-style plate tectonics and the origin of the supercontinent cycle have been a matter of vigorous debate, especially during the last decade. Plate tectonics requires large-magnitude horizontal motions of lithospheric plates, which have been challenging to reconstruct as the paleomagnetic record from the Archean terrains is prone to remagnetization and contractional structures may form even in a diapiric setting. Here we document a crustal-scale structural pattern and deformational sequence in the Superior Province, the largest Archean craton on Earth, interpreted as recording oroclinal buckling of a TTG-dominated La Grande ribbon terrane during and after its accretion to the inboard Hudson Bay terrane at ca. 2685–2666 Ma. The oroclinal buckling may have been facilitated by the overall high heat flow and thus weak crustal rheologies, typical for the Neoarchean, and progressed from north to south as did the granitic plutonism and siliciclastic deposition in outward-younging Opinaca–Nemiscau marine basins. We explain this buckling as resulting from impingement by the Abitibi greenstone belt, forming an outboard, relatively rigid block of thickened crust that likely jammed the subduction zone. Based on the line-length restoration, the orocline recorded at least 540 km of horizontal displacement and 44% horizontal shortening during a time span of ca. 19 Myr, which would correspond to a displacement rate of ∼2.9 cm/yr. On a global scale, the presumed ‘Superior’ orocline may be viewed as an early stage of plate convergence to form the Superia supercraton at the end of the Archean and is thus the oldest of its kind that has been documented so far.