Corundum (ruby) growth during the final assembly of the Archean North Atlantic Craton, southern West Greenland

Abstract We investigate the petrogenesis and tectonic significance of corundum (ruby)-bearing late Neoarchean rocks from the Maniitsoq region of southern West Greenland using petrology, thermobarometry, phase equilibrium modelling, and carbon isotopes as well as U–Pb zircon and rutile geochronology. Corundum was generated by amphibolite-facies metamorphism of an aluminosilicate schist. Thermobarometry and phase equilibrium modelling constrain the P–T conditions of corundum growth to ~ 600–700 °C at ~ 4–7 kbar. The presence of graphite suggests corundum growth in the presence of a mixed hydrous–carbonic fluid; this fluid was responsible for the transfer of SiO2 out of the precursor rock generating quartz-undersaturated conditions that enabled corundum growth. Carbon isotope values of graphite from corundum-bearing schist indicate a biogenic origin and are inconsistent with the fractionation of non-biogenic carbon. Zircon U–Pb geochronology documents regional metamorphism at c. 2.72–2.60 Ga. U–Pb rutile geochronology yields an upper intercept age of c. 2.5 Ga, which is interpreted as the best age estimate of corundum growth. The growth of corundum in southern West Greenland reflects heating associated with post-tectonic magmatism after the assembly of the North Atlantic Craton.