ACCRETION OR STAGNATION? ARCHEAN GRANULITE-FACIES METAMORPHISM IN THE AKIA TERRANE, WEST GREENLAND (Invited Presentation)

Different paradigms exist for Archean growth and differentiation of continental crust, ranging from horizontal tectonics with subduction zones to vertical tectonics with foundering of greenstone sequences. The Mesoarchean Akia Terrane of the North Atlantic craton represents one the largest exposures of deep crustal Archean granulites found on Earth and provides key insights to Archean orogenic processes. U–Pb zircon geochronology, field relationships, isotope geochemistry, and P–T constraints from the Akia Terrane of the North Atlantic Craton in West Greenland are indicative of two high-temperature metamorphic events at 3.0 Ga and 2.9–2.7 Ga. The Mesoarchean (3.0 Ga) event was associated with temperatures of >800°C at <0.9 GPa and partial melting occurred in the absence of pervasive ductile deformation indicated by nebulitic and undeformed pyroxene-bearing leucosomes in metabasites. The later high-temperature event (2.9–2.7 Ga) reached 820–850°C at 0.8–1.0 GPa and was associated with pervasive ductile deformation of the overlying supracrustal carapace. These two high-temperature metamorphic events are interpreted to reflect a transition in the Akia Terrane from a dominantly vertical tectonic mode in the Mesoarchean, near coeval with sediment deposition, to subsequent widespread Neoarchean compressional tectonism and accretion in the North Atlantic Craton.