Akia terrane

The Akia terrane is a tectonostratigraphic terrane located in the North Atlantic Craton in southern West Greenland.[1] The Akia terrane is bounded to the Southeast by the Eo- to Neo-archaean tectonostratigraphic terranes of the Nuuk region,[2] and to the North by the recently recognised Alanngua Complex, which separates the Akia terrane from the Neoarchaean Tuno terrane.[3] The crust in the Akia terrane formed in two major pulses. The first at ~3.2 Ga, predominantly comprises dioritic gneisses, whereas the second, at ~3.0 Ga comprises a more diverse mix of TTG and dioritic gneisses with enclaves of supracrustal rocks and mafic-ultramafic intrusions.[3][4][5][6] Supracrustal rocks are largely tholeiitic and calc-alkaline amphibolites formed at ~3.07 Ga.[7] The mafic-ultramafic intrusions include peridotite cumulates [8] and a belt of noritic intrusions formed at the same time as the TTG gneisses, the Maniitsoq Norite Belt.[9] Various tectonic settings have been proposed for the 3.0 Ga crust forming event, including subduction related magmatism,[4] stagnant lid tectonic processes,[10] and crust and mantle melting in an ultra-hot orogeny [9]

The terrane underwent high grade granulite facies metamorphism at ~3.0 Ga, immediately after or simultaneous with the second major crust forming event.[9][10] Further high temperature metamorphism followed at ~2.7 Ga and ~2.5 Ga.[3][11] The earlier event is marked by widespread formation of pegmatite granite dykes [6] and may be associated with the juxtaposition of the Akia and Tuno terranes [3][11]