The Tuno terrane and evolution of the northernmost part of the North Atlantic Archean Craton, West Greenland

• The Tuno terrane forms the north of the Archean craton, West Greenland. • The Tuno terrane is dominated by 2760–2730 Ma plutonic protoliths, with minor older components. • The Tuno terrane is a lateral continuation of the Tasiusarsuaq terrane farther south in Greenland. • From ∼ 2720 Ma, the Tuno-Tasiusarsuaq terrane(s) collisional orogeny amalgamated them with Meso- and Eoarchean terranes in the Isua-Nuuk region. The northern edge of the North Atlantic Craton in West Greenland comprises ∼ 24,000 km 2 of amphibolite-granulite facies gneisses. South of this is a belt of diverse gneisses affected by Neoarchean metamorphism and deformation known as the Alanngua Complex ( Steenfelt et al., 2021 ), followed by the Akia terrane, that is dominated by 3250–3180 Ma and 3070–2970 Ma gneisses. Using both published and new U-Pb zircon ages (44 samples) and zircon Lu-Hf isotopic compositions (21 samples) from Archean gneisses combined with U-Pb-Hf detrital zircon data from Holocene stream sediments, we demonstrate that the entire section of the craton north of Søndre Isortoq is within the Tuno terrane as first defined by Friend and Nutman (1994) . Diagnostic of the Tuno terrane is 2770–2750 Ma magmatism followed at 2740–2730 Ma by more magmatism and metamorphism up to granulite facies. However, within the Tuno terrane there are scattered older components (most commonly 2860–2800 Ma). Also present are minor amounts of ∼ 3100–3000 Ma gneisses, the early Archean Ukaleq gneiss complex ( Rosing et al., 2001 ) and the Qarliit Tasersuat assemblage ( Nutman et al., 2004a ). Exposed 180 km to the south of the Tuno terrane, is the northern edge of the Tasiusarsuaq terrane (bounded on its north side by the folded and metamorphosed ∼ 2710 Ma Qarliit Nunaat Thrust). The Tasiusarsuaq terrane is dominated by 2860–2800 Ma gneisses, with rare enclaves of Eoarchean rocks, and some complex Mesoarchean gneisses intruded by ∼ 2730 Ma granites. Thus, events and lithological components of the Tuno terrane match those in the Tasiusarsuaq terrane south of the Nuuk region, albeit ages and lithological proportions vary. For ∼ 180 km, Tuno and Tasiusarsuaq terrane exposures are separated by the Greenland Ice Sheet. Detrital zircons in modern sediments collected along the intervening ice front show a Tasiusarsuaq + Tuno Mesoarchean and early Neoarchean age signature. Therefore, the Tasiusarsuaq and Tuno terranes are considered lateral variants of a single extensive terrane, which in the Neoarchean (starting from ∼ 2720 Ma) was tectonically juxtaposed against the Mesoarchean Akia − Kapisilik terranes plus the Eoarchean Itsaq Gneiss Complex of the Nuuk region. In this interpretation, orthogneisses of the Alanngua Complex is dominated by the reworked northern margin of the Akia terrane, juxtaposed against the Tuno terrane to the north. After terrane assembly, there was Neoarchean folding and then at 2560–2530 Ma further disruption by faults.