Abstract Numerous supracrustal belts in southern West Greenland host leucoamphibolites, which commonly preserve volcaniclastic textures, and are interpreted as meta-andesites. Such rocks are associated with mesocratic amphibolites of tholeiitic basaltic compositions, which display pillow-lava structures and, thus, support eruption in an oceanic environment. Here we present bulk-rock Lu–Hf isotope data for meta-andesites from the approximately 3071 Ma Qussuk supracrustal belt. Surprisingly, we find evidence for the involvement of a source with near-chondritic Hf-isotope composition in the meta-andesites, whereas the metabasalts display more depleted compositions, with around +4. Trace element modelling indicates that fractional crystallization in combination with crustal assimilation (AFC) is not capable of producing the geochemical compositions of the meta-andesitic rocks from a basaltic melt. Instead, these meta-andesites point to large degrees ( c. 50%) of magma mixing, involving mafic and felsic end members. This may either represent: (1) a magma chamber process; (2) mantle-wedge overprinting by a silicic component; or (3) large degrees of melting of primitive mafic crust. Given that there is abundant independent structural and metamorphic evidence for horizontal tectonics in the Archaean crust of southern West Greenland, it is likely that these calc-alkaline meta-andesites and tholeiitic metabasalts were produced by Mesoarchaean subduction zone volcanism.

Abstract The Archaean North Atlantic Craton underpins much of North America, Greenland and northern Europe, and incorporates the Earth’s oldest extant continental crust. This paper reviews the current understanding of the region’s crustal evolution, and considers our ability to investigate interrelationships between different fragments of the North Atlantic Craton. Detrital zircons from Mesoproterozoic to Cambrian basal sediments in NW Scotland have been re-examined in light of new data from the Archaean Tarbet supracrustal unit and the Palaeoproterozoic Rubha Ruadh granite. Hf model ages are recorded from 4160 to 1410 Ma, peaking at c. 3350 Ma, and are associated with U–Pb crystallization ages from 3670 to 1070 Ma, peaking at c. 2700 and 1700 Ma. The Rubha Ruadh granite is consistent with partial melting of Northern Region basement without contamination by juvenile magmas or supracrustal material, while the Tarbet Supracrustals record a minimum model age of c. 3200 Ma. Each of these units records Hf model ages that imply remelting of Eoarchaean (4000–3600 Ma) crust. Similar distributions of crystallization and model ages have been identified around the North Atlantic Craton, suggesting that Eoarchaean crust was once extensive in the region and constitutes the foundation of both Scotland and the North Atlantic Craton. Supplementary material: All new zircon U–Pb-Hf-O data from this study are available at www.geolsoc.org.uk/SUP18776.