Linked evolution and in situ growth of the Wabigoon superterrane, Superior Craton: evidence from zircon U-Pb isotopes and whole-rock geochemistry

Archaean crustal growth models remain contentious. Isotopically distinct crustal domains in the Superior Craton have been interpreted as exotic terranes, which has bolstered models of Archaean subduction-accretion. However, new geochemistry and geochronology of 3.0-2.7 Ga felsic igneous rocks across the Wabigoon superterrane, Superior Craton, together with a new stratigraphic synthesis, point to a shared chemo-stratigraphy across four isotopically-defined ‘terranes’. Uranium-Pb zircon emplacement ages were measured for 109 new samples by ion microprobe. Two chemical shifts were identified across 3.02–2.68 Ga magmatism. At 2.75 Ga, variability in major oxides increases and some LILE, LREE, Sr/Y and La/Lu increase. At ca. 2.69 Ga, sanukitoid-like rocks record an increase in Mg#, compatible and transition elements, P2O5, LREE and steepening of REE patterns. The 2.75 Ga shift highlights the onset of greater melting/crystallisation depths and changing magma sources, reflecting cratonic thickening. The shift follows ∼2.8 Ga continental emergence recorded in basal conglomerates at a transition from plateau-like to rift- and arc-like greenstone assemblages. The <2.7 Ga shift reflects garnet-stable melting of a metasomatised mantle and correlates with craton-wide sedimentation and orogenesis.Several age peaks in near-continuous Marmion terrane magmatism from 3.02 Ga to 2.78 Ga are contemporaneous with scattered 3.02–2.78 Ga emplacement and inherited zircon ages from the 3.4 Ga Winnipeg River and 2.9 Ga Eastern Wabigoon terranes. All terranes record major magmatic episodes at ca. 2.74-2.72 and 2.7 Ga. A 2.87 Ga zircon xenocryst in the 2.72 Ga Atikwa batholith of the Western Wabigoon terrane is the earliest isotopic evidence for Mesoarchaean basement there. Contemporaneous magmatism, evidence for Mesoarchaean zircon age inheritance in Neoarchaean terranes, and a newly hypothesized time-correlative unconformity across terranes, favours (para-) autochthonous growth of the superterrane. The granite-greenstone record is reconciled by Mesoarchaean rifting, and subsequent development of a Neoarchaean suprasubduction zone before culminating with Kenoran collision. Therefore, <2.78 Ga subduction-accretion overprinted and shortened, but did not necessarily assemble, the Wabigoon superterrane. This finding complements growing global evidence for a unique mechanism of Archaean granite-greenstone development that culminated in late, localized subduction before cratonisation, with implications for the global onset of plate tectonics in the late Archean.