The diversity of sources of late Archean granites reflects a transition from plume-dominated to plate tectonics in the Superior Province, Canada
Abstract
The Superior Province in Canada represents an excellent natural laboratory to test various models of crustal growth and evaluate tectonic regimes during the late Archean. Here, we present new geochemical and geochronological data for ca.
2.8-2.7 Ga plutons intruding different lithotectonic units of the north-eastern part of the Superior Province that demonstrate a complex nature and evolution of magma sources in relation to a changing tectonic setting. Four distinct plutonic suites were newly identified: (1) sodic tonalite-diorite (TD) with a composition resembling low-pressure TTG-like melts, (2) sodic tonalite-granodiorite-diorite (TGD) with medium/high-pressure TTG-like signatures, (3) Mg-K-rich monzogranite to monzodiorite (sanukitoids; MMD), and (4) K-rich granodiorite-granite-monzogranite (GGM). These suites are interpreted as recording a temporal evolution from plume-assisted melting of lower mafic continental crust through melting of a subducted oceanic slab at different depths to large-scale re-melting of the previously formed and amalgamated crustal units. In this evolutionary scheme, the approx. 2730-2700 Ma subduction-related plutonism is the most voluminous addition of the juvenile arc material and thus represents the most significant crustal growth event. Altogether, the above inferences and published data suggest that the late Archean plutonism in the Superior Province formed during a transitional regime from plume-dominated to plate-tectonic over a short time span between approx 2730 and approx. 2700 Ma and that this transition was markedly diachronous across the Province.