Assembly of Archean cratonic mantle lithosphere and crust: plume–arc interaction in the Abitibi–Wawa subduction–accretion complex

Recent thermodynamic models suggest that direct interaction between mantle plumes and island arcs will enhance long-term arc buoyancy and contribute disproportionately to the crustal record. However, crustal growth models have also proposed a range of differing mechanisms for Archean crust formation that emphasize specific rock types, such as tonalite–trondhjemite–granodiorite (TTG) plutons or high magnesian andesites. Studies in the Abitibi–Wawa subprovince, allow these proposals to be evaluated in the context of the worldʹs largest greenstone belt. Crustal growth in the southern Superior Province was the product of subduction–accretion tectonics enhanced and modified by mantle plume processes, particularly mantle plume–island arc interaction. High Archean geothermal gradients promoted volumetrically minor slab melts from the earliest phases of the Abitibi–Wawa arc, resulting in the adakite–high magnesium andesite–Niobium–enriched basalt association. However, recent flat subduction models for the formation of adakites also provide important insights into the generation of syn-tectonic Archean TTG batholiths that were probably derived from subducted, rather than accreted, oceanic crust. The distribution of Niobium enriched basalts (NEB) in the southern Superior Province may reflect plume controlled shallow subduction beneath the Abitibi belt that limited melting depths within a restricted asthensopheric mantle tongue. A well-constrained tectonic history, the mantle source requirements of successively-formed components of the Abitibi–Wawa crust, and detailed seismic interpretations of crustal architecture all preclude the presence of an autochthonous mantle lithospheric root beneath the Abitibi–Wawa arc. Instead, the late diapiric ascent of buoyant refractory plume residue and subducted oceanic crust resulted in the coupling of the mantle root and arc crust 10ʹs of million years following batholith emplacement. High-velocity material identified at the base of the crust and centered beneath the Abitibi–Pontiac suture zone is probably Archean aged rather than Proterozoic. It corresponds to minor melts generated during ascent of the plume residue diapir and underplated prior to and during formation of the >200 km thick Abitibi–Wawa continental mantle lithosphere root.