Geodynamics of the late Archean Wawa Subprovince Greenstone Belts, Superior Province, Canada
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The late Archean (ca. 2.80-2.68 Ga) Schreiber-Hemlo and White River-Dayohessarah greenstone belts of the Superior Province, Canada, are collages of komatiite to tholeiitic, transitional and alkaline basalt ocean plateau sequences; tholeiitic and calc-alkaline basalt to rhyolite volcanic island arc sequences; and arc-derived, syn-kinematic siliciclastic trench turbidites accreted along a SSE-facing convergent plate margin through compressional and transpressional collisions. These subduction-accretion complexes were collectively intruded by the syn-kinematic high-La/Ybn, high-Al, high-Na slab-derived granitoids, syn-kinematic mantle wedge-derived gabbros, and late- to post-kinematic lamprophyres. A rich compositional diversity of komatiites and basalts is present in ocean plateau sequences. The diverse major and trace element compositions of ocean plateau sequences are consistent with a mantle plume that was chemically heterogenous. Mafic to felsic volcanic arc sequences are characterized by coeval tholeiitic and calc-alkaline magma series with variable major and trace element systematics. Both the tholeiitic and calc-alkaline suites were derived from metasomatized subarc mantle wedge sources. Slab melting was a major source of the felsic suite with garnet ± clinopyroxene ± homblende residual in the source. The Schreiber-Hemlo and White River-Dayohessarah greenstone belts have undergone three major phases of deformation. The earliest phase of deformation (D1) is defined by primarily rotated thrust faults: D1 reflects tectonic imbrication of oceanic plateaus, island arcs, and arc-derived turbidites in a subduction-accretion complex. D2 transpression resulted in generation of broken formations and a tectonic melange. The significance of D3 in the study area is thought to be subprovince accretion. The amalgamation processes of the lithotectonic assemblages in the late Archean Schreiber-Hemlo and White River-Dayohessarah greenstone belts are comparable to those of Phanerozoic subduction-accretion complexes, such as the Circum-Pacific, the western north American Cordilleran, and the Altaid orogenic belts, suggesting that subduction-accretion processes significantly contributed to the growth of the continental crust in the late Archean. The episodic growth of the late Archean Superior Province continental crust may have resulted from major plume activities associated with mantle overturn and major orogenies (MOMO).