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The Steep Rock Group, Little Falls assemblage, Finlayson greenstone belt, and Lumby Lake greenstone belt form a once-continuous Mesoarchean terrane at the southern margin of Wabigoon subprovince, Canadian Shield. Synchronous with eruptive activity, oceanic plateau basalts in this region were intruded by tonalitic batholiths, which fed intermediate to felsic volcanic cones and associated mass-flow sediment aprons. A sedimentary succession capping the volcanic pile records stream-induced channel incision into upraised basalt and tonalite, feeding sediment to a delta complex. Base-level rise caused the incised channels to backfill, stromatolitic carbonates to develop in shallow-marine areas, and finally, deposition of iron formation to dominate. A Mesoarchean terrane was also examined in the Wallace Lake area of Manitoba. Here a kilometer-thick, transgressive succession records a transition from fluvial to delta-front to prodelta turbiditic environments, with eventual drowning and siliciclastic sediment starvation leading to dominance by carbonate and iron formation deposition. Sedimentary rocks that cap the oceanic Cretaceous to Holocene Kerguelen Plateau are a direct analogue for the depositional environments, sediment source rocks, and drowning events that define the stratigraphy of the Mesoarchean successions studied here. The Steep Rock–Lumby oceanic plateau formed and actively grew during an interval of 230 m.y. This sequence produces serious problems for Mesoarchean tectonic models in which increased heat dissipation produces fast spreading or numerous spreading ridges. A Mesoarchean, mantle plume–dominated heat dissipation process is in much better agreement with the data presented here.

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