Convergent margin tectonics, central Wabigoon subprovince, Superior Province, Canada

Abstract

Best known for its Neoarchean greenstone-granite terranes in the east and west, the Wabigoon subprovince of the Superior Province features a central transverse corridor of Meso- and Neoarchean gneissic, granitoid, and minor supracrustal rocks resembling an eroded intermontane plateau. Structural analysis and U–Pb geochronology in the north-central Wabigoon subprovince reveal a complex history of plutonism, supracrustal rock deposition, polyphase deformation and amphibolite-facies metamorphism between 3075 and 2670 Ma. The geometric and kinematic character of D 1 and D 2 deformational events recorded in 2890–2718 Ma tonalitic gneisses remain cryptic as a result of magmatic and structural (D 3–5) overprinting, but the early structures are bracketed in age between 2725 and 2713 Ma by a polydeformed gneiss and tonalite dyke. These events occurred deep within an active continental magmatic arc and correspond in age to a collision between the juvenile Wabigoon and continental Winnipeg River subprovinces recognized to the west. Clastic sediments deposited after 2701 Ma are the youngest rocks involved in subsequent regional deformation. A D 3 event is responsible for rapid burial of supracrustal units to 15 km within warm arc crust, and imposition of a regional, penetrative, S 3 foliation that accommodated some relative uplift prior to 2697 Ma, the age of a discordant granodiorite dyke. This event corresponds to variably preserved, steep, north-trending D 1 structures recognized in adjacent greenstone belts. Subsequent (D 4) ductile deformation defines the map pattern in the deep crustal rocks of the central Wabigoon subprovince. Upright, east-trending F 4 folds developed synchronously with D 2 dextral transpressive structures that formed throughout the Wabigoon subprovince prior to 2698 Ma. The final (D 5) sinistral shearing event occurred during emplacement of mantle-derived granodiorites of sanukitoid affinity (2688 Ma) and crust-derived granites (2685 Ma). This event appears to have triggered rapid cooling, reflected in 2680–2670 Ma titanite dates and late brittle increments of displacement.