DEVELOPMENT OF PLATE TECTONICS IN AND STABILIZATION OF THE WESTERN SUPERIOR CRATON

The Archean is considered as a pivotal era during the Earth’s evolution in terms of cratonization and development of plate tectonics. The associated geodynamic processes are critical for understanding the evolution of Earth’s lithosphere. This study focuses on the greenstone-dominated western Wabigoon terrane (WWT) and the tonalite-trondhjemite-granodiorite-dominated Winnipeg River terrane (WRT) of the western Superior craton. New seismic, magnetotelluric, and geologic data along with previously published seismic reflections revealed the 3D crustal structures underlying the region; U-Pb geochronology, geochemistry, and zircon Lu-Hf of basement xenoliths in Neoarchean plutons reveal episodic magmatic events from the Meso- to Neoarchean associated with crustal growth (partial melting of mantle) or reworking (partial melting of crust). The crustal structures are consistent with a Neoarchean convergent belt and characterized by an allochthonous greenstone belt as a thrust sheet in the upper crust, a collision zone in the mid- to lower-crust, an apparent crustal root of 3‒5 km relief, and subcreted crustal rocks beneath a mantle wedge. The basement xenolith data show magmatism at ~3060 and ~2930‒2920 Ma that represents reworking of the isotopically evolved components of the incipient WRT at shallow depths, magmatism at ~2910 Ma that records formation of new juvenile magmas and the first reworking of existing juvenile crust, and magmatism at ~2830‒2800, 2735‒2730, and ~2700 Ma that largely reflects reworking of the juvenile components of the incipient WRT at medium to shallow depths prior to the ~2700 Ma trans-crustal magmatism associated with the convergence between the WRT and WWT as shown by the 3D crustal structures. This study proposes that the western Superior craton underwent significant mantle depletion at ~2910 Ma beneath the WRT, which resulted in a more stable lithospheric mantle that facilitated the development of plate tectonics in the western Superior. Progressively, plate tectonics matured around 2700 Ma in the region as shown by the subduction of WWT and collision of WRT. This study also suggests that crustal growth and mantle depletion bracketed by prolonged, episodic crustal reworking may be a fundamental characteristic of cratonization.