Abstract

The English River subprovince is one of two metasediment-dominated terranes in the western Superior Province. It has been interpreted as an accretionary complex, a foreland, or a fore-arc basin that developed and was subsequently deformed between the metavolcanic-rich Uchi subprovince and the orthogneiss- and metaplutonic-dominated Winnipeg River subprovince during a prolonged transpressive orogeny. To test these hypotheses, we combined a satellite image, aeromagnetic image, and Lithoprobe reflection seismic profile interpretation with detailed structural mapping to better characterize the internal geometry and significance of structural features in the western part of the subprovince in Ontario. Northward-directed subduction and collision of the Winnipeg River subprovince with the Uchi subprovince at ca. >2713–2698 Ma can account for the deposition of the sedimentary rocks, initial metamorphism, and the main phase of deformation in the subprovince, whereas the subduction of Wabigoon crust generated extensive tonalite magmatism in the Winnipeg River and English River subprovinces during the same period. A period of extension, after the docking of the Winnipeg River and Wabigoon subprovinces at ca. 2698 Ma, punctuated the compressive phases of the orogeny and was responsible for high-grade metamorphism, upward bending of the Moho, and localized deposition of late, coarse, alluvial–fluvial metasedimentary rocks. Renewed compression caused by the docking of the Wawa subprovince at ca. 2689–2684 Ma is likely responsible for a largely unrecognized regional upright folding and faulting event that controls the dominant structural geometry of the subprovince. Late in its tectonic evolution, strain was partitioned into dextral deformation that was strongly domainal and limited to the subprovince margins.

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