Evolution of an Archean subprovince boundary: a sedimentological and structural study of part of the Wabigoon–Quetico boundary in northern Ontario

Abstract

A prograded clastic wedge, represented by formation- to group-scale units of metasedimentary strata in the Beardmore–Geraldton Terrane, developed in a transitional zone at the southern margin of a volcanic arc between the Onaman–Tashota Terrane, part of the Wabigoon Subprovince to the north, and the Quetico Subprovince, an accretionary prism to the south. Megasequences or couplets with lower basaltic and upper clastic sedimentary parts are now exposed as regionally metamorphosed mafic volcanic and sedimentary belts, outlining thrust slices. Relatively proximal facies (belts) are juxtaposed on top of more distal ones, forming a regional stratigraphy of repetitive volcanic–sedimentary megasequences produced in an imbricate thrust stack. A variety of minor and regional structural features illustrate accretion and subsequent transpression. Isoclinal folding associated with dip-slip, overthrust shearing was followed by inhomogeneous ductile strain of dextral sense along weak lithologies and existing shear zones. Possible subduction-related accretion added a monotonous sequence of arc-derived wacke turbidites to the underside of the thrust-imbricated arc-margin succession. Post-tectonic melting in the northern section of this tectonically thickened accreted sediment gave rise to S-type granites.