Basement terrane correlations and crustal recycling in the western Superior Province: Nd isotopic character of granitoid and felsic volcanic rocks in the Wabigoon subprovince, N. Ontario, Canada

Abstract

The western Superior Province represents a collage of Mesoarchean continental (3.2–2.8 Ga) and Neoarchean continental, arc and oceanic (2.8–2.66 Ga) crustal fragments. Nd isotope data presented here for 89 felsic volcanic and plutonic rocks have been combined with compiled data to generate a data set of over 240 analyses from the Wabigoon and Winnipeg River subprovinces. These samples, from both oceanic and continental environments have been used as crustal probes, their Nd isotopic character used to investigate the extent of basement terranes, the ancestry of crustal fragments, their interaction with each other, and the degree of sialic crustal reworking. The Wabigoon and Winnipeg River subprovinces include three isotopically distinct terranes: (1) The Winnipeg River terrane comprises the Winnipeg River subprovince, the north-central Wabigoon, and the north-eastern Wabigoon subprovince. This region is dominated by Neoarchean granitoid rocks with Mesoarchean vestiges of <3.32 Ga. Numerous Nd model ages, significantly older than 3.0 and 3.39 Ga zircon inheritance, indicate that rocks from this terrane have variably incorporated circa 3.4 Ga basement. (2) The Marmion terrane comprises the south-central Wabigoon subprovince and contains juvenile 3.0 Ga crust (the extensive Marmion batholith). Younger Mesoarchean (2.99–2.80 Ga), and Neoarchean volcanic and plutonic rocks are dominated by 3.0–2.8 Ga Nd model ages which, combined with 3.0 Ga zircon inheritance indicates that they have reworked parts of the Marmion batholith. The south-eastern Wabigoon subprovince, dominated by Neoarchean rocks with 2.9–2.8 Ga Nd model ages may represent a reworked extension of the Marmion terrane. (3) The western Wabigoon terrane comprises the western part of the Wabigoon subprovince. It consists of Neoarchean rocks with predominant 2.8–2.7 Ga Nd model ages indicating crust derived from depleted mantle sources in an oceanic setting. The exceptions are <2.71 Ga rocks near the northern and eastern margins which show evidence for interaction with Mesoarchean basement. Previous workers have suggested that the boundary between the western Wabigoon and Winnipeg River terranes represents a cryptic suture resulting from a collision at circa 2.71 Ga. The boundary between the western Wabigoon and Marmion terranes, although obscured by late intrusions, may be a continuation of this suture zone. The boundary between the Winnipeg River and Marmion terranes in the central Wabigoon is also cryptic. Isotopic data suggest that the Marmion terrane is allochthonous with respect to the Winnipeg River terrane. Common magmatism in these two terranes at 2.93–2.87 Ga suggests that they may have collided during this time. In the eastern Wabigoon subprovince this collision zone is speculated to occur at the Humboldt Bay high strain zone. A complex history of crustal recycling throughout the Mesoarchean and Neoarchean is revealed, which demonstrates the importance of autochthonous development of granite–greenstone terranes in a continental environment. The data also support models of tectonic accretion during the Archean, indicated by the presence of granite–greenstone terranes of allochthonous origin.