U–Pb age and Nd isotopic evidence for Archean terrane development and crustal recycling in the south-central Wabigoon subprovince, Canada

Abstract.

U–Pb geochronology is presented for 19 volcanic and associated plutonic rocks from nine greenstone belts within the southern part of the central Wabigoon subprovince (CWS), western Superior Province. Data indicate that early felsic volcanism (3,014–2,999 Ma) was coeval with emplacement of the Marmion batholith at 3,002 Ma. This was followed by periods of mafic volcanism (with minor felsic and komatiitic compositions) between 2,963 and 2,898 Ma across the south-CWS. Plume-driven mafic and komatiitic volcanism occurred in the Lumby Lake and Lac des Mille Lacs belts at ca. 2,828 Ma. Eruption of komatiitic tuffs in the Steep Rock belt at <2,780 Ma was proceeded by more widespread mafic and minor intermediate to felsic volcanism at 2,729–2,726 Ma. Zircon inheritance and Nd isotope data indicate that the CWS south of the Garden Lake belt comprises a juvenile, 3.0 Ga terrane (the Marmion terrane). Subsequent magmatism was ensialic, occurring in a continental, although submerged setting. Recycling of the 3.0 Ga Marmion basement during successive volcanic events, although somewhat cryptic, was widespread and represents a significant Archean process. 2,726 Ma rhyolite in the Garden Lake belt has a 3.22 Ga Nd model age and lies at the southern boundary of the distinct north-CWS, which has a 3.3–3.2 Ga crustal prehistory. The north-CWS may represent a heavily reworked extension of the adjacent 3.3 Ga Winnipeg River subprovince and was probably separate from the Marmion terrane at 3.0 Ga. These two recycled terranes differ significantly from the juvenile, Neoarchean, volcanic-dominated western Wabigoon. Although the boundaries between these terranes are in most places cryptic, they may indeed represent suture zones which were fundamental to the development of the Wabigoon subprovince.