Abstract

We report new U-Pb ages and Sm-Nd isotope data for an Eoarchean volcano-sedimentary sequence in the northeast Superior Province of northern Quebec, Canada. The Nuvvuagittuq supracrustal sequence is characterized by mafic amphibolite rocks with rare felsic schists, accompanied by ultramafic sills, oxide-rich and quartz-rich iron formations, and possible conglomeratic units, with peak metamorphism having reached upper amphibolite facies. The sequence crops out as an open, shallow, south-plunging synform with tonalites in the center and around the exterior margins of the fold structure. A 3817 ± 16 Ma age from a felsic schist is interpreted to represent a maximum age for the sequence, whereas a 3661 ± 4 Ma age from the enclosing tonalites suggests a minimum age. Detrital zircons from a conglomeratic unit yielded similar old ages of ca. 3.78 Ga. Younger ages of ca. 3.66 and 3.3 Ga from a conglomeratic unit and a felsic schist, and 2.7 Ga ages from an amphibolite gabbro and a pegmatite dike, underline the polymetamorphic history of the sequence. Initial Nd isotope compositions (ϵNd3.8 = −0.5 to + 2.3) for mafic amphibolites and felsic schists are indicative of a moderately depleted mantle. Sm-Nd analyses of a 2.7 Ga pegmatite dike and the ca. 3.66 Ga tonalites both yield Nd depleted mantle model ages (TDM) of ca. 3.9 Ga, indicating that they were derived from a crust of juvenile Eoarchean origin. We propose that fragments of Paleoarchean to Eoarchean terranes that rim the Superior Province represent remnants of a larger terrane(s) that was rifted and dismembered prior to the formation of the 3.0–2.7 Ga Superior Craton.

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