EOARCHEAN. TO NEOARCHEAN EVOLUTION OF THE NUVVUAGITTUQ SUPRACRUSTAL BELT: NEW INSIGHTS FROM U-Pb ZIRCON GEOCHRONOLOGY

The Nuvvuagittuq Supracrustal belt in northern Quebec is a rare similar to 9 km(2) fragment of the Earth's early crust. The belt contains a metamorphosed volcano-sedimentary sequence that is at least Eoarchean in age, including amphibolites of the Ujaraaluk Unit that may have protoliths as ancient as 4400 million years old (Ma; O'Neil and others, 2012). Upper amphibolite facies metamorphism and high-strain deformation have obscured many primary field relationships and disturbed whole-rock isotope systematics, leading to debate over the interpretation of previous geochronological data. We report new SHRIMP U-Pb isotopic analyses of zircons from key meta-igneous and newly identified metasedimentary units of the belt. The analyzed samples fall into four categories: (a) felsic gneisses, including sheets interlayered with the supracrustal assemblage and a tonalitic orthogneiss at the margin of the belt; (b) a newly identified metasedimentary unit; (c) fuchsite-bearing quartz-rich layers; (d) mafic gneisses, including a garnet-biotite amphibolite from the Ujaraaluk Unit and a meta-gabbro. The felsic lithologies place constraints on the minimum age of the supracrustal assemblage; oscillatory-zoned zircons separated from a felsic orthogneiss sheet form a discordant array with an upper intercept age of 3774 +/- 32 Ma, and the tonalitic orthogneiss yielded oscillatory zoned zircons with an upper intercept age of 3781 +/- 11 Ma.