Reduced, reused and recycled: Detrital zircons define a maximum age for the Eoarchean (ca. 3750-3780 Ma) Nuvvuagittuq Supracrustal Belt, Quebec (Canada)

A key discovery from the Hadean (pre-3850 Ma) detrital zircon record has been that the dichotomy of granitic and basaltic crust was established within about 160 Myr of Earth's formation (Harrison, 2009). Understanding the origin and fate of this primordial crust would greatly add to what we know about the geodynamics of the Hadean Earth. Insights emerge from Sm-147,Sm-146-Nd-143,Nd-142 isotope data reported from different Eoarchean terranes worldwide, including the Nuvvuagittuq Supracrustal Belt (NSB) in northern Quebec. Some Ca-poor (cummingtonite-rich) amphibolites and granitoid gneisses of the NSB preserve lower Nd-142/Nd-144 than Bulk Silicate Earth (BSE); these also show positive correlations against Sm-147/Nd-144 that were used by O'Neil et al. (2008, 2012) to assign a ca. 4400 Ma age. Alternatively, the compositions were inherited during the formation of the NSB at around 3800 Ma (Roth et al., 2013; Guitreau et al., 2013). To resolve this discrepancy, ion microprobe U-Pb ages are reported for detrital zircons from NSB meta-sediments from within the same supracrustal successions that preserve low Nd-142/Nd-144. The youngest detrital zircon cores of igneous derivation define a maximum age for the NSB of ca. 3780 Ma. This age is about 600 Myr younger than that obtained from Nd-142/Nd-144 vs. Sm-147-Nd-143 regressions. Thus, just like the variable Nd-142/Nd-144 ratios reported for other Eoarchean terranes, non-BSE Nd-142/Nd-144 values of the NSB were inherited from an older component. (C) 2012 Elsevier B.V. All rights reserved.