Paper No. 48-6
Presentation Time: 3:30 PM
COMBINED ZIRCON MINERAL CHEMISTRY AND U-PB GEOCHRONOLOGY OF ARCHEAN GRANITOID GNEISSES AND SUPRACRUSTAL ENCLAVES OF THE SOUTHERN INUKJUAK DOMAIN, QUEBEC (CANADA)
The Inukjuak domain in northern Québec is part of the Archean Minto Block in the northwestern Superior Province of Canada, and hosts numerous sub-meter to km-scale enclaves of volcano-sedimentary origin (supracrustal rocks, s.l.). These enclaves are locked within diverse and variably-deformed granitoid gneisses of uncertain ages. The Eoarchean (ca. 3750-3780 Ma) Nuvvuagittuq supracrustal belt (NSB) is the best documented of these supracrustal enclaves. Overall, the Innucsuac Complex supracrustals are dominantly amphibolitic, and are surrounded and intruded by several generations of tonalitic-trondhjemite-granodiorite (TTG) and granite (s.s.) gneisses. Few detailed geochronology studies for the assorted Inukjuak domain gneisses and the associated enclaves have been performed beyond the Nuvvuagittuq locality. A tonalitic gneiss at the margin of the NSB fold belt was previously assigned a ca. 3650 Ma age, and granitoid gneisses of the surrounding Boizard suite were considered to have formed at about 2700 Ma. We report new major-, minor- and trace-element geochemistry coupled with U-Pb zircon geochronological data for these gneisses as well as from the volumetrically significant Voizel suite. Results show that at the center of the NSB fold belt, the Central Tonalitic Gneiss (CTG) preserves mainly ca. 3650 Ma zircon cores. Outside the NSB, previously undated 3550 Ma Voizel suite rocks – previously considered contemporaneous with the CTG – are instead about 100 Myr younger. The Boizard suite contains inherited zircon cores up to ca. 3700 Ma with ca. 2700 Ma mantles. A tonalitic gneiss that transects a highly deformed supracrustal belt northeast of the NSB and within the Voizel yielded maximum concordant zircon ages of 3653 ± 8 Ma. Another granitoid gneiss west of the NSB fold belt yielded ages of ca. 3760 Ma. The discovery of Eoarchean rocks throughout the southern Inukjuak domain (>>100 km2) underscores the widespread occurrence of crust of this age well beyond the ~8 km2 confines of the Nuvvuagittuq belt.