Stephen J. Mojzsis
The Inukjuak domain in the northwestern Superior Province of Canada hosts numerous supracrustal belts that occur as km-scale enclaves in Archean granitoid gneisses. The Eoarchean (ca. 3750-3780 Ma) Nuvvuagittuq Supracrustal Belt (NSB) in northern Québec is the best known of these variably metamorphosed and deformed volcano-sedimentary (supracrustal) units. These Innucsuac Complex supracrustals are dominantly amphibolitic, and are surrounded and/or intruded by several generations of granitoid gneisses of tonalite-trondhjemite-granodiorite (TTG) composition. Few detailed geochronology studies for the assorted Inukjuak domain gneisses and the associated enclaves have been performed. 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 (Aboi), 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 various gneisses as well as from a little-studied, locally significant gneiss (the Voizel suite; Avoi). Results show that a tonalitic gneiss at the center of the NSB fold belt (Central Tonalitic Gneiss; CTG) preserves mainly ca. 3650 Ma zircon cores. Outside the NSB, the previously undated 3550 Ma Avoi that was thought to be contemporaneous with the CTG is instead about 100 Myr younger. Aboi rocks contain inherited zircon cores up to 3700 Ma with ca. 2700 Ma rim overgrowths. A tonalitic gniess that transects a large unnamed supracrustal belt northeast of the NSB (within Avoi), yielded a maximum concordant zircon age of 3653±8 Ma.
Greer, Jennika, "Multiple generations of granitoid gneisses hosting supracrustal belts in the Archean Inukjuak domain (Quebec, Canada)" (2013). Undergraduate Honors Theses. 540.