GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 204-6
Presentation Time: 9:30 AM


HENRIQUE-PINTO, Renato, Département de géologie et de génie géologique, Université Laval, 1065, av. de la Médecine, bureau 4309, Québec, QC G1V 0A6, Canada, GUILMETTE, Carl, Department of geology and geological engineering, Laval University, Quebec city, QC G1X3T9, Canada, MCNICOLL, Vicki, NRCAN-RNCAN, Natural Resources Canada, 601 Booth Street, 6th Floor, Room: 692, Ottwa, ON K1A 0E8, Canada, BILODEAU, Carl, Renseignements généraux, Ministère de l’Énergie et Ressources Naturelles du Québec, 5700, 4e Avenue Ouest, A 409, Quebec, QC G1H 6R1, Canada and CORRIGAN, David, Geological Survey of Canada, Central Canada Division, 497-601 Booth St., Ottawa, ON K1A 0E8, Canada,

The New Quebec Orogen (NQO) is a Paleo-Proterozoic supra-crustal belt that underwent reworking when the Superior Craton collided with the Core Zone, during the Trans-Hudson Orogeny. Within the NQO, the Labrador Trough regroups greenschist-facies sedimentary and volcanic sequences (Kaniapiskau Supergroup) inferred to represent the rifted margin of the Superior and a potential oceanic domain, whereas the Laporte Group, composed of similar successions but metamorphosed to higher grades, remains of unclear origin. Competing models purport that the Laporte Group is either a deeper, higher grade exposure of the Labrador Trough, or an exotic terrane. Large scale sampling, petrography and U-Pb detrital zircon geochronology provide insights to elucidate the sedimentary provenance and depositional environments for both zones.

New results reveal a different sedimentary architecture for both units. In particular, the majority of metarenites from Kaniapiskau Supergroup have medium to high textural and compositional maturity, such as meta-quartzarenites and meta-subarkoses; whereas the metarenites from Laporte Group suggest photoliths with low to medium textural/compositional maturity, like feldspathic and some lithic meta-wackes.

A total of 343 zircon analyses from the Kaniapiskau Supergroup yield ages older than 2.5 Ga (2565 ±12 Ma, youngest zircon), with typical Archean Superior-type signature as the main source area and a main statistical age peak at 2722 Ma. There is more than a 150 Ma gap between detrital zircon ages and the interpreted depositional age, suggesting a divergent environment like a rifted and/or passive margin.

In contrast, detrital zircons from the Laporte Group (a total of 234 analyses) yield ages older than 1.8 Ga, with the youngest zircon dated at 1827 ± 25 Ma and a dominant statistical age peak at 1843 Ma. Metamorphic monazite ages from Laporte Group previously dated at 1793 ± 2 Ma suggest a relative short depositional time period (around 40 Ma). The presence of detrital zircon age peaks at 2.2- 2.4 Ga suggests an exotic terrain compatible with the Core Zone as the main source area. The presence of the orogenic-type De Pas Batholith suggests eastward subduction at 1840-1830 Ma and the time period between detrital ages and deposition may represent a transition between forearc to foreland basin.