THE ACCRETIONARY GROWTH AND REWORKING OF SOUTHEASTERN LAURENTIA THROUGH THE U-PB-HF DETRITAL ZIRCON RECORD: INSIGHTS FROM THE LAC-SAINT-JEAN REGION (CENTRAL GRENVILLE PROVINCE, QUEBEC, CA)

The pre-collisional accretionary evolution of the Grenville Province has been studied the last 30 years using Sm-Nd isotopic mapping of felsic orthogneisses. The fidelity of the Sm-Nd isotopic record can be compromised though by metasomatic processes in high-grade metamorphic terranes leading to spurious inferences about their crustal growth. The perspective of detrital zircon grains from pre-collisional metasedimentary sequences on the crustal evolution of the Grenville Province, using the robust U-Pb and Lu-Hf isotopic couplet, remains poorly explored. In this study, we combine detrital zircon U-Pb and Lu-Hf isotopic data from quartzites of three pre-orogenic supracrustal sequences, named as the Montauban, Wabash, and Barrois complexes, that crop out in the Lac-Saint-Jean region (QC, CA) and show maximum depositional ages of c. 1.45 (Montauban) and c.1.2 Ga (Wabash and Barrois). Detrital zircon grains from the Montauban quartzite exhibit two dominant age peaks at 1463 Ma, and 1617 Ma whereas those from the Wabash and Barrois complexes a dominant age peak at c.1850 Ma. The zircon grains of the 1463 Ma and 1617 Ma age components show dominantly suprachondritic εHf values (εHf > 0) indicating input of detritus from proximal and/or zircon-fertile juvenile sources of Peri-Laurentian origin. The zircon grains of the 1850 Ma age component show a vertical spread in εHf-time space denoting contribution from reworked 2.7 Ga Archean sources of chondritic composition, probably derived from the southern margin of the Superior Province. Overall, the U-Pb-Hf isotopic archive of detrital zircon grains from vestiges of pre-collisional basins in the Grenville Province records Paleo and Mesoproterozoic snapshots on the accretionary growth and reworking of southern Laurentia.