ZIRCON PETROCHRONOLOGY OF FERROAN METAPLUTONIC ROCKS ASSOCIATED WITH THE LAC-SAINT-JEAN ANORTHOSITIC SUITE (CENTRAL GRENVILLE PROVINCE, QC, CA): TECTONIC AND PETROGENETIC IMPLICATIONS

The perspective of zircon (ZrSiO₄) on the petrogenetic history of metaplutonic rocks associated with the largest anorthositic suite on the planet, the Lac-Saint-Jean anorthositic suite (QC, CA), remains poorly explored. Adopting a petrochronological approach, we conducted a U-Pb-Hf ± REE isotope study of magmatic zircon grains from ferroan metaplutonic bodies with main aim to better constrain the sources, petrogenesis, and tectonic setting of ferroan magmatism in the Central Grenville Province (Lac-Saint-Jean region, QC, CA). The selected samples are mangerites (n = 8), charnockites (n = 4), and rapakivi granites (n = 1) that border anorthositic plutons and are associated with different pulses of AMCG (Anorthosite-Mangerite-Charnockite-Granite) magmatism in the area. Zircon grains with magmatic textural features from mangerites and charnockites that fall in the ca. 1000 to 1065 Ma age range show Yb/Gd < 25 and εΗf values that vary from -2 ± 0.4 to +2.51 ± 0.57 (2s) indicating the mixing of mantle-derived and crustal components. Zircon grains from rapakivi granites and charnockites that record AMCG pulses at ca. 1169 Ma and 1360 Ma show Yb/Gd > 35 and suprachondritic εHf values that vary from +3.88 ± 0.55 (2s) to +6.84 ± 0.62 (2s) denoting dominantly juvenile magmatic additions. The two-stage depleted mantle Hf model ages of the analysed zircon grains varies from 1.44 Ga to 1.93 Ga with 76 % of the analyses falling in the 1.4 - 1.7 Ga age range. Conclusively, the difference in zircon Yb/Gd ratios and Hf isotope signatures possibly indicate the melting, at different crustal levels, of juvenile and reworked sources associated with the pre-collisional accretionary growth of southeastern Laurentia.