Petrogenesis of the Nashwaak Granite, West-Central New Brunswick, Canada: Evidence from Trace Elements, O and Hf Isotopes of Zircon, and O Isotopes of Quartz

The petrogenesis of the Pridoli to Early Lochkovian granites in the Miramichi Highlands of New Brunswick, Canada, is controversial. This study focuses on the Pridoli Nashwaak Granite (biotite granite and two-mica granite). In situ trace elements and O and Hf isotopes in zircon, coupled with O isotopes in quartz, are used to reveal its magmatic sources and evolution processes. In the biotite granite, inherited zircon cores have broadly homogenous δ18OZrc ranging from +6.7‰ to 7.4‰, whereas magmatic zircon rims have δ18OZrc of +6.3‰ to 7.2‰ and εHf(t) of −0.39 to −5.10. The Hf and Yb/Gd increase with decreasing Th/U. Quartz is isotopically equilibrated with magmatic zircon rims. The biotite granite is interpreted to be solely derived by partial melting of old basement rocks of Ganderia and fractionally crystallized at the fO2 of 10−21 to 10−10 bars. The two-mica granite has heterogeneous inherited zircon cores (δ18OZrc of +5.2‰ to 9.9‰) and rims (δ18OZrc of +6.2‰ to 8.7‰), and εHf(t) of −11.7 to −1.01. The two-mica granite was derived from the same basement, but with supracrustal contamination. This open-system process is also recorded by Yb/Gd and Th/U ratios in zircon and isotopic disequilibrium between magmatic zircon rims and quartz (+10.3 ± 0.2‰).