Advection-driven, (ultra-)high temperature metamorphism: A case study from the Shawinigan Orogeny in the Frontenac Terrane, Canada

Ultra-high temperature (UHT) metamorphism, reaching over 900°C at pressures of 8–12 kbar, is increasingly recognized in orogenic belts, but its origin in collisional settings remains debated. In the Frontenac Terrane of the southwestern Grenville Province, deposition of sedimentary rocks was followed by early compressive deformation and intrusion of mafic–felsic magmas during the Shawinigan orogeny (1200–1150 Ma). Detrital zircon ages and geochemistry point to a back-arc setting, while emplacement of the Frontenac Suite granitoids at mid-crustal levels provided the heat that drove UHT metamorphism. Mineral assemblages (orthopyroxene–cordierite–garnet–sillimanite, sapphirine–cordierite, and perthitic feldspar) coupled with phase equilibrium modelling and thermobarometry record conditions exceeding 900°C at ~5–7 kbar, consistent with advective heating from syn-collisional intrusions. Later D2 open folding, oriented obliquely to the Grenville trend, likely reflects uplift and lithospheric delamination, followed by renewed D3 Ottawan shortening and magmatism around 1060 Ma. As post-Shawinigan overprinting is minor and the earlier history is preserved, the Frontenac Terrane is a key record of pre-Ottawan Laurentian margin evolution while providing evidence for the role of syn-collisional magmatism in generating UHT metamorphism within compressional orogens.