Partial melting of metapelites in the Gagnon terrane below the high-pressure belt in the Manicouagan area (Grenville Province): pressure–temperature (P–T) and U–Pb age constraints and implications
Metapelites of the parautochthonous Gagnon terrane at the footwall of the high-pressure (high-P) belt in the Manicouagan area (central Grenville Province) preserve an impressive textural record of partial melting reactions, mainly in polymineralic inclusions within garnet. The dominant textures were developed within the pressure–temperature (P–T) field of the continuous dehydration melting reaction biotite + kyanite (or sillimanite) + plagioclase + quartz = garnet + K-feldspar + melt, with sillimanite instead of kyanite in the southern part of the footwall. Inferred P–T paths have a hair-pin form in the range of 750–850 °C and 1000–1500 MPa for the kyanite-bearing rocks. Monazite crystallization ages are consistently late Grenvillian, either 995 or 985 Ma, and one sample contains monazite of both ages. Two of these samples also contain inherited monazite with ages of 1738 ± 5 and 1719 ± 30 Ma, indicative of an earlier metamorphic event. Tonalite and diorite from the same area yield Archean zircon crystall...