Granulite-facies regional and contact metamorphism of the Tasiuyak paragneiss, northern Labrador: textural evolution and interpretation
The Tasiuyak paragneiss at the western margin of the Nain Plutonic Suite has been subjected to two granulite-facies metamorphic events: (i) regional metamorphism during the Paleoproterozoic Torngat orogeny, and (ii) contact metamorphism due to emplacement of the Mesoproterozoic Nain Plutonic Suite. Regional metamorphism led to partial melting of pelitic rocks and the development of a locally well-preserved sequence of prograde and retrograde textures. These textures are partly controlled by bulk composition and formed in the pressure–temperature (P–T) field of the continuous reaction: biotite + sillimanite + plagioclase + quartz  = garnet + K-feldspar + melt, along a hairpin P–T path with peak conditions of ~8–10 kbar (0.8–1.0 GPa) and up to 870 °C in the NaKFMASH (Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O) system. These textures controlled the development of the contact metamorphic assemblages. Contact metamorphism of the pelitic rocks between the Tessiarsuyungoakh intrusion and the Makhavinekh Lake pluton led to ...