Conditions and timing of low-pressure – high-temperature metamorphism in the Montresor Belt, Rae Province, Nunavut
P-T-t estimates for the Montresor Belt, obtained using phase equilibria and geospeedometry modelling integrated with in-situ U-Th-Pb monazite geochronology, shed new light on the tectono-metamorphic effects of the Snowbird phase of the Trans-Hudson orogeny. Typical metapelitic assemblages of the lower Montresor group consist of white mica, biotite, plagioclase, quartz, and andalusite, which in some rocks is partly or completely pseudomorphed by white mica. The observed assemblages reflect peak P-T conditions centering at ca. 575 °C and 3 kbar. Rocks with high bulk Fe/Mg contents contain compositionally zoned garnet, permitting the addition of further constraints on the conditions of metamorphism in the Montresor Belt: Core compositions of earliest-grown garnets indicate initial garnet crystallization at ca. 535 °C and 2.3 kbar suggesting a nearly isobaric P-T path of prograde metamorphism with a gradient of ca. 50 °C/kbar. Chemical age-dating of monazite inclusions in garnet yields ages of ca. 1870 ± 9 to...