Pressure–temperature–time path of a metapelite from Mefjell, Sør Rondane Mountains, East Antarctica

Abstract

A metapelite preserving prograde and retrograde zoning in garnet from Mefjell, southern Sør Rondane Mountains (SRM), East Antarctica is described in detail and U–Th–Pb geochronological data are presented. Garnet, sillimanite, staurolite and biotite are in textural equilibrium in the matrix. The garnet shows three distinct compositional zones comprising core, mantle and rim. From core to the mantle, the spessartine content represents a bell–shaped profile. From mantle to the rim, spessartine content increases and pyrope decreases. Kyanite is present as tiny inclusions in the garnet core. The core also contains aggregates of sillimanite with radial cracks around them, interpreted to have resulted from the inversion of kyanite. The prograde P–T path recorded in the garnet is heating to approximately 700 °C at 5.6 kbar with a slight increase in pressure. U–Th–Pb dating of monazite grains yields a large range of age distribution between 700 and 540 Ma. The inferred prograde metamorphism of the metapelite sample in this study might be related to subduction and/or tectonic loading explained by a collision tectonic model of the SRM (Osanai et al., 2013).