Metamorphic P-T conditions and variation of REE between two garnet generations from granulites in the Sør-Rondane mountains, East Antarctica

Abstract

In this paper, we describe the metamorphic conditions of Fe-rich granulite and variations in rare earth elements (REE) between peak garnet porphyroblasts and secondary garnet coronae. The Fe-rich granulites were collected from Vesthaugen, Sor-Rondane Mountains, East Antarctica, and consist mainly of cordierite, garnet, spinel, perthite, K-feldspar, plagioclase, and orthopyroxene or sillimanite. Temperatures estimated from perthitc–mesoperthitic feldspar compositions, experimentally calibrated geothermobarometers and the modeling of P-T pseudosections suggest that the rocks experienced peak ultrahigh-temperature (UHT) metamorphic conditions of 900–950 °C and 5.0 ± 0.5 kbar. Spinel contains quartz inclusions that also provide evidence for UHT metamorphism. Evidence of partial melting is characterized by the presence of leucocratic bands. The second generation of garnet occurs as coronae around spinel, formed during isobaric cooling following the peak conditions of UHT metamorphism. Garnet coronae and garnet porphyroblasts have distinct trace element patterns. Textural evidence and REE geochemistry suggest that the development of garnet coronae was controlled by (1) the REE composition of reactant phases and melt and/or (2) the crystallization of HREE-rich accessory phases (e.g., zircon and monazite) during secondary garnet growth.