Metamorphic Evolution of Calc-silicate Body Enclosed in Charnockitic Gneiss at West Ongul Island, Lützow-Holm Complex, East Antarctica

Abstract

Abstract This paper provides a report of a study of a series of boudined bodies of mineralogically zoned calc-silicate bodies, some over 1 m thick, enclosed in granulite facies charnockitic gneisses on West Ongul Island, Lützow-Holm Complex, East Antarctica. Zircons extracted from the centre of one of the calc-silicate bodies indicate that they were metamorphosed around 532.3 ± 0.8 Ma and that the cores of these zircons were inherited from igneous rocks intruded 738.5 ± 1.8 Ma and possibly 605.0 ± 1.2 Ma. The meionite content of scapolite indicates that the peak metamorphic temperature reached a minimum of 790 °C. In the outermost rim of the calc-silicate scapolite is partially replaced by clinopyroxene, probably as a result of the influx of Mg bearing fluids from the surrounding charnockite gneiss during uplift and decompression. An influx of hydrous fluid resulted in the almost complete retrogressive alteration of plagioclase to sericite throughout the calc-silicates, with minor growth of amphibole after clinopyroxene and calcite after scapolite only in the innermost zone.