Mafic garnet-bearing granulites from Sostrene Island, 150 km southwest of Davis Station on the coast of Prydz Bay, East Antarctica, exhibit two-stage symplectic coronas on garnet, formed after peak metamorphic conditions (Ml). An outer corona of Opx (Mg66)+P1 (An,,)+minor Hbl mantles a finer-grained inner corona of Opx (Mp6,) + PI (An9,,) + Spl (MgX). Both symplectites contain minor ilmenite-magnetite intergrowths. The finer-grained symplectite also occurs along a fracture cleavage in the garnet. The outer corona originated during a second metamorphic event (M2) via the reaction Grt+Cpx (f Hbl) + SiO, = Opx + PI (l), whereas the inner corona formed later in response to decompression and minor deformation, resulting in the fracture cleavage in the garnet, according to the reaction (2). The grossular content of the garent (XGro = 0.168) is almost exactly that which is required for the stoichiometric breakdown by reaction (2) (calculated XGrr = 0.167). The mafic rocks are silica undersaturated, and the SiO, for reaction (1) was most probably derived externally from the surrounding felsic gneisses. Preferred P-T estimates for M1 based on garnet core (Prp~lm,,Grs,,Sps,)-matrix Opx-Cpx-Hbl pairs are c. 10 kbar at 980" C. The fine-grained symplectite formed post-peak M2 at c. 7 kbar and 850" C. The enclosing felsic gneisses yield pressure estimates of between 5 and 7 kbar, which compare with conditions of c. 6 kbar and 775" C in the nearby Bolingen Islands. These lower P-T estimates are considered to be representative of the widespread 1100-Ma metamorphic event recognized in outcrops along the Prydz Bay coast. The high-P, high-T estimates derived from the garnet relics provide evidence for an earlier, possibly Archaean, high-grade metamorphic event.

Sensitive High Resolution Ion MicroProbe (SHRIMP) U–Pb zircon dating of pegmatites from Mount Kirkby, northern Prince Charles Mountains, east Antarctica indicates felsic intrusive activity at 991 ± 22 Ma and 910 ± 18 Ma. Pegmatite emplacement occurred during prolonged high-grade early Neoproterozoic tectonism. These ages correlate well with previously published U–Pb zircon ages obtained from felsic intrusive bodies elsewhere within the northern Prince Charles Mountains. Early Palaeozoic activity at Mount Kirkby is restricted to the emplacement of minor planar pegmatites at 517 ± 12 Ma, which provide a maximum age for local development of discrete extensional mylonites. No conclusive evidence of tectonic or metamorphic events at c. 800 Ma and c. 500 Ma, which have been recently postulated for the region, can be identified from the presently available U–Pb zircon data.

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Reaction textures are often used to derive pressure-temperature-time (P-T-t) paths for metamorphic rocks. However, because dry rocks in particular react very little unless P-T changes are accompanied by deformation and/or fluid influx, it is possible that mineral assemblages and reaction textures in polycyclic rocks record segments of P-T paths that are unrelated in time. Such a case is documented, by garnet Sm-Nd chronology, for a mafic granulite with well-developed two-stage garnet breakdown textures from Ssstrene Island, Prydz Bay, Antarctica. The combined geothermobarometric-geochronological evidence shows that the garnet formed during MI at ca. 1000 Ma, ca. 85CL900"C and 10 kbar. The garnet breakdown reactions producing symplectites of (1) orthopyroxene and plagioclase and (2) orthopyroxene, plagioclase and spinel occurred, respectively, during post-MI decompression and during a second granulite facies metamorphic episode (M2), in response to heating and decompression at ca. 500 Ma, ca. 750°C and 6 kbar. The date for the latter event derives from a nearby garnet-sillimanite gneiss and corresponds to garnet ages which provide evidence for a regional granulite episode extending further north-east along Prydz Bay. These data demonstrate that, in the absence of reliable criteria for heating and cooling and without age constraints, reaction textures cannot be assumed to record pressure or temperature changes in a single thermo-tectonic event. Preservation of the ca. 1000 Ma age of garnet in rocks that have been reheated to ca. 7O&75O0C indicates that the closure temperature for Sm and Nd in garnet is at least 100°C higher than suggested for slowly cooled terranes.