A Pan‐African granulite facies metamorphic episode in Prydz Bay, Antarctica: Evidence from Sm‐Nd garnet dating

Abstract

The granulite facies gneisses along the Prydz Bay coastline, Antarctica, have long been regarded as part of an extensive Proterozoic (ca 1000 Ma) terrane, based on correlations with other parts of eastern Antarctica. New Sm‐Nd garnet‐whole rock dates for various rocks indicate that the main metamorphic episode that has affected the rocks in Prydz Bay is of Pan‐African age (515–490 Ma). Only in one locality, in the western part of the area, have older garnet ages been found. On Søstrene Island, where petrographic and analytical work suggests an earlier higher pressure metamorphic event, an age of 990 Ma correlates with some well‐established metamorphic ages from the Northern Prince Charles Mountains to the south, the Rayner Complex, Enderby Land to the southwest and part of the Rauer Group to the east. Evidence for reworking of the rocks on Søstrene is provided by the textures and by the 500 Ma ages which have been determined for interlayered pelitic and felsic gneisses. The notion of a continuous Late Proterozoic (ca 1000 Ma) terrane ranging from the Rayner Complex, Enderby Land, in the west to the Northern Prince Charles Mountains and the Rauer Group has to be abandoned. The predominantly pelitic gneisses of the Prydz Bay coast are post‐1000 Ma crust derived from Early Proterozoic sources (as indicated by Nd model age) and metamorphosed at 515–490 Ma. Portions of reworked Late Proterozoic (ca 1000 Ma) basement appear to be rare in this area and have so far only been positively identified on Søstrene Island and, by earlier workers, in the Rauer Group. The Pan‐African thermo‐tectonic event probably occurred as a result of the collision of an Archaean block, represented by part of the Rauer Group, with a composite terrane, consisting of basement, metamorphosed at 1000 Ma, and an overlying cover of predominantly pelitic rocks, represented by the Prydz Bay terrane.