Archaean and Proterozoic geological relationships in the Vestfold Hills-Prydz Bay area, Antarctica

The Archaean cratonic block of the Vestfold Hills, Princess Elizabeth Land is one of only three well-documented examples in East Antarctica. It is characterised by tectonically interlayered tonalitic to granitiC orthogneisses (Mossel gneiss) and garnetiferous paragneisses (Chelnok supracrustal assemblage) as well as sub- ordinate units of predominantly mafic granulite (Tryne meta-volcanics). This sequence is cut by a second suite of orthogneisses (Crooked Lake gneiSS), ranging in composition from gabbro-diorite to tonalite and granite, which was emplaced synchronously with the last major phase of deformation. Cutting the gneisses are several suites of Proterozoic tholeiitic dykes, including a high-Mg suite, which range in age from about 2350 Ma to 1300 Ma. Most dykes are unmetamorphosed, but, in the southwestern part of the VestfoldHills, high-pressure garnet-bearing assemblages developed during a late Proterozoic (about 1100 Ma) thermal event. Granulite facies gneisses that crop out southwest of the Vestfold Block, along the coast of Prydz Bay, show the regional effect of this younger metamorphism and form part of an extensive late Proterozoic high-grade terrain, which makes up much of the East Antarctic Shield. Gneisses in the Rauer Group of Islands, within 30 km of the Vestfold Hills, are lithologically similar (predominantly orthogneisses) to those of the Vestfold Block, and contain metamorphosed relics of Vestfold dykes; however, they include only a minor component derived by remetamorphism of Archaean continental crustal rocks. In contrast, gneisses further to the southwest were mainly derived from aluminous sedimentary protoliths, and are quite different in composition to those of the Vestfold Block and Rauer Group. They do not appear to have been intruded by mafic dykes (mafic granulite is very rare) and apparently represent a Proterozoic cover sequence of similar age to metasedimentary sequences in MacRobertson Land. Intrusion of locally fayalite- bearing granitic rocks took place about 500 Ma ago.