Precambrian geological relationships in high-grade gneisses of the Rauer Islands, east Antarctica
Titel:
Precambrian geological relationships in high-grade gneisses of the Rauer Islands, east Antarctica
Auteur:
Harley, S. L.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 34 (1987) nr. 2 pagina's 175-207
Jaar:
1987-06
Inhoud:
Gneisses from the Rauer Group, near Davis Base, east Antarctica, preserve a complex structural-metamorphic and igneous history. Mafic granulites and paragneisses, preserved as relics and rafts within Proterozoic felsic orthogneisses, were affected by two early deformation episodes (D1 and D2) under granulite facies conditions. Partial melting of the mafic rocktypes occurred subsequent to these events and partly synchronous with the intrusion of syntectonic (D3) felsic orthogneisses. D3, a major episode which resulted in close to isoclinal folding of most of the gneisses in the area, progressed under granulite facies conditions of greater than 800°C and 7-8 kbar. Preliminary isotopic data indicate that D3 can be no older than 1400 Ma. A period of near-isothermal decompression to 4 kbar at 700ˆC late in and following D3 resulted in the production of leucocratic melts from metasedimentary gneisses, prior to the intrusion of discordant basic dykes of probable Late Proterozoic age (1200-1000 Ma). Further deformation, under amphibolite facies conditions, caused refolding of all previous structures about open to tight southeast-plunging folds with wavelengths of up to 2 km. This D4 deformation may be correlated with the major tectonothermal event which caused folding of dykes elsewhere in the Rayner Complex, and probably occurred at 1000-960 Ma. This scheme for the geological evolution of the Rauer Group differs from that of the Proterozoic Rayner Complex in Enderby Land and MacRobertson Land in the recognition of a major Late Proterozoic tectonothermal episode, here termed D3, which pre-dates the intrusion of basic dykes, which were later deformed in a less intense event.
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