Granulites and garnet–cordierite gneisses from Dronning Maud Land, Antarctica |
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| Authors: | K BUCHER-NURMINEN Y OHTA |
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| Institution: | Mineralogisch-Petrographisches Institut, Albert-Ludwigs Universität, Albertstrasse 23b, D-7800 Freiburg i.Br., Germany;Norwegian Polar Research Institute, Postboks 158, N-1330 Oslo Lufthavn, Norway |
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| Abstract: | Abstract The central sector of Mühlig-Hofmannfjellet (3°E/71°S) in western Dronning Maud Land (East Antarctic shield) is dominated by large intrusive bodies of predominantly orthopyroxene-bearing quartz syenites (charnockites). Metasedimentary rocks are rare; however, two distinct areas with banded gneiss–marble–quartzite sequences of sedimentary origin were found during the Norwegian Antarctic Research Expedition NARE 1989/90. Cordierite-bearing metapelitic gneisses from two different localities contain the characteristic mineral assemblage: cordierite + garnet + biotite + K-feldspar + plagioclase + quartz ± sillimanite ± spinel. Thermobarometry indicates equilibration conditions of about 650°C and 4 kbar. Associated orthopyroxene–garnet granulites, on the other hand, revealed pressures of about 8 kbar and temperatures of 750°C. The earlier granulite facies metamorphism is not well preserved in the cordierite gneisses as a result of excess K-feldspar combined with interaction with an H2O-rich fluid phase, probably released by the cooling intrusives. These two features allowed the original high-grade K-feldspar + garnet assemblages to recrystallize as cordierite–biotite–sillimanite gneisses, completely re-equilibrating them. Phase relationships indicate that the younger metamorphic event occurred in the presence of a fluid phase that varied in composition between the lithologies. |
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| Keywords: | Antarctica garnet–cordierite gneiss granulites mid-crust |
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