PRELIMINARY PETROLOGICAL STUDIES OF THE GRANITIC ROCKS IN THE SOR RONDANE MOUNTAINS, EAST ANTARCTICA

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The Sor Rondane Mountains mainly consist of Proterozoic metamorphic rocks and various kinds of Late Proterozoic to Early Paleozoic granitic rocks. The Early Paleozoic granitic rocks can be divided into two types, concordant granites and discordant granites. Chemical analyses of major and trace elements for the Early Paleozoic granitic rocks are presented. The discordant granites are characterized by high Ba, Sr and alkalies. In contrast, the concordant granites are high in Y and Nb and slightly low in CaO, Cr and Sr compared with the discordant granites. Most of the concordant granites are classified as within plate granites and the discordant granites as volcanic arc granites, based on trace elements. Mineral compositions in the granitic rocks are also related to the two granite types. Mg/(Mg+Fe) ratios of ferromagnesian minerals of the concordant granites are very low, while those of the discordant granites have intermediate Mg/(Mg+Fe) ratios. Anorthite contents of plagioclases in the concordant granites are low, while those of the discordant granites have slightly high anorthite content compared with those of the concordant granites. These chemical features and the Sr initial ratios may suggest that these two granite types were formed under different conditions.
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