| Summary: | 122 leaves :ill. 30 cm. Includes bibliography. University of Otago department: Geology. In the Pipecleaner Glacier region, Southern Victoria Land metasediments of the Koettlitz Group have been intruded by nepheline syenites and granitoid plutons, of probable early Paleozoic age. The Radian Ridge nepheline syenite is the smaller (=0.12km²) of two nepheline syenites found within the Pipecleaner - Mt Dromedary area. The mineral assemblage is dominated by Na & K-feldspar, and iron-rich biotite, with muscovite and cancrinite replacing nepheline. Fluorite and calcite are abundant minor phases. Cross cutting the foliation of the nepheline syenite is a 70cm wide carbonatite dyke. Stable isotope values for the dyke are 15.07 δ¹⁸O‰ and -2.24 δ¹³C‰. Calcite from the nepheline syenite has similar values, of 16.8 δ¹⁸O‰ and -2.1 δ¹³C‰. U/Pb dates from 2 zircons extracted from the carbonatite dyke give a minimum age of 531 ± 5.5 Ma for the intrusion of the nepheline syenite. The intrusion of the nepheline syenite probably occurred prior to the subduction-related Paleozoic Ross Orogeny. The Pipecleaner orthogneiss, intercalated with the Salmon marble, Koettlitz group, is a biotite orthogneiss that forms part of the Granite Harbour Intrusives. Major and trace element trends indicate that the calc-alkaline orthogneiss is a composite body with l-type characteristics and affinities with the DVI suite (after Smillie 1989). Garnet-biotite geothermometry suggests a peak metamorphic temperature of 594 ±61°C at 4.8 kb. The orthogneiss is intruded by aplites, both concordant and discordant to the foliation. Small, non-foliated granitic intrusions, unrelated to the aplites of the orthogneiss, occur within the Pipecleaner Glacier area. Part of the Granite Harbour Intrusives, these small (<200m diameter) intrusions occur as plutons and dykes with a NW-SE trend. They are garnet-bearing l-type granites with affinities to the DVI suite.
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