Abstract
Nepheline syenite bodies intrude the basement, Koettlitz Group, gneisses of the Transantarctic Mountains of south Victoria Land, Antarctica. A calcite-fluorite-biotite-alkali feldspar dyke has mineralogical, trace element, stable isotope, and radiogenic isotope characteristics similar to the host syenite and distinct from the country rock, Koettlitz Group, marble. The dyke is interpreted as the first carbonatite to be described from Antarctica. Zircon in the carbonatite has been dated by U-Pb techniques as 531+ or -5.5 Ma, early Cambrian. This age occurs within the range of metamorphism, deformation and subduction-related granitoid intrusive events associated with the Ross Orogeny. Whether the nepheline syenite and carbonatite igneous activity occurred strictly contemporaneously with plate convergence and granitoid genesis or marks an extensional interlude, awaits the detailed unravelling of tectonic events along this segment of the Neoproterozoic to early Cambrian margin of Antarctica.