Abstract:
The Ross Orogeny refers to the collision event when East and West Antarctica met, resulting in subduction with associated deformation, crustal thickening, metamorphism and igneous activity. In the Dry Valleys area metamorphic basement rocks are intruded by large plutons of granite. However, further south magmatic rocks are highly varied. The occurrence of nepheline syenites and associated
... carbonatites is unusual as these rocks are associated with crust that is being pulled apart and stretched, not near subduction zone as is associated with the Ross Orogeny. The extent of the anomalous plutonic rock types in the Koettlitz-Walcott Glacier area (ridge system southeast of Dismal Ridge) and the Skelton-Glacier and Hoopers Crag area were sampled for detailed geochemical and geochronological analysis and the area was geologically mapped to determine the extent of the anomalous syenitic plutons. The rock type and its distribution was plotted onto an existing topographic base map. The location of outcrops was facilitated by using aerial photographs, an altimeter and a GPS set. Representative samples were collected for laboratory based geochemical and geochronology analysis. Rocks were thin sectioned and examined petrographically to determine their mineralogy and suitability for chemical analysis. Minerals unidentified by petrography were determined by x-ray diffractions or electron microprobe analysis and further analysed by x-ray fluorescence to determine its chemical composition. The rocks identified by these techniques were analysed by radiometric dating (U-Pb). All data was used to provide a history of tectonic, metamorphic and magmatic events during the Ross Orogeny. 
