This project will study two suites of xenolith samples of the earth's unexposed crust and mantle brought to the surface in the western Ross Sea, Antarctica, as inclusions in mafic magma, but separated by a time interval of nearly 500 million years. These samples offer the opportunity to better understand the geologic and tectonic history of the enigmatic Transantarctic Mountains region, during both its current uplift phase and its much earlier history as an orogenic belt. Constraints regarding the tectonic history and reconstruction of Gondwanaland should also result as well as increasing our fundamental knowledge and understanding of upper mantle and lower crustal composition and evolution. The results of this study will provide critical information for completion of cross-sections in the Global Transect Program and for interpretations of geophysical data collected internationally in the Ross Sea.