The Mesozoic dykes related to the distribution of Karoo plume on the territory of East Antarctica are studied. It is shown that magnesian high-Ti ferrobasalts are found in the area of Ahlmannryggen massif. Their formation is determined by melting of the mantle that contains pyroxenite. The isotope characteristics of the studied dolerites reflect the composition of a pyroxenite source, i.e., the ancient oceanic lithosphere (EMI) that subsided to the mantle depths of 150-170 km in the paleosubduction zone of the continent of Gondwana and was transformed to the pyroxenite melt 180 Ma ago during the interaction with mantle peridotite of the plume.