Helium isotope compositions of the mantle-derived xenoliths and megacrysts from the Cenozoic basalts in Hannuoba were measured. The 3He/ 4He ratios of olivine from xenoliths in Hannuoba vary from 0.15×10 -6 to 7.4×10 -6, obviously lower than those of the MORB, and even lower than the atmospheric helium isotope ratios,implying that the continental mantle is strongly replaced in Hannuoba areas. The 3He/ 4He ratios of pyroxenes and garnets megacrysts vary from 5.7×10 -6 to 24.3×10 -6, and are obviously different from those of the mantle xenoliths. It is inferred that the mantle xenoliths and megacrysts are from different parts of the continental mantle. No necessary relationships in orgin exist between the mantle xenoliths, megacrysts and their host basalts. An extremely high 3He/ 4He ratio of garnet megacryst from Hannuoba was found.
Bulletin of Mineralogy Petrology and Geochemistry