Hf isotopic compositions of the Hawaii Scientific Drilling Project core and the source mineralogy of Hawaiian basalts

A large suite of Mauna Kea basalts from the Hawaii Scientific Drilling Proj ect cure show a progressive enrichment in radiogenic Hf with time (epsilon( Hf) = +11.4 to +13.1) well-correlated with the increasingly radiogenic char acter of Nd. The alkali basalts erupted at the termination of the Mauna Kea stage are isotopically indistinguishable from the underlying and intercala ted tholeiites. The overlying Mauna Loa flows show the return of a less dep leted character (EKE = +10.5 to +11.6). The Hf and Nd isotopic compositions of the two volcanoes are distinct, even though they may marginally overlap . The isotopic succession can be interpreted with the concentrically zoned plume model of Hauri et al. [1994, 1996] and Lassiter et al. [1996]. Compar ing the Lu/Hf and Sm/Nd ratios of the HSDP basalts with those inferred from the isotopic properties of their mantle source and the mineral composition s deduced from literature mineral partitioning data indicates that the basa lts can be derived by extraction of 10-15 percent melt from a garnet-perido tite residue.