Correlated helium and lead isotope variations in Hawaiian lavas

Abstract

Variations in ^3He/^4He ratios among Hawaiian shield-building and pre-shield basalts are correlated with variations in ^(208)Pb/^(204)Pb and ^(206)Pb/^(204)Pb ratios. Using this correlation, the ^3He/^4He ratio of Hawaiian lavas can be predicted to within 2.9 R_A (mean deviation) between 7 and 32 R_A based only upon the lead isotope composition. This level of prediction is as good as can be expected based upon the precision of lead isotope ratio measurements. This correlation demonstrates a coupling of volatile and nonvolatile elements in the sources of Hawaiian basalts and allows the nonvolatile-element characteristics of the high-^3He/^4He component of the mantle sources of Hawaiian lavas to be defined. This result confirms and extends previous inferences based upon correlations between helium and strontium isotope ratios in individual suites of Hawaiian lavas. The source of high ^3He/^4He ratios in Hawaiian lavas has a higher time-integrated Th/U ratio than the sources of Pacific mid-ocean ridge basalts, consistent with it being a mixture containing primitive mantle or having differentiated in two or more stages from primitive mantle.

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