COUPLED OS-186 AND OS-187 EVIDENCE FOR CORE-MANTLE INTERACTION

Osmium isotopic analyses of picritic lavas from Hawaii show enrichment s in the osmium-186/osmium-188 ratio (Os-186/Os-188) of 0.008 to 0.018 %, relative to a chondritic upper mantle, that are positively correlat ed with enrichments in Os-187/Os-188 Of 5.4 to 9.0%. The most viable m echanism to produce these coupled Os-186 and Os-187 enrichments is by addition of 0.5 to 1 weight percent of outer core metal to a portion o f the D '' layer and subsequent upwelling of the mixture. These data s uggest that some plumes originate at the core-mantle boundary and that Os isotopes may be used to distinguish plumes derived from shallow ve rsus deep mantle sources.