Coupled 186Os and 187Os evidence for core-mantle interaction
Osmium isotopic analyses of picritic lavas from Hawaii show enrichments in the osmium-186/osmium-188 ratio (186Os/188Os) of 0. 008 to 0.018%, relative to a chondritic upper mantle, that are positively correlated with enrichments in 187Os/188Os of 5.4 to 9.0%. The most viable mechanism to produce these coupled 186Os and 187Os enrichments is by addition of 0.5 to 1 weight percent of outer core metal to a portion of the D" layer and subsequent upwelling of the mixture. These data suggest that some plumes originate at the core-mantle boundary and that Os isotopes may be used to distinguish plumes derived from shallow versus deep mantle sources.
Brandon
AD
A. D. Brandon, R. J. Walker, J. W. Morgan, Isotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, USA. J. W. Morgan, Department of Earth Resources, Colorado State University, Fort Collins, CO 80.
Walker
RJ
Morgan
JW
Norman
MD
Prichard
HM