Coupled ¹⁸⁶ Os and ¹⁸⁷ Os Evidence for Core-Mantle Interaction

Abstract

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.

A chilled margin of komatiite and Mg-rich basaltic andesite in the western Bushveld Complex, South Africa

“…Fourthly, prior to crustal contamination the B1 suite could have formed from an unusually PGE-rich komatiitic parent liquid, derived from a mantle plume that contained material enriched in late veneer or derived from the Earth's outer core (Brandon et al 1998Humayun 2011). This model provides the best fit with the observed data and is currently favored by us.…”

Evaluation of a technique for determining Re and PGEs in geological samples by ICP-MS coupled with a modified Carius tube digestion

“…Platinum group elements (PGEs) and Re are important for the understanding of petrogenetic processes and evolution of the Earth, e.g., core segregation, coremantle, and mantle-crust interactions (Brandon et al, 1998;Shirey and Walker, 1998). The determination of PGEs in geological materials is difficult because of their low abundance and heterogeneous distributions and the complexity of sample preparation.…”

Platinum group elements in the Emeishan large igneous province, SW China: Implications for mantle sources

“…As the Emeishan picrites are relatively low-degree partial melts , the high Os concentrations in the ELIP picrites cannot be explained by the mechanism proposed by Schaefer et al (2000). An alternative interpretation invokes a small contribution in the mantle source of Os derived from the outer core (e.g., Snow and Schmidt, 1998;Snow et al, 2000), and indeed would be required if core-derived materials were detectable in the lavas through their 186 Os-187 Os characteristics (e.g., Brandon et al, 1998). In addition, high Os concentration also may result from fractional crystallization.…”

“…This is because, as highly siderophilic and mostly compatible elements, PGEs provide complementary information about the Earth's accretion, core-mantle differentition, mantle evolution and magma genesis to that which can be derived from lithophilic incompatible elements (e.g., Brandon et al, 1998Brandon et al, , 1999Puchtel and Humayun, 2000;Rehkämper et al, 1997;Righter et al, 2000). The behavior of PGE during partial melting and crystal fractionation can be studied from PGE compositions of mantle-derived lavas such as basalts and picrites.…”